Merge pull request #361 from actions/release/0.3.54

Release version 0.3.54

.github/CODEOWNERS

@@ -1 +1,4 @@
 * @actions/actions-vscode-reviewers
+
+# Owners maintaining https://github.com/actions/runner-images
+/languageservice/src/value-providers/default.ts @actions/runner-images-writers @actions/actions-vscode-reviewers

.github/workflows/buildtest.yml

@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [18.x, 20.x, 22.x]
+        node-version: [20.x, 22.x, 24.x]
 
     steps:
     - uses: actions/checkout@v4
@@ -37,10 +37,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Use Node.js 22.x
+    - name: Use Node.js 24.x
       uses: actions/setup-node@v4
       with:
-        node-version: 22.x
+        node-version: 24.x
         cache: 'npm'
         registry-url: 'https://npm.pkg.github.com'
     - run: npm ci

.github/workflows/publish.yml

@@ -29,7 +29,7 @@ jobs:
 
       - uses: actions/setup-node@v4
         with:
-          node-version: "16"
+          node-version: 24.x
 
       - name: Bump version and push
         run: |

.github/workflows/release.yml

@@ -59,7 +59,7 @@ jobs:
 
     permissions:
       contents: write
-      packages: write
+      id-token: write
 
     env:
       PKG_VERSION: "" # will be set in the workflow
@@ -69,9 +69,8 @@ jobs:
 
       - uses: actions/setup-node@v4
         with:
-          node-version: 22.x
+          node-version: 24.x
           cache: "npm"
-          scope: '@actions'
 
       - name: Parse version from lerna.json
         run: |
@@ -97,13 +96,6 @@ jobs:
             core.summary.addLink(`Release v${{ env.PKG_VERSION }}`, release.data.html_url);
             await core.summary.write();
 
-      - name: setup authentication
-        run: echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" >> .npmrc
-        env:
-          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
-
       - name: Publish packages
         run: |
-          lerna publish ${{ env.PKG_VERSION }} --yes --no-git-reset --no-git-tag-version
+          npx lerna publish ${{ env.PKG_VERSION }} --yes --no-git-reset --no-git-tag-version
-        env:
-          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}

.gitignore

@@ -4,6 +4,9 @@ lerna-debug.log
 node_modules
 .DS_Store
 
+# Nx cache (generated by Lerna/Nx)
+.nx/
+
 # Minified JSON (generated at build time)
 *.min.json
 

.prettierignore

@@ -4,3 +4,4 @@ dist
 *.js
 *.json
 *.d.ts
+/.nx/workspace-data

AGENTS.md

@@ -0,0 +1,33 @@
+# Agents
+
+## Build
+
+```
+npx lerna run build
+```
+
+## Test
+
+```
+npm -w @actions/expressions test
+npm -w @actions/workflow-parser test
+npm -w @actions/languageservice test
+```
+
+## Format
+
+Always run formatting before committing:
+
+```
+npx prettier --write <changed files>
+```
+
+Verify with:
+
+```
+npm run format-check -ws
+```
+
+## Feature flags
+
+Feature flags are defined in `expressions/src/features.ts` (`ExperimentalFeatures` interface + `allFeatureKeys` array). They are plumbed through `ConvertOptions`, `CompletionConfig`, `ValidationConfig`, and `initializationOptions`. When a feature graduates to stable, remove its flag and make the behavior unconditional.

docs/esm-migration-plan.md

@@ -0,0 +1,319 @@
+# ESM Migration Plan: Add File Extensions to Imports
+
+## Overview
+
+This document outlines the plan to migrate from TypeScript's deprecated `"moduleResolution": "node"` (node10) to `"moduleResolution": "node16"` or `"nodenext"`. This change is necessary because the published ESM packages have extensionless imports that don't work correctly in modern ESM environments.
+
+## TL;DR - Remaining Work
+
+- [x] expressions - Migrated ✅
+- [x] workflow-parser - Migrated ✅
+- [x] languageservice - Migrated ✅
+- [x] languageserver - Add `.js` extensions to imports ✅
+- [ ] languageserver - Update `tsconfig.build.json` to `moduleResolution: "node16"` (blocked by vscode-languageserver)
+- [ ] languageserver - Upgrade `vscode-languageserver` to stable v10+ when released
+
+**Blocker:** `vscode-languageserver@8.0.2` lacks ESM exports. Stable v10 with `exports` field needed.
+
+### ⚠️ Important: `skipLibCheck: true` Required
+
+All migrated packages use `skipLibCheck: true` in their `tsconfig.build.json`. This works around a TS2386 "Overload signatures must all be optional or required" error in `@types/node/module.d.ts`.
+
+**Why can't we just fix the error?** The error is in `@types/node`, a third-party package maintained by DefinitelyTyped. We can't modify `node_modules`, and upstream fixes take time.
+
+**Is `skipLibCheck` safe?** Yes. It only skips type checking of `.d.ts` files (declaration files from dependencies). Our own `.ts` source files are still fully type-checked. This is a common and recommended workaround for issues in third-party type definitions.
+
+---
+
+## Issues Fixed
+
+This migration will resolve the following issues:
+
+- **#154** - Upgrade `moduleResolution` from `node` to `node16` or `nodenext` in tsconfig
+- **#110** - Published ESM code has imports without file extensions
+- **#64** - expressions: ERR_MODULE_NOT_FOUND attempting to run example demo script  
+- **#146** - Can not import `@actions/workflow-parser`
+
+## Problem Statement
+
+### Current State
+
+All packages use `"moduleResolution": "node"`:
+
+| Package | moduleResolution | TypeScript |
+|---------|------------------|------------|
+| expressions | `"node"` | ^4.7.4 |
+| workflow-parser | `"node"` | ^4.8.4 |
+| languageservice | `"node"` | ^4.8.4 |
+| languageserver | `"node"` | ^4.8.4 |
+| browser-playground | `"Node16"` ✅ | ^4.9.4 |
+
+This causes TypeScript to emit code like:
+```javascript
+// Published to npm - INVALID ESM
+export { Expr } from "./ast";  // Missing .js extension!
+```
+
+### Why This Fails
+
+ESM in Node.js 12+ **requires** explicit file extensions. When users try to import these packages:
+
+```javascript
+// User's code
+import { Expr } from "@actions/expressions";
+```
+
+Node.js fails with:
+```
+Error [ERR_MODULE_NOT_FOUND]: Cannot find module '.../node_modules/@actions/expressions/dist/ast'
+```
+
+## Migration Strategy
+
+### Option A: TypeScript 5.7+ with `rewriteRelativeImportExtensions` (Recommended)
+
+TypeScript 5.7 introduced a new compiler option that automatically rewrites `.ts` extensions to `.js` in output:
+
+```jsonc
+{
+  "compilerOptions": {
+    "moduleResolution": "node16",  // or "nodenext"
+    "rewriteRelativeImportExtensions": true
+  }
+}
+```
+
+**Source code:**
+```typescript
+import { Expr } from "./ast.ts";
+```
+
+**Compiled output:**
+```javascript
+export { Expr } from "./ast.js";
+```
+
+**Pros:**
+- Source uses `.ts` extensions (matches actual files)
+- Works with Deno (which requires `.ts` extensions)
+- TypeScript automatically transforms to `.js`
+- Modern, forward-looking approach
+
+**Cons:**
+- Requires TypeScript 5.7+
+- Relatively new feature
+- **BUG:** See "Known Issues" section below
+
+### Option B: Manual `.js` Extensions
+
+Use `.js` extensions in source TypeScript files:
+
+```typescript
+import { Expr } from "./ast.js";  // Points to .ts file, but use .js extension
+```
+
+**Pros:**
+- Works with TypeScript 4.7+ (with node16 moduleResolution)
+- Well-established pattern
+- No post-processing needed
+- Works with ts-jest without extra configuration
+
+**Cons:**
+- Confusing - `.js` files don't exist at write time
+- Doesn't work with Deno out of the box
+
+### Recommendation
+
+**Use Option B** (manual `.js` extensions). Option A with `rewriteRelativeImportExtensions` has compatibility issues with ts-jest and requires additional workarounds.
+
+---
+
+## Known Issues and Workarounds (December 2025)
+
+### 1. TypeScript Version Conflicts in Monorepo
+
+**Problem:** The root `node_modules/typescript` was version 4.9.5 (pulled in by `ts-node` and `tsutils` dependencies), while workspace packages specified `^5.8.3`.
+
+**Symptoms:** 
+- `npx tsc --version` showed 4.9.5
+- `require('typescript').version` in ts-jest showed 5.8.3
+- Confusing build failures
+
+**Solution:** Add npm overrides in root `package.json`:
+```json
+{
+  "overrides": {
+    "typescript": "5.8.3"
+  }
+}
+```
+
+### 2. ts-jest Compatibility with TypeScript 5.9+
+
+**Problem:** ts-jest 29.4.6 uses `typescript.JSDocParsingMode.ParseAll` which doesn't exist in TypeScript's ES module exports.
+
+**Error:**
+```
+TypeError: Cannot read properties of undefined (reading 'ParseAll')
+at Object.<anonymous> (node_modules/ts-jest/dist/compiler/ts-compiler.js:43:123)
+```
+
+**Root Cause:** ts-jest accesses `typescript_1.default.JSDocParsingMode.ParseAll` but TypeScript has no default export in ESM.
+
+**Solution:** 
+- Use ts-jest 29.0.3 (older version that doesn't use this API)
+- OR wait for ts-jest fix
+- **Stay on TypeScript 5.8.3, not 5.9+**
+
+### 3. TypeScript `rewriteRelativeImportExtensions` Bug with .d.ts Files
+
+**Problem:** TypeScript's `rewriteRelativeImportExtensions: true` correctly rewrites `.ts` → `.js` in `.js` output files, but **incorrectly keeps `.ts` extensions in `.d.ts` declaration files**.
+
+**Example:**
+- Source: `export { Expr } from "./ast.ts";`
+- Output `index.js`: `export { Expr } from "./ast.js";` ✅ Correct
+- Output `index.d.ts`: `export { Expr } from "./ast.ts";` ❌ Wrong (should be `.js`)
+
+**Upstream Issue:** https://github.com/microsoft/TypeScript/issues/61037 (marked "Help Wanted", in Backlog, NOT FIXED as of Dec 2025)
+
+**Workaround:** Post-process `.d.ts` files with a script. See `script/fix-dts-extensions.cjs`.
+
+**Note:** Since we use Option B (manual `.js` extensions), this bug does not affect our migration.
+
+### 4. yaml Package Internal Types Not Exported
+
+**Problem:** The `yaml` package does not export internal types like `LinePos` and `NodeBase` that are used in `workflow-parser/src/workflows/yaml-object-reader.ts`.
+
+**Error:**
+```
+error TS2305: Module '"yaml"' has no exported member 'LinePos'.
+error TS2305: Module '"yaml"' has no exported member 'NodeBase'.
+```
+
+**Solution:** Define local type aliases in the file that uses them:
+```typescript
+// Local type definitions to replace yaml internal imports
+type LinePos = { line: number; col: number };
+type NodeBase = { range?: [number, number, number] };
+```
+
+### 5. languageserver Blocked by vscode-languageserver Dependency
+
+**Problem:** The `vscode-languageserver` package (v8.0.2) does not have proper ESM exports. When using `moduleResolution: "node16"`, TypeScript requires packages to have an `exports` field in `package.json` for subpath imports to work.
+
+**Error:**
+```
+src/index.ts(6,8): error TS2307: Cannot find module 'vscode-languageserver/browser' or its corresponding type declarations.
+src/connection.ts(1,43): error TS2307: Cannot find module 'vscode-languageserver/node' or its corresponding type declarations.
+```
+
+**Root Cause:** The `vscode-languageserver` package.json only has `main` and `browser` fields, but no `exports` field:
+```json
+{
+  "main": "./lib/node/main.js",
+  "browser": {
+    "./lib/node/main.js": "./lib/browser/main.js"
+  }
+  // No "exports" field!
+}
+```
+
+With `moduleResolution: "node16"`, TypeScript follows Node.js ESM resolution rules which require explicit `exports` for subpath imports like `vscode-languageserver/browser` and `vscode-languageserver/node`.
+
+**Status:** Partial - `.js` extensions added, waiting for stable `vscode-languageserver` release with ESM exports to complete migration.
+
+**Completed:** All relative imports in languageserver source files have been updated to use `.js` extensions. This is compatible with the current `moduleResolution: "node"` and will enable a seamless migration once a stable vscode-languageserver version with ESM exports is available.
+
+**Options to resolve:**
+- Wait for stable vscode-languageserver v10+ with ESM exports
+- Use pre-release `vscode-languageserver@10.0.0-next.16` (has proper exports but is unstable)
+- Fork or patch the dependency
+
+---
+
+## Migration Status
+
+| Package | Tests | ESM Status |
+|---------|-------|------------|
+| expressions | 1068 | ✅ Migrated |
+| workflow-parser | 292 | ✅ Migrated |
+| languageservice | 452 | ✅ Migrated |
+| languageserver | 31 | 🔶 Partial (`.js` extensions added, awaiting stable vscode-languageserver) |
+
+---
+
+## Required Configuration Changes
+
+### tsconfig.build.json (each migrated package)
+
+**Note:** We use **Option B** (manual `.js` extensions in source files) rather than `rewriteRelativeImportExtensions` because Option A caused ts-jest compatibility issues (tests would hang indefinitely).
+
+```json
+{
+  "compilerOptions": {
+    "module": "node16",
+    "moduleResolution": "node16",
+    "skipLibCheck": true,
+    "lib": ["ES2022"],
+    "target": "ES2022"
+  }
+}
+```
+
+The `skipLibCheck: true` is needed to work around @types/node compatibility issues with TypeScript 5.x (TS2386 overload signature errors).
+```
+
+### jest.config.js (each migrated package)
+
+```javascript
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+export default {
+  preset: "ts-jest/presets/default-esm",
+  moduleNameMapper: {
+    "^(\\.{1,2}/.*)\\.js$": "$1",
+    "^(\\.{1,2}/.*)\\.ts$": "$1",
+  },
+  transform: {
+    "^.+\\.tsx?$": [
+      "ts-jest",
+      {
+        useESM: true,
+        isolatedModules: true,
+      },
+    ],
+  },
+  moduleFileExtensions: ["ts", "js"],
+};
+```
+
+### Root package.json
+
+```json
+{
+  "overrides": {
+    "typescript": "5.8.3"
+  }
+}
+```
+
+### Each workspace package.json
+
+```json
+{
+  "devDependencies": {
+    "typescript": "^5.8.3",
+    "ts-jest": "^29.0.3"
+  }
+}
+```
+
+---
+
+## References
+
+- [TypeScript moduleResolution reference](https://www.typescriptlang.org/docs/handbook/modules/reference.html)
+- [TypeScript 5.7 rewriteRelativeImportExtensions](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-7.html#path-rewriting-for-relative-paths)
+- [TypeScript .d.ts extension bug #61037](https://github.com/microsoft/TypeScript/issues/61037)
+- [Node.js ESM mandatory extensions](https://nodejs.org/api/esm.html#mandatory-file-extensions)
+- [ts-jest ESM support](https://kulshekhar.github.io/ts-jest/docs/guides/esm-support)
+- [Community fork that works](https://github.com/boxbuild-io/actions-languageservices/commit/077fb2b58dfd2cca3d6e3df1fdf9e26e75db24ae)

expressions/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@actions/expressions",
-  "version": "0.3.25",
+  "version": "0.3.54",
   "license": "MIT",
   "type": "module",
   "source": "./src/index.ts",
@@ -36,7 +36,7 @@
     "clean": "rimraf dist",
     "format": "prettier --write '**/*.ts'",
     "format-check": "prettier --check '**/*.ts'",
-    "lint": "eslint 'src/**/*.ts'",
+    "lint": "eslint --max-warnings 0 'src/**/*.ts'",
     "lint-fix": "eslint --fix 'src/**/*.ts'",
     "prepublishOnly": "npm run build && npm run test",
     "test": "NODE_OPTIONS=\"--experimental-vm-modules\" jest",
@@ -44,7 +44,7 @@
     "watch": "tsc --build tsconfig.build.json --watch"
   },
   "engines": {
-    "node": ">= 18"
+    "node": ">= 20"
   },
   "files": [
     "dist/**/*"
@@ -60,6 +60,6 @@
     "prettier": "^2.8.3",
     "rimraf": "^3.0.2",
     "ts-jest": "^29.0.3",
-    "typescript": "^4.7.4"
+    "typescript": "^5.8.3"
   }
 }

expressions/src/ast.ts

@@ -1,5 +1,5 @@
-import {ExpressionData} from "./data";
+import {ExpressionData} from "./data/index.js";
-import {Token} from "./lexer";
+import {Token} from "./lexer.js";
 
 export interface ExprVisitor<R> {
   visitLiteral(literal: Literal): R;

expressions/src/completion.test.ts

@@ -1,11 +1,11 @@
-import {complete, CompletionItem, trimTokenVector} from "./completion";
+import {complete, CompletionItem, trimTokenVector} from "./completion.js";
-import {DescriptionDictionary} from "./completion/descriptionDictionary";
+import {DescriptionDictionary} from "./completion/descriptionDictionary.js";
-import {BooleanData} from "./data/boolean";
+import {BooleanData} from "./data/boolean.js";
-import {Dictionary} from "./data/dictionary";
+import {Dictionary} from "./data/dictionary.js";
-import {StringData} from "./data/string";
+import {StringData} from "./data/string.js";
-import {wellKnownFunctions} from "./funcs";
+import {wellKnownFunctions} from "./funcs.js";
-import {FunctionDefinition, FunctionInfo} from "./funcs/info";
+import {FunctionDefinition, FunctionInfo} from "./funcs/info.js";
-import {Lexer, TokenType} from "./lexer";
+import {Lexer, TokenType} from "./lexer.js";
 
 const testContext = new Dictionary(
   {

expressions/src/completion.ts

@@ -1,11 +1,12 @@
-import {DescriptionPair} from "./completion/descriptionDictionary";
+import {DescriptionPair} from "./completion/descriptionDictionary.js";
-import {Dictionary, isDictionary} from "./data/dictionary";
+import {Dictionary, isDictionary} from "./data/dictionary.js";
-import {ExpressionData} from "./data/expressiondata";
+import {ExpressionData} from "./data/expressiondata.js";
-import {Evaluator} from "./evaluator";
+import {Evaluator} from "./evaluator.js";
-import {wellKnownFunctions} from "./funcs";
+import {FeatureFlags} from "./features.js";
-import {FunctionDefinition, FunctionInfo} from "./funcs/info";
+import {wellKnownFunctions} from "./funcs.js";
-import {Lexer, Token, TokenType} from "./lexer";
+import {FunctionDefinition, FunctionInfo} from "./funcs/info.js";
-import {Parser} from "./parser";
+import {Lexer, Token, TokenType} from "./lexer.js";
+import {Parser} from "./parser.js";
 
 export type CompletionItem = {
   label: string;
@@ -26,13 +27,15 @@ export type CompletionItem = {
  * @param context Context available for the expression
  * @param extensionFunctions List of functions available
  * @param functions Optional map of functions to use during evaluation
+ * @param featureFlags Optional feature flags to control which features are enabled
  * @returns Array of completion items
  */
 export function complete(
   input: string,
   context: Dictionary,
   extensionFunctions: FunctionInfo[],
-  functions?: Map<string, FunctionDefinition>
+  functions?: Map<string, FunctionDefinition>,
+  featureFlags?: FeatureFlags
 ): CompletionItem[] {
   // Lex
   const lexer = new Lexer(input);
@@ -63,7 +66,7 @@ export function complete(
     const result = contextKeys(context);
 
     // Merge with functions
-    result.push(...functionItems(extensionFunctions));
+    result.push(...functionItems(extensionFunctions, featureFlags));
 
     return result;
   }
@@ -88,10 +91,15 @@ export function complete(
   return contextKeys(result);
 }
 
-function functionItems(extensionFunctions: FunctionInfo[]): CompletionItem[] {
+function functionItems(extensionFunctions: FunctionInfo[], featureFlags?: FeatureFlags): CompletionItem[] {
   const result: CompletionItem[] = [];
+  const flags = featureFlags ?? new FeatureFlags();
 
   for (const fdef of [...Object.values(wellKnownFunctions), ...extensionFunctions]) {
+    // Filter out case function if feature is disabled
+    if (fdef.name === "case" && !flags.isEnabled("allowCaseFunction")) {
+      continue;
+    }
     result.push({
       label: fdef.name,
       description: fdef.description,

expressions/src/completion/descriptionDictionary.test.ts

@@ -1,5 +1,5 @@
-import {StringData} from "../data";
+import {StringData} from "../data/index.js";
-import {DescriptionDictionary} from "./descriptionDictionary";
+import {DescriptionDictionary} from "./descriptionDictionary.js";
 
 describe("description dictionary", () => {
   it("pairs contains all values", () => {

expressions/src/completion/descriptionDictionary.ts

@@ -1,5 +1,5 @@
-import {Dictionary} from "../data/dictionary";
+import {Dictionary} from "../data/dictionary.js";
-import {ExpressionData, Kind, Pair} from "../data/expressiondata";
+import {ExpressionData, Kind, Pair} from "../data/expressiondata.js";
 
 export type DescriptionPair = Pair & {description?: string};
 

expressions/src/data/array.ts

@@ -1,4 +1,4 @@
-import {ExpressionData, ExpressionDataInterface, Kind, kindStr} from "./expressiondata";
+import {ExpressionData, ExpressionDataInterface, Kind, kindStr} from "./expressiondata.js";
 
 export class Array implements ExpressionDataInterface {
   private v: ExpressionData[] = [];

expressions/src/data/boolean.ts

@@ -1,4 +1,4 @@
-import {ExpressionDataInterface, Kind} from "./expressiondata";
+import {ExpressionDataInterface, Kind} from "./expressiondata.js";
 
 export class BooleanData implements ExpressionDataInterface {
   constructor(public readonly value: boolean) {}

expressions/src/data/dictionary.test.ts

@@ -1,5 +1,5 @@
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
 
 describe("dictionary", () => {
   it("pairs contains all values", () => {

expressions/src/data/dictionary.ts

@@ -1,4 +1,4 @@
-import {ExpressionData, ExpressionDataInterface, Kind, kindStr, Pair} from "./expressiondata";
+import {ExpressionData, ExpressionDataInterface, Kind, kindStr, Pair} from "./expressiondata.js";
 
 export class Dictionary implements ExpressionDataInterface {
   private keys: string[] = [];

expressions/src/data/expressiondata.ts

@@ -1,9 +1,9 @@
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {Null} from "./null";
+import {Null} from "./null.js";
-import {Array} from "./array";
+import {Array} from "./array.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
-import {BooleanData} from "./boolean";
+import {BooleanData} from "./boolean.js";
 
 export enum Kind {
   String = 0,

expressions/src/data/index.ts

@@ -1,9 +1,9 @@
-export {Array} from "./array";
+export {Array} from "./array.js";
-export {BooleanData} from "./boolean";
+export {BooleanData} from "./boolean.js";
-export {Dictionary} from "./dictionary";
+export {Dictionary} from "./dictionary.js";
-export {ExpressionData, Kind} from "./expressiondata";
+export {ExpressionData, Kind} from "./expressiondata.js";
-export {Null} from "./null";
+export {Null} from "./null.js";
-export {NumberData} from "./number";
+export {NumberData} from "./number.js";
-export {replacer} from "./replacer";
+export {replacer} from "./replacer.js";
-export {reviver} from "./reviver";
+export {reviver} from "./reviver.js";
-export {StringData} from "./string";
+export {StringData} from "./string.js";

expressions/src/data/null.ts

@@ -1,4 +1,4 @@
-import {ExpressionDataInterface, Kind} from "./expressiondata";
+import {ExpressionDataInterface, Kind} from "./expressiondata.js";
 
 export class Null implements ExpressionDataInterface {
   public readonly kind = Kind.Null;

expressions/src/data/number.test.ts

@@ -1,4 +1,4 @@
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
 
 describe("number", () => {
   it("coerces to string", () => {

expressions/src/data/number.ts

@@ -1,4 +1,4 @@
-import {ExpressionDataInterface, Kind} from "./expressiondata";
+import {ExpressionDataInterface, Kind} from "./expressiondata.js";
 
 export class NumberData implements ExpressionDataInterface {
   constructor(public readonly value: number) {}

expressions/src/data/replacer.test.ts

@@ -1,9 +1,9 @@
-import {Array} from "./array";
+import {Array} from "./array.js";
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {Null} from "./null";
+import {Null} from "./null.js";
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
-import {replacer} from "./replacer";
+import {replacer} from "./replacer.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
 
 describe("replacer", () => {
   it("null", () => {

expressions/src/data/replacer.ts

@@ -1,9 +1,9 @@
-import {Array} from "./array";
+import {Array} from "./array.js";
-import {BooleanData} from "./boolean";
+import {BooleanData} from "./boolean.js";
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {Null} from "./null";
+import {Null} from "./null.js";
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
 
 /**
  * Replacer can be passed to JSON.stringify to convert an ExpressionData object into plain JSON

expressions/src/data/reviver.test.ts

@@ -1,11 +1,11 @@
-import {Array} from "./array";
+import {Array} from "./array.js";
-import {BooleanData} from "./boolean";
+import {BooleanData} from "./boolean.js";
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {ExpressionData} from "./expressiondata";
+import {ExpressionData} from "./expressiondata.js";
-import {Null} from "./null";
+import {Null} from "./null.js";
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
-import {reviver} from "./reviver";
+import {reviver} from "./reviver.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
 
 describe("reviver", () => {
   const tests: {

expressions/src/data/reviver.ts

@@ -1,10 +1,10 @@
-import {Array as dArray} from "./array";
+import {Array as dArray} from "./array.js";
-import {BooleanData} from "./boolean";
+import {BooleanData} from "./boolean.js";
-import {Dictionary} from "./dictionary";
+import {Dictionary} from "./dictionary.js";
-import {ExpressionData} from "./expressiondata";
+import {ExpressionData} from "./expressiondata.js";
-import {Null} from "./null";
+import {Null} from "./null.js";
-import {NumberData} from "./number";
+import {NumberData} from "./number.js";
-import {StringData} from "./string";
+import {StringData} from "./string.js";
 
 /**
  * Reviver can be passed to `JSON.parse` to convert plain JSON into an `ExpressionData` object.

expressions/src/data/string.ts

@@ -1,4 +1,4 @@
-import {ExpressionDataInterface, Kind} from "./expressiondata";
+import {ExpressionDataInterface, Kind} from "./expressiondata.js";
 
 export class StringData implements ExpressionDataInterface {
   constructor(public readonly value: string) {}

expressions/src/errors.ts

@@ -1,4 +1,4 @@
-import {Pos, Token, tokenString} from "./lexer";
+import {Pos, Token, tokenString} from "./lexer.js";
 
 export const MAX_PARSER_DEPTH = 50;
 export const MAX_EXPRESSION_LENGTH = 21000;
@@ -12,6 +12,7 @@ export enum ErrorType {
   ErrorExceededMaxLength,
   ErrorTooFewParameters,
   ErrorTooManyParameters,
+  ErrorEvenParameters,
   ErrorUnrecognizedContext,
   ErrorUnrecognizedFunction
 }
@@ -42,6 +43,8 @@ function errorDescription(typ: ErrorType): string {
       return "Too few parameters supplied";
     case ErrorType.ErrorTooManyParameters:
       return "Too many parameters supplied";
+    case ErrorType.ErrorEvenParameters:
+      return "Even number of parameters supplied, requires an odd number of parameters";
     case ErrorType.ErrorUnrecognizedContext:
       return "Unrecognized named-value";
     case ErrorType.ErrorUnrecognizedFunction:

expressions/src/evaluator.test.ts

@@ -1,8 +1,8 @@
-import * as data from "./data";
+import * as data from "./data/index.js";
-import {ExpressionEvaluationError} from "./errors";
+import {ExpressionEvaluationError} from "./errors.js";
-import {Evaluator} from "./evaluator";
+import {Evaluator} from "./evaluator.js";
-import {Lexer} from "./lexer";
+import {Lexer} from "./lexer.js";
-import {Parser} from "./parser";
+import {Parser} from "./parser.js";
 
 describe("evaluator", () => {
   const lexAndParse = (input: string) => {

expressions/src/evaluator.ts

@@ -10,14 +10,14 @@ import {
   Logical,
   Star,
   Unary
-} from "./ast";
+} from "./ast.js";
-import * as data from "./data";
+import * as data from "./data/index.js";
-import {FilteredArray} from "./filtered_array";
+import {FilteredArray} from "./filtered_array.js";
-import {wellKnownFunctions} from "./funcs";
+import {wellKnownFunctions} from "./funcs.js";
-import {FunctionDefinition} from "./funcs/info";
+import {FunctionDefinition} from "./funcs/info.js";
-import {idxHelper} from "./idxHelper";
+import {idxHelper} from "./idxHelper.js";
-import {TokenType} from "./lexer";
+import {TokenType} from "./lexer.js";
-import {equals, falsy, greaterThan, lessThan, truthy} from "./result";
+import {equals, falsy, greaterThan, lessThan, truthy} from "./result.js";
 
 export class Evaluator implements ExprVisitor<data.ExpressionData> {
   /**

expressions/src/features.test.ts

@@ -0,0 +1,64 @@
+import {FeatureFlags} from "./features.js";
+
+describe("FeatureFlags", () => {
+  describe("isEnabled", () => {
+    it("returns false by default when no options provided", () => {
+      const flags = new FeatureFlags();
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(false);
+    });
+
+    it("returns false by default when empty options provided", () => {
+      const flags = new FeatureFlags({});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(false);
+    });
+
+    it("returns true when feature is explicitly enabled", () => {
+      const flags = new FeatureFlags({missingInputsQuickfix: true});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(true);
+    });
+
+    it("returns false when feature is explicitly disabled", () => {
+      const flags = new FeatureFlags({missingInputsQuickfix: false});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(false);
+    });
+
+    it("returns true when all is enabled", () => {
+      const flags = new FeatureFlags({all: true});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(true);
+      expect(flags.isEnabled("allowConcurrencyQueue")).toBe(true);
+    });
+
+    it("explicit feature flag takes precedence over all:true", () => {
+      const flags = new FeatureFlags({all: true, missingInputsQuickfix: false});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(false);
+    });
+
+    it("explicit feature flag takes precedence over all:false", () => {
+      const flags = new FeatureFlags({all: false, missingInputsQuickfix: true});
+      expect(flags.isEnabled("missingInputsQuickfix")).toBe(true);
+    });
+  });
+
+  describe("getEnabledFeatures", () => {
+    it("returns empty array when no features enabled", () => {
+      const flags = new FeatureFlags();
+      expect(flags.getEnabledFeatures()).toEqual([]);
+    });
+
+    it("returns enabled features", () => {
+      const flags = new FeatureFlags({missingInputsQuickfix: true});
+      expect(flags.getEnabledFeatures()).toEqual(["missingInputsQuickfix"]);
+    });
+
+    it("returns all features when all is enabled", () => {
+      const flags = new FeatureFlags({all: true});
+      expect(flags.getEnabledFeatures()).toEqual([
+        "missingInputsQuickfix",
+        "blockScalarChompingWarning",
+        "allowCaseFunction",
+        "allowCopilotRequestsPermission",
+        "allowConcurrencyQueue"
+      ]);
+    });
+  });
+});

expressions/src/features.ts

@@ -0,0 +1,97 @@
+/**
+ * Experimental feature flags.
+ *
+ * Individual feature flags take precedence over `all`.
+ * Example: { all: true, missingInputsQuickfix: false } enables all
+ * experimental features EXCEPT missingInputsQuickfix.
+ *
+ * When a feature graduates to stable, its flag becomes a no-op
+ * (the feature will be enabled regardless of the configuration value).
+ */
+export interface ExperimentalFeatures {
+  /**
+   * Enable all experimental features.
+   * Individual feature flags take precedence over this setting.
+   * @default false
+   */
+  all?: boolean;
+
+  /**
+   * Enable quickfix code action for missing required action inputs.
+   * @default false
+   */
+  missingInputsQuickfix?: boolean;
+
+  /**
+   * Warn when block scalars (| or >) use implicit clip chomping,
+   * which adds a trailing newline that may be unintentional.
+   * @default false
+   */
+  blockScalarChompingWarning?: boolean;
+
+  /**
+   * Enable the case() function in expressions.
+   * @default false
+   */
+  allowCaseFunction?: boolean;
+
+  /**
+   * Enable the copilot-requests permission in workflow permissions.
+   * @default false
+   */
+  allowCopilotRequestsPermission?: boolean;
+
+  /**
+   * Enable the queue property in workflow concurrency settings.
+   * @default false
+   */
+  allowConcurrencyQueue?: boolean;
+}
+
+/**
+ * Keys of ExperimentalFeatures that represent actual features (excludes 'all')
+ */
+export type ExperimentalFeatureKey = Exclude<keyof ExperimentalFeatures, "all">;
+
+/**
+ * All known experimental feature keys.
+ * This list must be kept in sync with the ExperimentalFeatures interface.
+ */
+const allFeatureKeys: ExperimentalFeatureKey[] = [
+  "missingInputsQuickfix",
+  "blockScalarChompingWarning",
+  "allowCaseFunction",
+  "allowCopilotRequestsPermission",
+  "allowConcurrencyQueue"
+];
+
+export class FeatureFlags {
+  private readonly features: ExperimentalFeatures;
+
+  constructor(features?: ExperimentalFeatures) {
+    this.features = features ?? {};
+  }
+
+  /**
+   * Check if an experimental feature is enabled.
+   *
+   * Resolution order:
+   * 1. Explicit feature flag (if set)
+   * 2. `all` flag (if set)
+   * 3. false (default)
+   */
+  isEnabled(feature: ExperimentalFeatureKey): boolean {
+    const explicit = this.features[feature];
+    if (explicit !== undefined) {
+      return explicit;
+    }
+    return this.features.all ?? false;
+  }
+
+  /**
+   * Returns list of all enabled experimental features.
+   */
+  getEnabledFeatures(): ExperimentalFeatureKey[] {
+    return allFeatureKeys.filter(key => this.isEnabled(key));
+  }
+}

expressions/src/filtered_array.ts

@@ -1,3 +1,3 @@
-import * as data from "./data";
+import * as data from "./data/index.js";
 
 export class FilteredArray extends data.Array {}

expressions/src/funcs.ts

@@ -1,13 +1,14 @@
-import {ErrorType, ExpressionError} from "./errors";
+import {ErrorType, ExpressionError} from "./errors.js";
-import {contains} from "./funcs/contains";
+import {caseFunc} from "./funcs/case.js";
-import {endswith} from "./funcs/endswith";
+import {contains} from "./funcs/contains.js";
-import {format} from "./funcs/format";
+import {endswith} from "./funcs/endswith.js";
-import {fromjson} from "./funcs/fromjson";
+import {format} from "./funcs/format.js";
-import {FunctionDefinition, FunctionInfo} from "./funcs/info";
+import {fromjson} from "./funcs/fromjson.js";
-import {join} from "./funcs/join";
+import {FunctionDefinition, FunctionInfo} from "./funcs/info.js";
-import {startswith} from "./funcs/startswith";
+import {join} from "./funcs/join.js";
-import {tojson} from "./funcs/tojson";
+import {startswith} from "./funcs/startswith.js";
-import {Token} from "./lexer";
+import {tojson} from "./funcs/tojson.js";
+import {Token} from "./lexer.js";
 
 export type ParseContext = {
   allowUnknownKeywords: boolean;
@@ -16,6 +17,7 @@ export type ParseContext = {
 };
 
 export const wellKnownFunctions: {[name: string]: FunctionDefinition} = {
+  case: caseFunc,
   contains: contains,
   endswith: endswith,
   format: format,
@@ -53,4 +55,9 @@ export function validateFunction(context: ParseContext, identifier: Token, argCo
   if (argCount > f.maxArgs) {
     throw new ExpressionError(ErrorType.ErrorTooManyParameters, identifier);
   }
+
+  // case function requires an odd number of arguments
+  if (name === "case" && argCount % 2 === 0) {
+    throw new ExpressionError(ErrorType.ErrorEvenParameters, identifier);
+  }
 }

expressions/src/funcs/case.ts

@@ -0,0 +1,29 @@
+import {ExpressionData, Kind} from "../data/index.js";
+import {FunctionDefinition} from "./info.js";
+
+export const caseFunc: FunctionDefinition = {
+  name: "case",
+  description:
+    "`case( pred1, val1, pred2, val2, ..., default )`\n\nEvaluates predicates in order and returns the value corresponding to the first predicate that evaluates to `true`. If no predicate matches, it returns the last argument as the default value.",
+  minArgs: 3,
+  maxArgs: Number.MAX_SAFE_INTEGER,
+  call: (...args: ExpressionData[]): ExpressionData => {
+    // Evaluate predicate-result pairs
+    for (let i = 0; i < args.length - 1; i += 2) {
+      const predicate = args[i];
+
+      // Predicate must be a boolean
+      if (predicate.kind !== Kind.Boolean) {
+        throw new Error("case predicate must evaluate to a boolean value");
+      }
+
+      // If predicate is true, return the corresponding result
+      if (predicate.value) {
+        return args[i + 1];
+      }
+    }
+
+    // No predicate matched, return default (last argument)
+    return args[args.length - 1];
+  }
+};

expressions/src/funcs/contains.ts

@@ -1,6 +1,6 @@
-import {BooleanData, ExpressionData, Kind} from "../data";
+import {BooleanData, ExpressionData, Kind} from "../data/index.js";
-import {equals} from "../result";
+import {equals} from "../result.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const contains: FunctionDefinition = {
   name: "contains",

expressions/src/funcs/endswith.ts

@@ -1,6 +1,6 @@
-import {BooleanData, ExpressionData} from "../data";
+import {BooleanData, ExpressionData} from "../data/index.js";
-import {toUpperSpecial} from "../result";
+import {toUpperSpecial} from "../result.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const endswith: FunctionDefinition = {
   name: "endsWith",

expressions/src/funcs/format.test.ts

@@ -1,5 +1,5 @@
-import {Null, NumberData, StringData} from "../data";
+import {Null, NumberData, StringData} from "../data/index.js";
-import {format} from "./format";
+import {format} from "./format.js";
 
 describe("format", () => {
   it("null", () => {

expressions/src/funcs/format.ts

@@ -1,5 +1,5 @@
-import {ExpressionData, StringData} from "../data";
+import {ExpressionData, StringData} from "../data/index.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const format: FunctionDefinition = {
   name: "format",

expressions/src/funcs/fromjson.ts

@@ -1,7 +1,7 @@
-import {ExpressionData} from "../data";
+import {ExpressionData} from "../data/index.js";
-import {reviver} from "../data/reviver";
+import {reviver} from "../data/reviver.js";
-import {ExpressionEvaluationError} from "../errors";
+import {ExpressionEvaluationError} from "../errors.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const fromjson: FunctionDefinition = {
   name: "fromJson",

expressions/src/funcs/info.ts

@@ -1,4 +1,4 @@
-import {ExpressionData} from "../data";
+import {ExpressionData} from "../data/index.js";
 
 export interface FunctionInfo {
   name: string;

expressions/src/funcs/join.ts

@@ -1,5 +1,5 @@
-import {ExpressionData, Kind, StringData} from "../data";
+import {ExpressionData, Kind, StringData} from "../data/index.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const join: FunctionDefinition = {
   name: "join",

expressions/src/funcs/startswith.ts

@@ -1,6 +1,6 @@
-import {BooleanData, ExpressionData} from "../data";
+import {BooleanData, ExpressionData} from "../data/index.js";
-import {toUpperSpecial} from "../result";
+import {toUpperSpecial} from "../result.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const startswith: FunctionDefinition = {
   name: "startsWith",

expressions/src/funcs/tojson.ts

@@ -1,6 +1,6 @@
-import {ExpressionData, StringData} from "../data";
+import {ExpressionData, StringData} from "../data/index.js";
-import {replacer} from "../data/replacer";
+import {replacer} from "../data/replacer.js";
-import {FunctionDefinition} from "./info";
+import {FunctionDefinition} from "./info.js";
 
 export const tojson: FunctionDefinition = {
   name: "toJson",

expressions/src/idxHelper.ts

@@ -1,4 +1,4 @@
-import {ExpressionData} from "./data";
+import {ExpressionData} from "./data/index.js";
 
 export class idxHelper {
   public readonly str: string | undefined;

expressions/src/index.ts

@@ -1,9 +1,10 @@
-export {Expr} from "./ast";
+export {Expr} from "./ast.js";
-export {complete, CompletionItem} from "./completion";
+export {complete, CompletionItem} from "./completion.js";
-export {DescriptionDictionary, DescriptionPair, isDescriptionDictionary} from "./completion/descriptionDictionary";
+export {DescriptionDictionary, DescriptionPair, isDescriptionDictionary} from "./completion/descriptionDictionary.js";
-export * as data from "./data";
+export * as data from "./data/index.js";
-export {ExpressionError, ExpressionEvaluationError} from "./errors";
+export {ExpressionError, ExpressionEvaluationError} from "./errors.js";
-export {Evaluator} from "./evaluator";
+export {Evaluator} from "./evaluator.js";
-export {wellKnownFunctions} from "./funcs";
+export {ExperimentalFeatureKey, ExperimentalFeatures, FeatureFlags} from "./features.js";
-export {Lexer, Result} from "./lexer";
+export {wellKnownFunctions} from "./funcs.js";
-export {Parser} from "./parser";
+export {Lexer, Result} from "./lexer.js";
+export {Parser} from "./parser.js";

expressions/src/lexer.test.ts

@@ -1,4 +1,4 @@
-import {Lexer, Token, TokenType} from "./lexer";
+import {Lexer, Token, TokenType} from "./lexer.js";
 
 describe("lexer", () => {
   const tests: {

expressions/src/lexer.ts

@@ -1,5 +1,5 @@
-import {StringData} from "./data";
+import {StringData} from "./data/index.js";
-import {MAX_EXPRESSION_LENGTH} from "./errors";
+import {MAX_EXPRESSION_LENGTH} from "./errors.js";
 
 export enum TokenType {
   UNKNOWN,

expressions/src/parser.ts

@@ -1,9 +1,20 @@
-import {Binary, ContextAccess, Expr, FunctionCall, Grouping, IndexAccess, Literal, Logical, Star, Unary} from "./ast";
+import {
-import * as data from "./data";
+  Binary,
-import {ErrorType, ExpressionError, MAX_PARSER_DEPTH} from "./errors";
+  ContextAccess,
-import {ParseContext, validateFunction} from "./funcs";
+  Expr,
-import {FunctionInfo} from "./funcs/info";
+  FunctionCall,
-import {Token, TokenType} from "./lexer";
+  Grouping,
+  IndexAccess,
+  Literal,
+  Logical,
+  Star,
+  Unary
+} from "./ast.js";
+import * as data from "./data/index.js";
+import {ErrorType, ExpressionError, MAX_PARSER_DEPTH} from "./errors.js";
+import {ParseContext, validateFunction} from "./funcs.js";
+import {FunctionInfo} from "./funcs/info.js";
+import {Token, TokenType} from "./lexer.js";
 
 export class Parser {
   private extContexts: Map<string, boolean>;

expressions/src/result.test.ts

@@ -1,5 +1,5 @@
-import {BooleanData, ExpressionData, NumberData, StringData} from "./data";
+import {BooleanData, ExpressionData, NumberData, StringData} from "./data/index.js";
-import {coerceTypes, toUpperSpecial} from "./result";
+import {coerceTypes, toUpperSpecial} from "./result.js";
 
 describe("coerceTypes", () => {
   const tests: {

expressions/src/result.ts

@@ -1,4 +1,4 @@
-import * as data from "./data";
+import * as data from "./data/index.js";
 
 export function falsy(d: data.ExpressionData): boolean {
   switch (d.kind) {

expressions/src/xlang.test.ts

@@ -1,14 +1,14 @@
 import * as fs from "fs";
 import * as path from "path";
-import {Expr} from "./ast";
+import {Expr} from "./ast.js";
-import * as data from "./data";
+import * as data from "./data/index.js";
-import {kindStr} from "./data/expressiondata";
+import {kindStr} from "./data/expressiondata.js";
-import {replacer} from "./data/replacer";
+import {replacer} from "./data/replacer.js";
-import {reviver} from "./data/reviver";
+import {reviver} from "./data/reviver.js";
-import {ExpressionError} from "./errors";
+import {ExpressionError} from "./errors.js";
-import {Evaluator} from "./evaluator";
+import {Evaluator} from "./evaluator.js";
-import {Lexer, Result} from "./lexer";
+import {Lexer, Result} from "./lexer.js";
-import {Parser} from "./parser";
+import {Parser} from "./parser.js";
 
 interface TestResult {
   value: data.ExpressionData;

expressions/testdata/case.json

@@ -0,0 +1,157 @@
+{
+  "case": [
+    {
+      "expr": "case(true, 'first', 'default')",
+      "result": { "kind": "String", "value": "first" }
+    },
+    {
+      "expr": "case(false, 'first', 'default')",
+      "result": { "kind": "String", "value": "default" }
+    },
+    {
+      "expr": "case(true, 'first', false, 'second', 'default')",
+      "result": { "kind": "String", "value": "first" }
+    },
+    {
+      "expr": "case(false, 'first', true, 'second', 'default')",
+      "result": { "kind": "String", "value": "second" }
+    },
+    {
+      "expr": "case(false, 'first', false, 'second', 'default')",
+      "result": { "kind": "String", "value": "default" }
+    },
+    {
+      "expr": "case(1 == 1, 'equal', 'not equal')",
+      "result": { "kind": "String", "value": "equal" }
+    },
+    {
+      "expr": "case(1 == 2, 'equal', 'not equal')",
+      "result": { "kind": "String", "value": "not equal" }
+    },
+    {
+      "expr": "case(github.ref == 'refs/heads/main', 'main', github.event_name == 'pull_request', 'pr', 'other')",
+      "contexts": {
+        "github": {
+          "ref": "refs/heads/main",
+          "event_name": "push"
+        }
+      },
+      "result": { "kind": "String", "value": "main" }
+    },
+    {
+      "expr": "case(github.ref == 'refs/heads/main', 'main', github.event_name == 'pull_request', 'pr', 'other')",
+      "contexts": {
+        "github": {
+          "ref": "refs/heads/develop",
+          "event_name": "pull_request"
+        }
+      },
+      "result": { "kind": "String", "value": "pr" }
+    },
+    {
+      "expr": "case(github.ref == 'refs/heads/main', 'main', github.event_name == 'pull_request', 'pr', 'other')",
+      "contexts": {
+        "github": {
+          "ref": "refs/heads/develop",
+          "event_name": "push"
+        }
+      },
+      "result": { "kind": "String", "value": "other" }
+    },
+    {
+      "expr": "case(true, 123, 456)",
+      "result": { "kind": "Number", "value": 123 }
+    },
+    {
+      "expr": "case(false, 123, 456)",
+      "result": { "kind": "Number", "value": 456 }
+    },
+    {
+      "expr": "case(github.event == 'pull_request', 0, 1)",
+      "contexts": {
+        "github": {
+          "event": "pull_request"
+        }
+      },
+      "result": { "kind": "Number", "value": 0 }
+    },
+    {
+      "expr": "case(false, 0, 1)",
+      "result": { "kind": "Number", "value": 1 }
+    },
+    {
+      "expr": "case(true, false, true)",
+      "result": { "kind": "Boolean", "value": false }
+    },
+    {
+      "expr": "case(false, false, true)",
+      "result": { "kind": "Boolean", "value": true }
+    },
+    {
+      "expr": "case(true, '', 'default')",
+      "result": { "kind": "String", "value": "" }
+    },
+    {
+      "expr": "case(false, 'first', '')",
+      "result": { "kind": "String", "value": "" }
+    },
+    {
+      "expr": "case(true, fromJSON('[1,2,3]'), 'default')",
+      "result": { "kind": "Array", "value": [1, 2, 3] }
+    },
+    {
+      "expr": "case(true, fromJSON('{\"key\":\"value\"}'), 'default')",
+      "result": { "kind": "Object", "value": { "key": "value" } }
+    },
+    {
+      "expr": "case(false, 'first', false, 'second', false, 'third', false, 'fourth', 'default')",
+      "result": { "kind": "String", "value": "default" }
+    },
+    {
+      "expr": "case(false, 'first', false, 'second', true, 'third', false, 'fourth', 'default')",
+      "result": { "kind": "String", "value": "third" }
+    },
+    {
+      "expr": "case('not a boolean', 'first', 'default')",
+      "err": {
+        "kind": "evaluation",
+        "value": "case predicate must evaluate to a boolean value"
+      }
+    },
+    {
+      "expr": "case(1, 'first', 'default')",
+      "err": {
+        "kind": "evaluation",
+        "value": "case predicate must evaluate to a boolean value"
+      }
+    },
+    {
+      "expr": "case(null, 'first', 'default')",
+      "err": {
+        "kind": "evaluation",
+        "value": "case predicate must evaluate to a boolean value"
+      }
+    },
+    {
+      "expr": "case(fromJSON('[]'), 'first', 'default')",
+      "err": {
+        "kind": "evaluation",
+        "value": "case predicate must evaluate to a boolean value"
+      }
+    },
+    {
+      "expr": "case(fromJSON('{}'), 'first', 'default')",
+      "err": {
+        "kind": "evaluation",
+        "value": "case predicate must evaluate to a boolean value"
+      }
+    },
+    {
+      "expr": "case(true, 'first', false, 'second')",
+      "err": {
+        "kind": "parsing",
+        "value": "Even number of parameters supplied, requires an odd number of parameters: 'case'. Located at position 1 within expression: case(true, 'first', false, 'second')"
+      }
+    }
+  ]
+}

expressions/tsconfig.build.json

@@ -2,9 +2,12 @@
   "exclude": ["./src/**/*.test.ts"],
   "extends": "./tsconfig.json",
   "compilerOptions": {
+    "module": "node16",
+    "moduleResolution": "node16",
     "declaration": true,
     "declarationMap": true,
     "noEmit": false,
-    "outDir": "./dist"
+    "outDir": "./dist",
+    "skipLibCheck": true
   }
 }

languageserver/README.md

@@ -10,6 +10,14 @@ The [package](https://www.npmjs.com/package/@actions/languageserver) contains Ty
 npm install @actions/languageserver
 ```
 
+To install the language server as a standalone CLI:
+
+```bash
+npm install -g @actions/languageserver
+```
+
+This makes the `actions-languageserver` command available globally.
+
 ## Usage
 
 ### Basic usage using `vscode-languageserver-node`
@@ -76,6 +84,11 @@ export interface InitializationOptions {
    * Desired log level
    */
   logLevel?: LogLevel;
+
+  /**
+   * Experimental features that are opt-in
+   */
+  experimentalFeatures?: ExperimentalFeatures;
 }
 ```
 
@@ -92,6 +105,178 @@ const clientOptions: LanguageClientOptions = {
 const client = new LanguageClient("actions-language", "GitHub Actions Language Server", serverOptions, clientOptions);
 ```
 
+### Experimental Features
+
+The language server supports opt-in experimental features via the `experimentalFeatures` initialization option. These features may change or be removed in between releases.
+
+```typescript
+initializationOptions: {
+  experimentalFeatures: {
+    // Enable all experimental features
+    all: true,
+
+    // Or enable specific features
+    missingInputsQuickfix: true,
+  }
+}
+```
+
+**Available experimental features:**
+
+| Feature | Description |
+|---------|-------------|
+| `missingInputsQuickfix` | Code action to add missing required inputs for actions |
+| `blockScalarChompingWarning` | Warn when block scalars (`\|` or `>`) use implicit clip chomping, which adds a trailing newline that may be unintentional |
+| `allowConcurrencyQueue` | Enable the `concurrency.queue` workflow property |
+
+Individual feature flags take precedence over `all`. For example, `{ all: true, missingInputsQuickfix: false }` enables all experimental features except `missingInputsQuickfix`.
+
+When a feature graduates to stable, its flag becomes a no-op and the feature will be enabled regardless of the configuration value.
+
+### Standalone CLI
+
+After installing globally, you can run the language server directly:
+
+```bash
+actions-languageserver --stdio
+```
+
+This starts the language server using stdio transport, which is the standard way for editors to communicate with language servers.
+
+### In Neovim
+
+#### 1. Install the language server
+
+```bash
+npm install -g @actions/languageserver
+```
+
+#### 2. Set up filetype detection
+
+Add this to your `init.lua` to detect GitHub Actions workflow files:
+
+```lua
+vim.filetype.add({
+  pattern = {
+    [".*/%.github/workflows/.*%.ya?ml"] = "yaml.ghactions",
+  },
+})
+```
+
+This sets the filetype to `yaml.ghactions` for YAML files in `.github/workflows/`, allowing you to keep separate YAML LSP configurations if needed.
+
+#### 3. Create the LSP configuration
+
+As of Neovim 0.11+ you can add this configuration in `~/.config/nvim/lsp/actionsls.lua`:
+
+```lua
+local function get_github_token()
+  local handle = io.popen("gh auth token 2>/dev/null")
+  if not handle then return nil end
+  local token = handle: read("*a"):gsub("%s+", "")
+  handle:close()
+  return token ~= "" and token or nil
+end
+
+local function parse_github_remote(url)
+  if not url or url == "" then return nil end
+
+  -- SSH format: git@github.com:owner/repo.git
+  local owner, repo = url:match("git@github%.com:([^/]+)/([^/%.]+)")
+  if owner and repo then
+    return owner, repo: gsub("%.git$", "")
+  end
+
+  -- HTTPS format: https://github.com/owner/repo.git
+  owner, repo = url:match("github%.com/([^/]+)/([^/%.]+)")
+  if owner and repo then
+    return owner, repo:gsub("%.git$", "")
+  end
+
+  return nil
+end
+
+local function get_repo_info(owner, repo)
+  local cmd = string.format(
+    "gh repo view %s/%s --json id,owner --template '{{.id}}\t{{.owner.type}}' 2>/dev/null",
+    owner,
+    repo
+  )
+  local handle = io.popen(cmd)
+  if not handle then return nil end
+  local result = handle: read("*a"):gsub("%s+$", "")
+  handle:close()
+
+  local id, owner_type = result:match("^(%d+)\t(.+)$")
+  if id then
+    return {
+      id = tonumber(id),
+      organizationOwned = owner_type == "Organization",
+    }
+  end
+  return nil
+end
+
+local function get_repos_config()
+  local handle = io.popen("git rev-parse --show-toplevel 2>/dev/null")
+  if not handle then return nil end
+  local git_root = handle: read("*a"):gsub("%s+", "")
+  handle:close()
+
+  if git_root == "" then return nil end
+
+  handle = io.popen("git remote get-url origin 2>/dev/null")
+  if not handle then return nil end
+  local remote_url = handle:read("*a"):gsub("%s+", "")
+  handle:close()
+
+  local owner, name = parse_github_remote(remote_url)
+  if not owner or not name then return nil end
+
+  local info = get_repo_info(owner, name)
+
+  return {
+    {
+      id = info and info.id or 0,
+      owner = owner,
+      name = name,
+      organizationOwned = info and info.organizationOwned or false,
+      workspaceUri = "file://" .. git_root,
+    },
+  }
+end
+
+return {
+  cmd = { "actions-languageserver", "--stdio" },
+  filetypes = { "yaml.ghactions" },
+  root_markers = { ".git" },
+  init_options = {
+    -- Optional: provide a GitHub token and repo context for added functionality
+    -- (e.g., repository-specific completions)
+    sessionToken = get_github_token(),
+    repos = get_repos_config(),
+  },
+}
+```
+
+#### 4. Enable the LSP
+
+Add to your `init.lua`:
+
+```lua
+vim.lsp.enable('actionsls')
+```
+
+#### 5. Verify it's working
+
+Open any `.github/workflows/*.yml` file and run:
+
+```vim
+:checkhealth vim.lsp
+```
+
+You should see `actionsls` in the list of attached clients.
+
 ## Contributing
 
 See [CONTRIBUTING.md](../CONTRIBUTING.md) at the root of the repository for general guidelines and recommendations.
@@ -110,6 +295,27 @@ or to watch for changes
 npm run watch
 ```
 
+### Running the language server locally
+
+After running
+
+```bash
+npm run build:cli
+npm link
+```
+
+`actions-languageserver` will be available globally. You can start it with:
+
+```bash
+actions-languageserver --stdio
+```
+
+Once linked you can also watch for changes and rebuild automatically:
+
+```bash
+npm run watch:cli
+```
+
 ### Test
 
 ```bash

languageserver/bin/actions-languageserver

@@ -0,0 +1,2 @@
+#!/usr/bin/env node
+import "../dist/cli.bundle.cjs";

languageserver/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@actions/languageserver",
-  "version": "0.3.25",
+  "version": "0.3.54",
   "description": "Language server for GitHub Actions",
   "license": "MIT",
   "type": "module",
@@ -31,20 +31,25 @@
     "url": "https://github.com/actions/languageservices"
   },
   "scripts": {
-    "build": "tsc --build tsconfig.build.json",
+    "build": "tsc --build tsconfig.build.json && npm run build:cli",
+    "build:cli": "esbuild src/index.ts --bundle --platform=node --format=cjs --outfile=dist/cli.bundle.cjs",
     "clean": "rimraf dist",
     "format": "prettier --write '**/*.ts'",
     "format-check": "prettier --check '**/*.ts'",
-    "lint": "eslint 'src/**/*.ts'",
+    "lint": "eslint --max-warnings 0 'src/**/*.ts'",
     "lint-fix": "eslint --fix 'src/**/*.ts'",
     "prepublishOnly": "npm run build && npm run test",
     "test": "NODE_OPTIONS=\"--experimental-vm-modules\" jest",
     "test-watch": "NODE_OPTIONS=\"--experimental-vm-modules\" jest --watch",
-    "watch": "tsc --build tsconfig.build.json --watch"
+    "watch": "tsc --build tsconfig.build.json --watch",
+    "watch:cli": "esbuild src/index.ts --bundle --platform=node --format=cjs --outfile=dist/cli.bundle.cjs --watch"
+  },
+  "bin": {
+    "actions-languageserver": "./bin/actions-languageserver"
   },
   "dependencies": {
-    "@actions/languageservice": "^0.3.25",
+    "@actions/languageservice": "^0.3.54",
-    "@actions/workflow-parser": "^0.3.25",
+    "@actions/workflow-parser": "^0.3.54",
     "@octokit/rest": "^21.1.1",
     "@octokit/types": "^9.0.0",
     "vscode-languageserver": "^8.0.2",
@@ -52,23 +57,26 @@
     "yaml": "^2.1.3"
   },
   "engines": {
-    "node": ">= 18"
+    "node": ">= 20"
   },
   "files": [
-    "dist/**/*"
+    "dist/**/*",
+    "bin/**/*"
   ],
   "devDependencies": {
     "@types/jest": "^29.0.3",
     "@typescript-eslint/eslint-plugin": "^5.56.0",
     "@typescript-eslint/parser": "^5.56.0",
+    "esbuild": "^0.27.1",
     "eslint": "^8.36.0",
     "eslint-config-prettier": "^8.8.0",
     "eslint-plugin-prettier": "^4.2.1",
     "fetch-mock": "^9.11.0",
     "jest": "^29.0.3",
+    "node-fetch": "^2.6.7",
     "prettier": "^2.8.3",
     "rimraf": "^3.0.2",
     "ts-jest": "^29.0.3",
-    "typescript": "^4.8.4"
+    "typescript": "^5.8.3"
   }
 }

languageserver/src/connection.ts

@@ -1,8 +1,18 @@
-import {documentLinks, hover, validate, ValidationConfig} from "@actions/languageservice";
+import {
+  documentLinks,
+  getCodeActions,
+  getInlayHints,
+  hover,
+  validate,
+  ValidationConfig
+} from "@actions/languageservice";
 import {registerLogger, setLogLevel} from "@actions/languageservice/log";
 import {clearCache, clearCacheEntry} from "@actions/languageservice/utils/workflow-cache";
 import {Octokit} from "@octokit/rest";
 import {
+  CodeAction,
+  CodeActionKind,
+  CodeActionParams,
   CompletionItem,
   Connection,
   DocumentLink,
@@ -12,24 +22,27 @@ import {
   HoverParams,
   InitializeParams,
   InitializeResult,
+  InlayHint,
+  InlayHintParams,
   TextDocumentIdentifier,
   TextDocumentPositionParams,
   TextDocuments,
   TextDocumentSyncKind
 } from "vscode-languageserver";
 import {TextDocument} from "vscode-languageserver-textdocument";
-import {getClient} from "./client";
+import {getClient} from "./client.js";
-import {Commands} from "./commands";
+import {Commands} from "./commands.js";
-import {contextProviders} from "./context-providers";
+import {contextProviders} from "./context-providers.js";
-import {descriptionProvider} from "./description-provider";
+import {descriptionProvider} from "./description-provider.js";
-import {getFileProvider} from "./file-provider";
+import {FeatureFlags} from "@actions/expressions";
-import {InitializationOptions, RepositoryContext} from "./initializationOptions";
+import {getFileProvider} from "./file-provider.js";
-import {onCompletion} from "./on-completion";
+import {InitializationOptions, RepositoryContext} from "./initializationOptions.js";
-import {ReadFileRequest, Requests} from "./request";
+import {onCompletion} from "./on-completion.js";
-import {getActionsMetadataProvider} from "./utils/action-metadata";
+import {ReadFileRequest, Requests} from "./request.js";
-import {TTLCache} from "./utils/cache";
+import {getActionsMetadataProvider} from "./utils/action-metadata.js";
-import {timeOperation} from "./utils/timer";
+import {TTLCache} from "./utils/cache.js";
-import {valueProviders} from "./value-providers";
+import {timeOperation} from "./utils/timer.js";
+import {valueProviders} from "./value-providers.js";
 
 export function initConnection(connection: Connection) {
   const documents: TextDocuments<TextDocument> = new TextDocuments(TextDocument);
@@ -39,6 +52,7 @@ export function initConnection(connection: Connection) {
   const cache = new TTLCache();
 
   let hasWorkspaceFolderCapability = false;
+  let featureFlags = new FeatureFlags();
 
   // Register remote console logger with language service
   registerLogger(connection.console);
@@ -62,6 +76,8 @@ export function initConnection(connection: Connection) {
       setLogLevel(options.logLevel);
     }
 
+    featureFlags = new FeatureFlags(options.experimentalFeatures);
+
     const result: InitializeResult = {
       capabilities: {
         textDocumentSync: TextDocumentSyncKind.Full,
@@ -72,6 +88,10 @@ export function initConnection(connection: Connection) {
         hoverProvider: true,
         documentLinkProvider: {
           resolveProvider: false
+        },
+        inlayHintProvider: true,
+        codeActionProvider: {
+          codeActionKinds: [CodeActionKind.QuickFix]
         }
       }
     };
@@ -88,6 +108,11 @@ export function initConnection(connection: Connection) {
   });
 
   connection.onInitialized(() => {
+    const enabledFeatures = featureFlags.getEnabledFeatures();
+    if (enabledFeatures.length > 0) {
+      connection.console.info(`Experimental features enabled: ${enabledFeatures.join(", ")}`);
+    }
+
     if (hasWorkspaceFolderCapability) {
       connection.workspace.onDidChangeWorkspaceFolders(() => {
         clearCache();
@@ -111,7 +136,8 @@ export function initConnection(connection: Connection) {
       actionsMetadataProvider: getActionsMetadataProvider(client, cache),
       fileProvider: getFileProvider(client, cache, repoContext?.workspaceUri, async path => {
         return await connection.sendRequest(Requests.ReadFile, {path} satisfies ReadFileRequest);
-      })
+      }),
+      featureFlags
     };
 
     const result = await validate(textDocument, config);
@@ -128,7 +154,8 @@ export function initConnection(connection: Connection) {
           getDocument(documents, textDocument),
           client,
           repos.find(repo => textDocument.uri.startsWith(repo.workspaceUri)),
-          cache
+          cache,
+          featureFlags
         )
     );
   });
@@ -158,6 +185,23 @@ export function initConnection(connection: Connection) {
     return documentLinks(getDocument(documents, textDocument), repoContext?.workspaceUri);
   });
 
+  connection.languages.inlayHint.on(async ({textDocument}: InlayHintParams): Promise<InlayHint[] | null> => {
+    return timeOperation("inlayHints", () => {
+      return getInlayHints(getDocument(documents, textDocument));
+    });
+  });
+
+  connection.onCodeAction((params: CodeActionParams): CodeAction[] => {
+    const document = getDocument(documents, params.textDocument);
+    return getCodeActions({
+      uri: params.textDocument.uri,
+      documentContent: document.getText(),
+      diagnostics: params.context.diagnostics,
+      only: params.context.only,
+      featureFlags
+    });
+  });
+
   // Make the text document manager listen on the connection
   // for open, change and close text document events
   documents.listen(connection);

languageserver/src/context-providers.test.ts

@@ -1,9 +1,9 @@
 import {data, DescriptionDictionary} from "@actions/expressions";
 import {WorkflowContext} from "@actions/languageservice/context/workflow-context";
 import {Mode} from "@actions/languageservice/context-providers/default";
-import {contextProviders} from "./context-providers";
+import {contextProviders} from "./context-providers.js";
-import {RepositoryContext} from "./initializationOptions";
+import {RepositoryContext} from "./initializationOptions.js";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
 
 describe("contextProviders", () => {
   const mockCache = new TTLCache();

languageserver/src/context-providers.ts

@@ -3,11 +3,11 @@ import {ContextProviderConfig} from "@actions/languageservice";
 import {Mode} from "@actions/languageservice/context-providers/default";
 import {WorkflowContext} from "@actions/languageservice/context/workflow-context";
 import {Octokit} from "@octokit/rest";
-import {getSecrets} from "./context-providers/secrets";
+import {getSecrets} from "./context-providers/secrets.js";
-import {getStepsContext} from "./context-providers/steps";
+import {getStepsContext} from "./context-providers/steps.js";
-import {getVariables} from "./context-providers/variables";
+import {getVariables} from "./context-providers/variables.js";
-import {RepositoryContext} from "./initializationOptions";
+import {RepositoryContext} from "./initializationOptions.js";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
 
 export function contextProviders(
   client: Octokit | undefined,

languageserver/src/context-providers/action-outputs.ts

@@ -1,7 +1,7 @@
 import {ActionOutputs, ActionReference} from "@actions/languageservice/action";
 import {Octokit} from "@octokit/rest";
-import {fetchActionMetadata} from "../utils/action-metadata";
+import {fetchActionMetadata} from "../utils/action-metadata.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
 
 export async function getActionOutputs(
   octokit: Octokit,

languageserver/src/context-providers/secrets.ts

@@ -6,10 +6,10 @@ import {warn} from "@actions/languageservice/log";
 import {isMapping, isString} from "@actions/workflow-parser";
 import {Octokit} from "@octokit/rest";
 
-import {RepositoryContext} from "../initializationOptions";
+import {RepositoryContext} from "../initializationOptions.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {errorStatus} from "../utils/error";
+import {errorStatus} from "../utils/error.js";
-import {getRepoPermission} from "../utils/repo-permission";
+import {getRepoPermission} from "../utils/repo-permission.js";
 
 export async function getSecrets(
   workflowContext: WorkflowContext,

languageserver/src/context-providers/steps.test.ts

@@ -3,9 +3,9 @@ import {getStepsContext as getDefaultStepsContext} from "@actions/languageservic
 import {Octokit} from "@octokit/rest";
 import fetchMock from "fetch-mock";
 
-import {createWorkflowContext} from "../test-utils/workflow-context";
+import {createWorkflowContext} from "../test-utils/workflow-context.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {getStepsContext} from "./steps";
+import {getStepsContext} from "./steps.js";
 
 const workflow = `
 name: Caching Primes
@@ -84,13 +84,17 @@ it("outputs is an incomplete dictionary to allow dynamic outputs", async () => {
 
   // Get the step context
   const stepContext = stepsContext?.get("cache-primes");
-  expect(stepContext).toBeDefined();
+  if (!stepContext) {
-  expect(isDescriptionDictionary(stepContext!)).toBe(true);
+    throw new Error("Expected stepContext to be defined");
+  }
+  expect(isDescriptionDictionary(stepContext)).toBe(true);
 
   // Get the outputs - should be a dictionary, not null
   const outputs = (stepContext as DescriptionDictionary).get("outputs");
-  expect(outputs).toBeDefined();
+  if (!outputs) {
-  expect(isDescriptionDictionary(outputs!)).toBe(true);
+    throw new Error("Expected outputs to be defined");
+  }
+  expect(isDescriptionDictionary(outputs)).toBe(true);
 
   // Outputs should be marked incomplete to allow dynamic outputs
   const outputsDict = outputs as DescriptionDictionary;

languageserver/src/context-providers/steps.ts

@@ -3,8 +3,8 @@ import {parseActionReference} from "@actions/languageservice/action";
 import {WorkflowContext} from "@actions/languageservice/context/workflow-context";
 import {isActionStep} from "@actions/workflow-parser/model/type-guards";
 import {Octokit} from "@octokit/rest";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {getActionOutputs} from "./action-outputs";
+import {getActionOutputs} from "./action-outputs.js";
 
 export async function getStepsContext(
   octokit: Octokit,

languageserver/src/context-providers/variables.ts

@@ -7,10 +7,10 @@ import {isMapping, isString} from "@actions/workflow-parser";
 import {Octokit} from "@octokit/rest";
 import {RequestError} from "@octokit/request-error";
 
-import {RepositoryContext} from "../initializationOptions";
+import {RepositoryContext} from "../initializationOptions.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {errorStatus} from "../utils/error";
+import {errorStatus} from "../utils/error.js";
-import {getRepoPermission} from "../utils/repo-permission";
+import {getRepoPermission} from "../utils/repo-permission.js";
 
 export async function getVariables(
   workflowContext: WorkflowContext,

languageserver/src/description-provider.ts

@@ -1,8 +1,8 @@
 import {DescriptionProvider} from "@actions/languageservice/hover";
 import {Octokit} from "@octokit/rest";
-import {getActionDescription} from "./description-providers/action-description";
+import {getActionDescription} from "./description-providers/action-description.js";
-import {getActionInputDescription} from "./description-providers/action-input";
+import {getActionInputDescription} from "./description-providers/action-input.js";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
 
 export function descriptionProvider(client: Octokit | undefined, cache: TTLCache): DescriptionProvider {
   const getDescription: DescriptionProvider["getDescription"] = async (context, token, path) => {

languageserver/src/description-providers/action-description.test.ts

@@ -1,9 +1,9 @@
 import {Octokit} from "@octokit/rest";
 import fetchMock from "fetch-mock";
-import {createWorkflowContext} from "../test-utils/workflow-context";
+import {createWorkflowContext} from "../test-utils/workflow-context.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {getActionDescription} from "./action-description";
+import {getActionDescription} from "./action-description.js";
-import {actionsCheckoutMetadata} from "../test-utils/action-metadata";
+import {actionsCheckoutMetadata} from "../test-utils/action-metadata.js";
 
 const workflow = `
 name: Hello World

languageserver/src/description-providers/action-description.ts

@@ -2,8 +2,8 @@ import {actionUrl, parseActionReference} from "@actions/languageservice/action";
 import {isActionStep} from "@actions/workflow-parser/model/type-guards";
 import {Step} from "@actions/workflow-parser/model/workflow-template";
 import {Octokit} from "@octokit/rest";
-import {fetchActionMetadata} from "../utils/action-metadata";
+import {fetchActionMetadata} from "../utils/action-metadata.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
 
 export async function getActionDescription(client: Octokit, cache: TTLCache, step: Step): Promise<string | undefined> {
   if (!isActionStep(step)) {

languageserver/src/description-providers/action-input.test.ts

@@ -2,10 +2,10 @@ import {StringToken} from "@actions/workflow-parser/templates/tokens/string-toke
 import {Octokit} from "@octokit/rest";
 import fetchMock from "fetch-mock";
 
-import {actionsCheckoutMetadata} from "../test-utils/action-metadata";
+import {actionsCheckoutMetadata} from "../test-utils/action-metadata.js";
-import {createWorkflowContext} from "../test-utils/workflow-context";
+import {createWorkflowContext} from "../test-utils/workflow-context.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {getActionInputDescription} from "./action-input";
+import {getActionInputDescription} from "./action-input.js";
 
 const workflow = `
 name: Hello World

languageserver/src/description-providers/action-input.ts

@@ -4,8 +4,8 @@ import {isActionStep} from "@actions/workflow-parser/model/type-guards";
 import {Step} from "@actions/workflow-parser/model/workflow-template";
 import {TemplateToken} from "@actions/workflow-parser/templates/tokens/template-token";
 import {Octokit} from "@octokit/rest";
-import {fetchActionMetadata} from "../utils/action-metadata";
+import {fetchActionMetadata} from "../utils/action-metadata.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
 
 export async function getActionInputDescription(
   client: Octokit,

languageserver/src/file-provider.ts

@@ -2,7 +2,7 @@ import {File} from "@actions/workflow-parser/workflows/file";
 import {FileProvider} from "@actions/workflow-parser/workflows/file-provider";
 import {fileIdentifier} from "@actions/workflow-parser/workflows/file-reference";
 import {Octokit} from "@octokit/rest";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
 import * as vscodeURI from "vscode-uri";
 
 export function getFileProvider(

languageserver/src/index.ts

@@ -6,7 +6,7 @@ import {
 } from "vscode-languageserver/browser";
 import {createConnection as createNodeConnection} from "vscode-languageserver/node";
 
-import {initConnection} from "./connection";
+import {initConnection} from "./connection.js";
 
 /** Helper function determining whether we are executing with node runtime */
 function isNode(): boolean {

languageserver/src/initializationOptions.ts

@@ -1,3 +1,4 @@
+import {ExperimentalFeatures} from "@actions/expressions";
 import {LogLevel} from "@actions/languageservice/log";
 export {LogLevel} from "@actions/languageservice/log";
 
@@ -28,6 +29,12 @@ export interface InitializationOptions {
    * If a GitHub Enterprise Server should be used, the URL of the API endpoint, eg "https://ghe.my-company.com/api/v3"
    */
   gitHubApiUrl?: string;
+
+  /**
+   * Experimental features that are opt-in.
+   * Features listed here may change or be removed without notice.
+   */
+  experimentalFeatures?: ExperimentalFeatures;
 }
 
 export interface RepositoryContext {

languageserver/src/on-completion.ts

@@ -1,13 +1,14 @@
 import {complete} from "@actions/languageservice/complete";
+import type {FeatureFlags} from "@actions/expressions";
 import {Octokit} from "@octokit/rest";
 import {CompletionItem, Connection, Position} from "vscode-languageserver";
 import {TextDocument} from "vscode-languageserver-textdocument";
-import {contextProviders} from "./context-providers";
+import {contextProviders} from "./context-providers.js";
-import {getFileProvider} from "./file-provider";
+import {getFileProvider} from "./file-provider.js";
-import {RepositoryContext} from "./initializationOptions";
+import {RepositoryContext} from "./initializationOptions.js";
-import {Requests} from "./request";
+import {Requests} from "./request.js";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
-import {valueProviders} from "./value-providers";
+import {valueProviders} from "./value-providers.js";
 
 export async function onCompletion(
   connection: Connection,
@@ -15,11 +16,13 @@ export async function onCompletion(
   document: TextDocument,
   client: Octokit | undefined,
   repoContext: RepositoryContext | undefined,
-  cache: TTLCache
+  cache: TTLCache,
+  featureFlags?: FeatureFlags
 ): Promise<CompletionItem[]> {
   return await complete(document, position, {
     valueProviderConfig: repoContext && valueProviders(client, repoContext, cache),
     contextProviderConfig: repoContext && contextProviders(client, repoContext, cache),
+    featureFlags,
     fileProvider: getFileProvider(client, cache, repoContext?.workspaceUri, async path => {
       return await connection.sendRequest(Requests.ReadFile, {path});
     })

languageserver/src/utils/action-metadata.test.ts

@@ -1,7 +1,7 @@
 import {Octokit} from "@octokit/rest";
 import fetchMock from "fetch-mock";
-import {fetchActionMetadata} from "./action-metadata";
+import {fetchActionMetadata} from "./action-metadata.js";
-import {TTLCache} from "./cache";
+import {TTLCache} from "./cache.js";
 
 // A simplified version of the action.yml file from actions/checkout
 const actionMetadataContent = `

languageserver/src/utils/action-metadata.ts

@@ -3,8 +3,8 @@ import {ActionsMetadataProvider} from "@actions/languageservice";
 import {error} from "@actions/languageservice/log";
 import {Octokit, RestEndpointMethodTypes} from "@octokit/rest";
 import {parse} from "yaml";
-import {TTLCache} from "./cache";
+import {TTLCache} from "./cache.js";
-import {errorMessage, errorStatus} from "./error";
+import {errorMessage, errorStatus} from "./error.js";
 
 export function getActionsMetadataProvider(
   client: Octokit | undefined,

languageserver/src/utils/repo-permission.ts

@@ -1,9 +1,9 @@
 import {error} from "@actions/languageservice/log";
 import {Octokit} from "@octokit/rest";
-import {RepositoryContext} from "../initializationOptions";
+import {RepositoryContext} from "../initializationOptions.js";
-import {TTLCache} from "./cache";
+import {TTLCache} from "./cache.js";
-import {errorStatus} from "./error";
+import {errorStatus} from "./error.js";
-import {getUsername} from "./username";
+import {getUsername} from "./username.js";
 
 export type RepoPermission = "admin" | "write" | "read" | "none";
 

languageserver/src/utils/username.ts

@@ -1,5 +1,5 @@
 import {Octokit} from "@octokit/rest";
-import {TTLCache} from "./cache";
+import {TTLCache} from "./cache.js";
 
 export async function getUsername(octokit: Octokit, cache: TTLCache): Promise<string> {
   return await cache.get(`/username`, undefined, () => fetchUsername(octokit));

languageserver/src/value-providers.ts

@@ -2,11 +2,11 @@ import {ValueProviderConfig} from "@actions/languageservice";
 import {WorkflowContext} from "@actions/languageservice/context/workflow-context";
 import {ValueProviderKind} from "@actions/languageservice/value-providers/config";
 import {Octokit} from "@octokit/rest";
-import {RepositoryContext} from "./initializationOptions";
+import {RepositoryContext} from "./initializationOptions.js";
-import {TTLCache} from "./utils/cache";
+import {TTLCache} from "./utils/cache.js";
-import {getActionInputValues} from "./value-providers/action-inputs";
+import {getActionInputValues} from "./value-providers/action-inputs.js";
-import {getEnvironments} from "./value-providers/job-environment";
+import {getEnvironments} from "./value-providers/job-environment.js";
-import {getRunnerLabels} from "./value-providers/runs-on";
+import {getRunnerLabels} from "./value-providers/runs-on.js";
 
 export function valueProviders(
   client: Octokit | undefined,

languageserver/src/value-providers/action-inputs.ts

@@ -3,8 +3,8 @@ import {WorkflowContext} from "@actions/languageservice/context/workflow-context
 import {Value} from "@actions/languageservice/value-providers/config";
 import {isActionStep} from "@actions/workflow-parser/model/type-guards";
 import {Octokit} from "@octokit/rest";
-import {fetchActionMetadata} from "../utils/action-metadata";
+import {fetchActionMetadata} from "../utils/action-metadata.js";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
 
 export async function getActionInputs(
   client: Octokit,

languageserver/src/value-providers/job-environment.ts

@@ -1,6 +1,6 @@
 import {Value} from "@actions/languageservice/value-providers/config";
 import {Octokit} from "@octokit/rest";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
 
 export async function getEnvironments(client: Octokit, cache: TTLCache, owner: string, name: string): Promise<Value[]> {
   const environments = await cache.get(`${owner}/${name}/environments`, undefined, () =>

languageserver/src/value-providers/runs-on.ts

@@ -2,8 +2,8 @@ import {log} from "@actions/languageservice/log";
 import {Value} from "@actions/languageservice/value-providers/config";
 import {DEFAULT_RUNNER_LABELS} from "@actions/languageservice/value-providers/default";
 import {Octokit} from "@octokit/rest";
-import {TTLCache} from "../utils/cache";
+import {TTLCache} from "../utils/cache.js";
-import {errorMessage} from "../utils/error";
+import {errorMessage} from "../utils/error.js";
 
 // Limitation: getRunnerLabels returns default hosted labels and labels for repository self-hosted runners.
 // It doesn't return labels for organization runners visible to the repository.

languageserver/tsconfig.build.json

@@ -5,6 +5,7 @@
     "declaration": true,
     "declarationMap": true,
     "noEmit": false,
-    "outDir": "./dist"
+    "outDir": "./dist",
+    "skipLibCheck": true
   }
 }

languageservice/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@actions/languageservice",
-  "version": "0.3.25",
+  "version": "0.3.54",
   "description": "Language service for GitHub Actions",
   "license": "MIT",
   "type": "module",
@@ -35,7 +35,7 @@
     "clean": "rimraf dist",
     "format": "prettier --write '**/*.ts'",
     "format-check": "prettier --check '**/*.ts'",
-    "lint": "eslint 'src/**/*.ts'",
+    "lint": "eslint --max-warnings 0 'src/**/*.ts'",
     "lint-fix": "eslint --fix 'src/**/*.ts'",
     "minify-json": "node ../script/minify-json.js src/context-providers/descriptions.json src/context-providers/events/webhooks.json src/context-providers/events/objects.json src/context-providers/events/schedule.json src/context-providers/events/workflow_call.json",
     "prebuild": "npm run minify-json",
@@ -47,15 +47,15 @@
     "watch": "tsc --build tsconfig.build.json --watch"
   },
   "dependencies": {
-    "@actions/expressions": "^0.3.25",
+    "@actions/expressions": "^0.3.54",
-    "@actions/workflow-parser": "^0.3.25",
+    "@actions/workflow-parser": "^0.3.54",
     "vscode-languageserver-textdocument": "^1.0.7",
     "vscode-languageserver-types": "^3.17.2",
     "vscode-uri": "^3.0.8",
     "yaml": "^2.1.1"
   },
   "engines": {
-    "node": ">= 18"
+    "node": ">= 20"
   },
   "files": [
     "dist/**/*"
@@ -74,6 +74,6 @@
     "rimraf": "^3.0.2",
     "ts-jest": "^29.0.3",
     "ts-node": "^10.9.1",
-    "typescript": "^4.8.4"
+    "typescript": "^5.8.3"
   }
 }

languageservice/src/action.test.ts

@@ -1,4 +1,4 @@
-import {actionIdentifier, parseActionReference as parse} from "./action";
+import {actionIdentifier, parseActionReference as parse} from "./action.js";
 
 describe("parseActionReference", () => {
   it("basic action", () => {

languageservice/src/code-actions/code-actions.ts

@@ -0,0 +1,55 @@
+import {FeatureFlags} from "@actions/expressions";
+import {CodeAction, CodeActionKind, Diagnostic} from "vscode-languageserver-types";
+import {CodeActionContext, CodeActionProvider} from "./types.js";
+import {getQuickfixProviders} from "./quickfix/quickfix-providers.js";
+
+export interface CodeActionParams {
+  uri: string;
+  documentContent: string;
+  diagnostics: Diagnostic[];
+  only?: string[];
+  featureFlags?: FeatureFlags;
+}
+
+export function getCodeActions(params: CodeActionParams): CodeAction[] {
+  const actions: CodeAction[] = [];
+  const context: CodeActionContext = {
+    uri: params.uri,
+    documentContent: params.documentContent,
+    featureFlags: params.featureFlags
+  };
+
+  // Build providers map based on feature flags
+  const providersByKind: Map<string, CodeActionProvider[]> = new Map([
+    [CodeActionKind.QuickFix, getQuickfixProviders(params.featureFlags)]
+    // [CodeActionKind.Refactor, getRefactorProviders(params.featureFlags)],
+    // [CodeActionKind.Source, getSourceProviders(params.featureFlags)],
+    // etc
+  ]);
+
+  // Filter to requested kinds, or use all if none specified
+  const requestedKinds = params.only;
+  const kindsToCheck = requestedKinds
+    ? [...providersByKind.keys()].filter(kind => requestedKinds.some(requested => kind.startsWith(requested)))
+    : [...providersByKind.keys()];
+
+  for (const diagnostic of params.diagnostics) {
+    for (const kind of kindsToCheck) {
+      const providers = providersByKind.get(kind) ?? [];
+      for (const provider of providers) {
+        if (provider.diagnosticCodes.includes(diagnostic.code)) {
+          const action = provider.createCodeAction(context, diagnostic);
+          if (action) {
+            action.kind = kind;
+            action.diagnostics = [diagnostic];
+            actions.push(action);
+          }
+        }
+      }
+    }
+  }
+
+  return actions;
+}
+
+export type {CodeActionContext, CodeActionProvider} from "./types.js";

languageservice/src/code-actions/quickfix/add-missing-inputs.ts

@@ -0,0 +1,245 @@
+import {isMapping} from "@actions/workflow-parser";
+import {MappingToken} from "@actions/workflow-parser/templates/tokens/mapping-token";
+import {ScalarToken} from "@actions/workflow-parser/templates/tokens/scalar-token";
+import {TemplateToken} from "@actions/workflow-parser/templates/tokens/template-token";
+import {CodeAction, Position, TextEdit} from "vscode-languageserver-types";
+import {error} from "../../log.js";
+import {findToken} from "../../utils/find-token.js";
+import {getOrParseWorkflow} from "../../utils/workflow-cache.js";
+import {DiagnosticCode, MissingInputsDiagnosticData} from "../../validate-action-reference.js";
+import {CodeActionContext, CodeActionProvider} from "../types.js";
+
+/**
+ * Information extracted from a step token needed to generate edits
+ */
+interface StepInfo {
+  /** Column where step keys start (1-indexed), e.g., the column of "uses:" */
+  stepKeyColumn: number;
+  /** End line of the step (1-indexed) */
+  stepEndLine: number;
+  /** Detected indent size (spaces per level) */
+  indentSize: number;
+  /** Information about existing with: block, if present */
+  withInfo?: {
+    keyColumn: number;
+    keyEndLine: number;
+    valueEndLine: number;
+    hasChildren: boolean;
+    /** Column of first child input (1-indexed), for indentation detection */
+    firstChildColumn?: number;
+  };
+}
+
+export const addMissingInputsProvider: CodeActionProvider = {
+  diagnosticCodes: [DiagnosticCode.MissingRequiredInputs],
+
+  createCodeAction(context: CodeActionContext, diagnostic): CodeAction | undefined {
+    const data = diagnostic.data as MissingInputsDiagnosticData | undefined;
+    if (!data) {
+      return undefined;
+    }
+
+    // Parse the document to get the step token
+    const stepInfo = getStepInfo(context, diagnostic.range.start);
+    if (!stepInfo) {
+      return undefined;
+    }
+
+    const edits = createInputEdits(data.missingInputs, stepInfo);
+    if (!edits || edits.length === 0) {
+      return undefined;
+    }
+
+    const inputNames = data.missingInputs.map(i => i.name).join(", ");
+
+    return {
+      title: `Add missing input${data.missingInputs.length > 1 ? "s" : ""}: ${inputNames}`,
+      edit: {
+        changes: {
+          [context.uri]: edits
+        }
+      }
+    };
+  }
+};
+
+/**
+ * Parse the document and extract step information needed for generating edits.
+ * Returns undefined if parsing fails or the step token cannot be found.
+ */
+function getStepInfo(context: CodeActionContext, diagnosticPosition: Position): StepInfo | undefined {
+  // Parse the document (uses cache if available from validation)
+  const file = {name: context.uri, content: context.documentContent};
+  const parseResult = getOrParseWorkflow(file, context.uri);
+
+  if (!parseResult.value) {
+    error("Failed to parse workflow for missing inputs quickfix");
+    return undefined;
+  }
+
+  // Find the token at the diagnostic position
+  const {path} = findToken(diagnosticPosition, parseResult.value);
+
+  // Walk up the path to find the step token (regular-step)
+  const stepToken = findStepInPath(path);
+  if (!stepToken) {
+    error("Could not find step token for missing inputs quickfix");
+    return undefined;
+  }
+
+  return extractStepInfo(stepToken);
+}
+
+/**
+ * Find the step token (regular-step) in the token path
+ */
+function findStepInPath(path: TemplateToken[]): MappingToken | undefined {
+  // Walk backwards through path to find the step
+  for (let i = path.length - 1; i >= 0; i--) {
+    if (path[i].definition?.key === "regular-step" && isMapping(path[i])) {
+      return path[i] as MappingToken;
+    }
+  }
+  return undefined;
+}
+
+/**
+ * Extract position and indentation info from a step token
+ */
+function extractStepInfo(stepToken: MappingToken): StepInfo | undefined {
+  if (!stepToken.range) {
+    return undefined;
+  }
+
+  // Get the column of the first key in the step
+  let stepKeyColumn = stepToken.range.start.column;
+  if (stepToken.count > 0) {
+    const firstEntry = stepToken.get(0);
+    if (firstEntry?.key.range) {
+      stepKeyColumn = firstEntry.key.range.start.column;
+    }
+  }
+
+  // Find the with: block if present
+  let withKey: ScalarToken | undefined;
+  let withToken: TemplateToken | undefined;
+  for (const {key, value} of stepToken) {
+    if (key.toString() === "with") {
+      withKey = key;
+      withToken = value;
+      break;
+    }
+  }
+
+  // Calculate indent size
+  let indentSize = 2; // Default
+  let withInfo: StepInfo["withInfo"];
+
+  if (withKey?.range && withToken?.range) {
+    // Has with: block - extract its info
+    const hasChildren = isMapping(withToken) && withToken.count > 0;
+    let firstChildColumn: number | undefined;
+
+    if (hasChildren) {
+      const firstChild = (withToken as MappingToken).get(0);
+      if (firstChild?.key.range) {
+        firstChildColumn = firstChild.key.range.start.column;
+        // Detect indent size from with: children
+        indentSize = firstChildColumn - withKey.range.start.column;
+      }
+    }
+
+    withInfo = {
+      keyColumn: withKey.range.start.column,
+      keyEndLine: withKey.range.end.line,
+      valueEndLine: withToken.range.end.line,
+      hasChildren,
+      firstChildColumn
+    };
+  } else {
+    // No with: block - detect indent size using heuristics
+    // Based on the step key column position, estimate indent size
+    // 2-space indent files typically have step keys at column 7
+    // 4-space indent files typically have step keys at column 15
+    const zeroIndexedCol = stepKeyColumn - 1;
+    if (zeroIndexedCol >= 10) {
+      indentSize = 4;
+    }
+  }
+
+  return {
+    stepKeyColumn,
+    stepEndLine: stepToken.range.end.line,
+    indentSize,
+    withInfo
+  };
+}
+
+/**
+ * Generate text edits to add missing inputs
+ */
+function createInputEdits(missingInputs: MissingInputsDiagnosticData["missingInputs"], stepInfo: StepInfo): TextEdit[] {
+  const formatInputLines = (indent: string) =>
+    missingInputs.map(input => {
+      const value = input.default ?? '""';
+      return `${indent}${input.name}: ${value}`;
+    });
+
+  if (stepInfo.withInfo) {
+    // `with:` exists - add inputs to existing block
+    const withIndent = stepInfo.withInfo.keyColumn - 1; // 0-indexed
+    const inputIndentSize = stepInfo.withInfo.firstChildColumn
+      ? stepInfo.withInfo.firstChildColumn - stepInfo.withInfo.keyColumn
+      : stepInfo.indentSize;
+
+    const inputIndent = " ".repeat(withIndent + inputIndentSize);
+    const inputLines = formatInputLines(inputIndent);
+
+    // Calculate insert position
+    let insertLine: number;
+    if (stepInfo.withInfo.hasChildren) {
+      // Insert after the last child (at end of with: block)
+      // valueEndLine is 1-indexed, we want 0-indexed for Position
+      insertLine = stepInfo.withInfo.valueEndLine - 1;
+    } else {
+      // Empty with: block - insert on the next line after with:
+      // keyEndLine is 1-indexed, convert to 0-indexed and go to next line
+      insertLine = stepInfo.withInfo.keyEndLine;
+    }
+
+    const insertPosition: Position = {
+      line: insertLine,
+      character: 0
+    };
+
+    return [
+      {
+        range: {start: insertPosition, end: insertPosition},
+        newText: inputLines.map(line => line + "\n").join("")
+      }
+    ];
+  } else {
+    // No `with:` key - add `with:` at the same level as other step keys
+    const withKeyIndent = stepInfo.stepKeyColumn - 1; // 0-indexed (columns are 1-based)
+
+    const withIndent = " ".repeat(withKeyIndent);
+    const inputIndent = " ".repeat(withKeyIndent + stepInfo.indentSize);
+    const inputLines = formatInputLines(inputIndent);
+
+    const newText = `${withIndent}with:\n` + inputLines.map(line => `${line}\n`).join("");
+
+    // Insert at end of step
+    // stepEndLine is 1-indexed, we want 0-indexed and insert before the line after
+    const insertPosition: Position = {
+      line: stepInfo.stepEndLine - 1,
+      character: 0
+    };
+
+    return [
+      {
+        range: {start: insertPosition, end: insertPosition},
+        newText
+      }
+    ];
+  }
+}

languageservice/src/code-actions/quickfix/quickfix-providers.ts

@@ -0,0 +1,13 @@
+import {FeatureFlags} from "@actions/expressions";
+import {CodeActionProvider} from "../types.js";
+import {addMissingInputsProvider} from "./add-missing-inputs.js";
+
+export function getQuickfixProviders(featureFlags?: FeatureFlags): CodeActionProvider[] {
+  const providers: CodeActionProvider[] = [];
+
+  if (featureFlags?.isEnabled("missingInputsQuickfix")) {
+    providers.push(addMissingInputsProvider);
+  }
+
+  return providers;
+}

languageservice/src/code-actions/tests/runner.test.ts

@@ -0,0 +1,90 @@
+import * as path from "path";
+import {fileURLToPath} from "url";
+import {loadTestCases, runTestCase} from "./runner.js";
+import {ValidationConfig} from "../../validate.js";
+import {ActionMetadata, ActionReference} from "../../action.js";
+import {clearCache} from "../../utils/workflow-cache.js";
+
+// ESM-compatible __dirname
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+// Mock action metadata provider for tests
+const validationConfig: ValidationConfig = {
+  actionsMetadataProvider: {
+    fetchActionMetadata: (ref: ActionReference): Promise<ActionMetadata | undefined> => {
+      const key = `${ref.owner}/${ref.name}@${ref.ref}`;
+
+      const metadata: Record<string, ActionMetadata> = {
+        "actions/cache@v1": {
+          name: "Cache",
+          description: "Cache dependencies",
+          inputs: {
+            path: {
+              description: "A list of files to cache",
+              required: true
+            },
+            key: {
+              description: "Cache key",
+              required: true
+            },
+            "restore-keys": {
+              description: "Restore keys",
+              required: false
+            }
+          }
+        },
+        "actions/setup-node@v3": {
+          name: "Setup Node",
+          description: "Setup Node.js",
+          inputs: {
+            "node-version": {
+              description: "Node version",
+              required: true,
+              default: "16"
+            }
+          }
+        }
+      };
+
+      return Promise.resolve(metadata[key]);
+    }
+  }
+};
+
+// Point to the source testdata directory
+const testdataDir = path.join(__dirname, "testdata");
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("code action golden tests", () => {
+  const testCases = loadTestCases(testdataDir);
+
+  if (testCases.length === 0) {
+    it.todo("no test cases found - add .yml files to testdata/");
+    return;
+  }
+
+  for (const testCase of testCases) {
+    it(testCase.name, async () => {
+      const result = await runTestCase(testCase, validationConfig);
+
+      if (!result.passed) {
+        let errorMessage = result.error || "Test failed";
+
+        if (result.expected !== undefined && result.actual !== undefined) {
+          errorMessage += "\n\n";
+          errorMessage += "=== EXPECTED (golden file) ===\n";
+          errorMessage += result.expected;
+          errorMessage += "\n\n";
+          errorMessage += "=== ACTUAL ===\n";
+          errorMessage += result.actual;
+        }
+
+        throw new Error(errorMessage);
+      }
+    });
+  }
+});

languageservice/src/code-actions/tests/runner.ts

@@ -0,0 +1,231 @@
+import * as fs from "fs";
+import * as path from "path";
+import {TextEdit} from "vscode-languageserver-types";
+import {TextDocument} from "vscode-languageserver-textdocument";
+import {FeatureFlags} from "@actions/expressions";
+import {validate, ValidationConfig} from "../../validate.js";
+import {getCodeActions, CodeActionParams} from "../code-actions.js";
+
+// Marker pattern: # want "diagnostic message" fix="code-action-name"
+const MARKER_PATTERN = /#\s*want\s+"([^"]+)"(?:\s+fix="([^"]+)")?/;
+
+export interface TestCase {
+  name: string;
+  inputPath: string;
+  goldenPath: string;
+  input: string;
+  golden: string;
+  markers: Marker[];
+}
+
+export interface Marker {
+  line: number;
+  message: string;
+  fix?: string;
+}
+
+export interface TestResult {
+  name: string;
+  passed: boolean;
+  error?: string;
+  expected?: string;
+  actual?: string;
+}
+
+/**
+ * Parse markers from input file content
+ */
+export function parseMarkers(content: string): Marker[] {
+  const lines = content.split("\n");
+  const markers: Marker[] = [];
+
+  for (let i = 0; i < lines.length; i++) {
+    const match = lines[i].match(MARKER_PATTERN);
+    if (match) {
+      markers.push({
+        line: i,
+        message: match[1],
+        fix: match[2]
+      });
+    }
+  }
+
+  return markers;
+}
+
+/**
+ * Strip markers from content (for processing)
+ */
+export function stripMarkers(content: string): string {
+  return content
+    .split("\n")
+    .map(line => line.replace(MARKER_PATTERN, "").trimEnd())
+    .join("\n");
+}
+
+/**
+ * Load all test cases from a testdata directory
+ */
+export function loadTestCases(testdataDir: string): TestCase[] {
+  const testCases: TestCase[] = [];
+
+  function walkDir(dir: string) {
+    const entries = fs.readdirSync(dir, {withFileTypes: true});
+
+    for (const entry of entries) {
+      const fullPath = path.join(dir, entry.name);
+
+      if (entry.isDirectory()) {
+        walkDir(fullPath);
+      } else if (entry.isFile() && entry.name.endsWith(".yml") && !entry.name.endsWith(".golden.yml")) {
+        const goldenPath = fullPath.replace(".yml", ".golden.yml");
+
+        if (fs.existsSync(goldenPath)) {
+          const input = fs.readFileSync(fullPath, "utf-8");
+          const golden = fs.readFileSync(goldenPath, "utf-8");
+
+          testCases.push({
+            name: path.relative(testdataDir, fullPath),
+            inputPath: fullPath,
+            goldenPath,
+            input,
+            golden,
+            markers: parseMarkers(input)
+          });
+        }
+      }
+    }
+  }
+
+  walkDir(testdataDir);
+  return testCases;
+}
+
+/**
+ * Apply text edits to a document
+ */
+export function applyEdits(content: string, edits: TextEdit[]): string {
+  // Sort edits in reverse order by position to apply from bottom to top
+  const sortedEdits = [...edits].sort((a, b) => {
+    if (b.range.start.line !== a.range.start.line) {
+      return b.range.start.line - a.range.start.line;
+    }
+    return b.range.start.character - a.range.start.character;
+  });
+
+  const lines = content.split("\n");
+
+  for (const edit of sortedEdits) {
+    const startLine = edit.range.start.line;
+    const startChar = edit.range.start.character;
+    const endLine = edit.range.end.line;
+    const endChar = edit.range.end.character;
+
+    const before = lines[startLine].slice(0, startChar);
+    const after = lines[endLine].slice(endChar);
+
+    const newLines = edit.newText.split("\n");
+    newLines[0] = before + newLines[0];
+    newLines[newLines.length - 1] = newLines[newLines.length - 1] + after;
+
+    lines.splice(startLine, endLine - startLine + 1, ...newLines);
+  }
+
+  return lines.join("\n");
+}
+
+/**
+ * Run a single test case
+ */
+export async function runTestCase(testCase: TestCase, validationConfig: ValidationConfig): Promise<TestResult> {
+  const strippedInput = stripMarkers(testCase.input);
+  const document = TextDocument.create("file:///test.yml", "yaml", 1, strippedInput);
+
+  // 1. Validate and get diagnostics
+  const diagnostics = await validate(document, validationConfig);
+
+  // 2.  Verify all expected diagnostics are present
+  const missingDiagnostics: string[] = [];
+  for (const marker of testCase.markers) {
+    const found = diagnostics.find(d => d.range.start.line === marker.line && d.message.includes(marker.message));
+    if (!found) {
+      missingDiagnostics.push(`line ${marker.line}: "${marker.message}"`);
+    }
+  }
+
+  if (missingDiagnostics.length > 0) {
+    return {
+      name: testCase.name,
+      passed: false,
+      error: `Missing expected diagnostics:\n  ${missingDiagnostics.join(
+        "\n  "
+      )}\n\nActual diagnostics:\n  ${diagnostics.map(d => `line ${d.range.start.line}: "${d.message}"`).join("\n  ")}`
+    };
+  }
+
+  // 3.  Collect all edits from all matching code actions
+  const allEdits: TextEdit[] = [];
+
+  for (const marker of testCase.markers) {
+    if (!marker.fix) {
+      continue;
+    }
+
+    const diagnostic = diagnostics.find(d => d.range.start.line === marker.line && d.message.includes(marker.message));
+
+    if (!diagnostic) {
+      continue; // Already reported above
+    }
+
+    const params: CodeActionParams = {
+      uri: document.uri,
+      documentContent: strippedInput,
+      diagnostics: [diagnostic],
+      featureFlags: new FeatureFlags({all: true})
+    };
+
+    const actions = getCodeActions(params);
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion -- marker.fix is checked at the start of the loop
+    const matchingAction = actions.find(a => a.title.toLowerCase().includes(marker.fix!.toLowerCase()));
+
+    if (!matchingAction) {
+      return {
+        name: testCase.name,
+        passed: false,
+        error: `Code action "${marker.fix}" not found for diagnostic on line ${marker.line}.\nAvailable actions: ${
+          actions.map(a => a.title).join(", ") || "(none)"
+        }`
+      };
+    }
+
+    if (!matchingAction.edit?.changes) {
+      return {
+        name: testCase.name,
+        passed: false,
+        error: `Code action "${marker.fix}" has no edits`
+      };
+    }
+
+    const edits = matchingAction.edit.changes[document.uri] || [];
+    allEdits.push(...edits);
+  }
+
+  // 4. Apply all edits and compare to golden file
+  const actualOutput = applyEdits(strippedInput, allEdits);
+  const expectedOutput = testCase.golden;
+
+  if (actualOutput.trim() !== expectedOutput.trim()) {
+    return {
+      name: testCase.name,
+      passed: false,
+      error: "Output does not match golden file",
+      expected: expectedOutput,
+      actual: actualOutput
+    };
+  }
+
+  return {
+    name: testCase.name,
+    passed: true
+  };
+}

languageservice/src/code-actions/tests/testdata/quickfix/existing-with-key-without-inputs.golden.yml

@@ -0,0 +1,9 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1
+        with:
+          path: ""
+          key: ""

languageservice/src/code-actions/tests/testdata/quickfix/existing-with-key-without-inputs.yml

@@ -0,0 +1,7 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1
+        with: # want "Missing required inputs: `path`, `key`" fix="Add missing inputs: path, key"

languageservice/src/code-actions/tests/testdata/quickfix/existing-with-key.golden.yml

@@ -0,0 +1,10 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1
+        with:
+          restore-keys: ${{ runner.os }}-
+          path: ""
+          key: ""

languageservice/src/code-actions/tests/testdata/quickfix/existing-with-key.yml

@@ -0,0 +1,8 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1
+        with: # want "Missing required inputs: `path`, `key`" fix="Add missing inputs: path, key"
+          restore-keys: ${{ runner.os }}-

languageservice/src/code-actions/tests/testdata/quickfix/four-space-indent.golden.yml

@@ -0,0 +1,9 @@
+on: push
+jobs:
+    build:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/cache@v1
+              with:
+                  path: ""
+                  key: ""

languageservice/src/code-actions/tests/testdata/quickfix/four-space-indent.yml

@@ -0,0 +1,6 @@
+on: push
+jobs:
+    build:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/cache@v1 # want "Missing required inputs: `path`, `key`" fix="Add missing inputs: path, key"

languageservice/src/code-actions/tests/testdata/quickfix/no-with-key.golden.yml

@@ -0,0 +1,9 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1
+        with:
+          path: ""
+          key: ""

languageservice/src/code-actions/tests/testdata/quickfix/no-with-key.yml

@@ -0,0 +1,6 @@
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/cache@v1 # want "Missing required inputs: `path`, `key`" fix="Add missing inputs: path, key"

languageservice/src/code-actions/types.ts

@@ -0,0 +1,23 @@
+import {FeatureFlags} from "@actions/expressions";
+import {CodeAction, Diagnostic} from "vscode-languageserver-types";
+
+export interface CodeActionContext {
+  uri: string;
+  documentContent: string;
+  featureFlags?: FeatureFlags;
+}
+
+/**
+ * A provider that can produce a code action for a given diagnostic
+ */
+export interface CodeActionProvider {
+  /**
+   * The diagnostic codes this provider handles
+   */
+  diagnosticCodes: (string | number | undefined)[];
+
+  /**
+   * Create a code action for the diagnostic, if applicable
+   */
+  createCodeAction(context: CodeActionContext, diagnostic: Diagnostic): CodeAction | undefined;
+}