Setup CodeActions and add quickfix for missing inputs

languageserver/script/esbuild

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+npx esbuild src/index.ts \
+  --bundle \
+  --platform=node \
+  --target=node18 \
+  --format=cjs \
+  --outfile=dist/server-bundled.cjs \
+  --external:vscode \
+  --loader:.json=json

languageserver/src/connection.ts

@@ -1,8 +1,11 @@
-import {documentLinks, 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 { documentLinks, getCodeActions, 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,
@@ -17,19 +20,19 @@ import {
   TextDocuments,
   TextDocumentSyncKind
 } from "vscode-languageserver";
-import {TextDocument} from "vscode-languageserver-textdocument";
-import {getClient} from "./client";
-import {Commands} from "./commands";
-import {contextProviders} from "./context-providers";
-import {descriptionProvider} from "./description-provider";
-import {getFileProvider} from "./file-provider";
-import {InitializationOptions, RepositoryContext} from "./initializationOptions";
-import {onCompletion} from "./on-completion";
-import {ReadFileRequest, Requests} from "./request";
-import {getActionsMetadataProvider} from "./utils/action-metadata";
-import {TTLCache} from "./utils/cache";
-import {timeOperation} from "./utils/timer";
-import {valueProviders} from "./value-providers";
+import { TextDocument } from "vscode-languageserver-textdocument";
+import { getClient } from "./client";
+import { Commands } from "./commands";
+import { contextProviders } from "./context-providers";
+import { descriptionProvider } from "./description-provider";
+import { getFileProvider } from "./file-provider";
+import { InitializationOptions, RepositoryContext } from "./initializationOptions";
+import { onCompletion } from "./on-completion";
+import { ReadFileRequest, Requests } from "./request";
+import { getActionsMetadataProvider } from "./utils/action-metadata";
+import { TTLCache } from "./utils/cache";
+import { timeOperation } from "./utils/timer";
+import { valueProviders } from "./value-providers";
 
 export function initConnection(connection: Connection) {
   const documents: TextDocuments<TextDocument> = new TextDocuments(TextDocument);
@@ -72,6 +75,9 @@ export function initConnection(connection: Connection) {
         hoverProvider: true,
         documentLinkProvider: {
           resolveProvider: false
+        },
+        codeActionProvider: {
+          codeActionKinds: [CodeActionKind.QuickFix]
         }
       }
     };
@@ -110,15 +116,15 @@ export function initConnection(connection: Connection) {
       contextProviderConfig: contextProviders(client, repoContext, cache),
       actionsMetadataProvider: getActionsMetadataProvider(client, cache),
       fileProvider: getFileProvider(client, cache, repoContext?.workspaceUri, async path => {
-        return await connection.sendRequest(Requests.ReadFile, {path} satisfies ReadFileRequest);
+        return await connection.sendRequest(Requests.ReadFile, { path } satisfies ReadFileRequest);
       })
     };
 
     const result = await validate(textDocument, config);
-    await connection.sendDiagnostics({uri: textDocument.uri, diagnostics: result});
+    await connection.sendDiagnostics({ uri: textDocument.uri, diagnostics: result });
   }
 
-  connection.onCompletion(async ({position, textDocument}: TextDocumentPositionParams): Promise<CompletionItem[]> => {
+  connection.onCompletion(async ({ position, textDocument }: TextDocumentPositionParams): Promise<CompletionItem[]> => {
     return timeOperation(
       "completion",
       async () =>
@@ -133,14 +139,14 @@ export function initConnection(connection: Connection) {
     );
   });
 
-  connection.onHover(async ({position, textDocument}: HoverParams): Promise<Hover | null> => {
+  connection.onHover(async ({ position, textDocument }: HoverParams): Promise<Hover | null> => {
     return timeOperation("hover", async () => {
       const repoContext = repos.find(repo => textDocument.uri.startsWith(repo.workspaceUri));
       return await hover(getDocument(documents, textDocument), position, {
         descriptionProvider: descriptionProvider(client, cache),
         contextProviderConfig: repoContext && contextProviders(client, repoContext, cache),
         fileProvider: getFileProvider(client, cache, repoContext?.workspaceUri, async path => {
-          return await connection.sendRequest(Requests.ReadFile, {path});
+          return await connection.sendRequest(Requests.ReadFile, { path });
         })
       });
     });
@@ -153,11 +159,21 @@ export function initConnection(connection: Connection) {
     }
   });
 
-  connection.onDocumentLinks(async ({textDocument}: DocumentLinkParams): Promise<DocumentLink[] | null> => {
+  connection.onDocumentLinks(async ({ textDocument }: DocumentLinkParams): Promise<DocumentLink[] | null> => {
     const repoContext = repos.find(repo => textDocument.uri.startsWith(repo.workspaceUri));
     return documentLinks(getDocument(documents, textDocument), repoContext?.workspaceUri);
   });
 
+  connection.onCodeAction(async (params: CodeActionParams): Promise<CodeAction[]> => {
+    return timeOperation("codeAction", async () => {
+      return getCodeActions({
+        uri: params.textDocument.uri,
+        diagnostics: params.context.diagnostics,
+        only: params.context.only,
+      });
+    });
+  });
+
   // Make the text document manager listen on the connection
   // for open, change and close text document events
   documents.listen(connection);

languageservice/src/code-actions/index.ts

@@ -0,0 +1,55 @@
+import { CodeAction, CodeActionKind, Diagnostic } from "vscode-languageserver-types";
+import { CodeActionContext, CodeActionProvider } from "./types";
+import { quickfixProviders } from "./quickfix";
+
+// Aggregate all providers by kind
+const providersByKind: Map<string, CodeActionProvider[]> = new Map([
+  [CodeActionKind.QuickFix, quickfixProviders],
+  // [CodeActionKind. Refactor, refactorProviders],
+  // [CodeActionKind.Source, sourceProviders],
+  // etc
+]);
+
+export interface CodeActionConfig {
+  // TODO: actionsMetadataProvider, fileProvider, etc.
+}
+
+export interface CodeActionParams {
+  uri: string;
+  diagnostics: Diagnostic[];
+  only?: string[];
+}
+
+export function getCodeActions(params: CodeActionParams, config?: CodeActionConfig): CodeAction[] {
+  const actions: CodeAction[] = [];
+  const context: CodeActionContext = {
+    uri: params.uri,
+  };
+
+  // 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";

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

@@ -0,0 +1,67 @@
+import { CodeAction, TextEdit } from "vscode-languageserver-types";
+import { CodeActionContext, CodeActionProvider } from "../types";
+import { DiagnosticCode, MissingInputsDiagnosticData } from "../../validate-action";
+
+export const addMissingInputsProvider: CodeActionProvider = {
+  diagnosticCodes: [DiagnosticCode.MissingRequiredInputs],
+
+  createCodeAction(context, diagnostic): CodeAction | undefined {
+    const data = diagnostic.data as MissingInputsDiagnosticData | undefined;
+    if (!data) {
+      return undefined;
+    }
+
+    const edits = createInputEdits(data);
+    if (!edits) {
+      return undefined;
+    }
+
+    const inputNames = data.missingInputs.map(i => i.name).join(", ");
+
+    return {
+      title: `Add missing input${data.missingInputs.length > 1 ? "s" : ""}: ${inputNames}`,
+      edit: {
+        changes: {
+          [context.uri]: edits,
+        },
+      },
+    };
+  },
+};
+
+function createInputEdits(data: MissingInputsDiagnosticData): TextEdit[] | undefined {
+  const edits: TextEdit[] = [];
+
+  if (data.hasWithKey && data.withIndent !== undefined) {
+    // `with:` exists - use its indentation + 2 for inputs
+    const inputIndent = " ".repeat(data.withIndent + 2);
+
+    const inputLines = data.missingInputs.map(input => {
+      const value = input.default !== undefined ? input.default : '""';
+      return `${inputIndent}${input.name}: ${value}`;
+    });
+
+    edits.push({
+      range: { start: data.insertPosition, end: data.insertPosition },
+      newText: inputLines.map(line => line + "\n").join(""),
+    });
+  } else {
+    // No `with:` key - use step indentation for `with:`, +2 for inputs
+    const withIndent = " ".repeat(data.stepIndent + 2);
+    const inputIndent = " ".repeat(data.stepIndent + 4);
+
+    const inputLines = data.missingInputs.map(input => {
+      const value = input.default !== undefined ? input.default : '""';
+      return `${inputIndent}${input.name}: ${value}`;
+    });
+
+    const newText = [`${withIndent}with:\n`, ...inputLines.map(line => `${line}\n`)].join("");
+
+    edits.push({
+      range: { start: data.insertPosition, end: data.insertPosition },
+      newText,
+    });
+  }
+
+  return edits;
+}

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

@@ -0,0 +1,6 @@
+import { CodeActionProvider } from "../types";
+import { addMissingInputsProvider } from "./add-missing-inputs";
+
+export const quickfixProviders: CodeActionProvider[] = [
+  addMissingInputsProvider,
+];

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";
+import { ValidationConfig } from "../../validate";
+import { ActionMetadata, ActionReference } from "../../action";
+import { clearCache } from "../../utils/workflow-cache";
+
+// 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 +1,232 @@
+import * as fs from "fs";
+import * as path from "path";
+import { TextEdit } from "vscode-languageserver-types";
+import { TextDocument } from "vscode-languageserver-textdocument";
+import { validate, ValidationConfig } from "../../validate";
+import { getCodeActions, CodeActionParams } from "../index";
+
+// 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,
+      diagnostics: [diagnostic],
+    };
+
+    const actions = getCodeActions(params);
+    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.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/types.ts

@@ -0,0 +1,21 @@
+import { CodeAction, Diagnostic } from "vscode-languageserver-types";
+
+export interface CodeActionContext {
+  uri: string;
+  // TODO: add things like workflow template, parsed content, etc.
+}
+
+/**
+ * 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;
+}

languageservice/src/index.ts

@@ -1,7 +1,8 @@
-export {complete} from "./complete";
-export {ContextProviderConfig} from "./context-providers/config";
-export {documentLinks} from "./document-links";
-export {hover} from "./hover";
-export {Logger, LogLevel, registerLogger, setLogLevel} from "./log";
-export {validate, ValidationConfig, ActionsMetadataProvider} from "./validate";
-export {ValueProviderConfig, ValueProviderKind} from "./value-providers/config";
+export { complete } from "./complete";
+export { ContextProviderConfig } from "./context-providers/config";
+export { documentLinks } from "./document-links";
+export { hover } from "./hover";
+export { Logger, LogLevel, registerLogger, setLogLevel } from "./log";
+export { validate, ValidationConfig, ActionsMetadataProvider } from "./validate";
+export { ValueProviderConfig, ValueProviderKind } from "./value-providers/config";
+export { getCodeActions } from "./code-actions";

languageservice/src/validate-action.ts

@@ -1,12 +1,30 @@
-import {isMapping} from "@actions/workflow-parser";
-import {isActionStep} from "@actions/workflow-parser/model/type-guards";
-import {Step} from "@actions/workflow-parser/model/workflow-template";
-import {ScalarToken} from "@actions/workflow-parser/templates/tokens/scalar-token";
-import {TemplateToken} from "@actions/workflow-parser/templates/tokens/template-token";
-import {Diagnostic, DiagnosticSeverity} from "vscode-languageserver-types";
-import {parseActionReference} from "./action";
-import {mapRange} from "./utils/range";
-import {ValidationConfig} from "./validate";
+import { isMapping } from "@actions/workflow-parser";
+import { isActionStep } from "@actions/workflow-parser/model/type-guards";
+import { Step } from "@actions/workflow-parser/model/workflow-template";
+import { ScalarToken } from "@actions/workflow-parser/templates/tokens/scalar-token";
+import { TemplateToken } from "@actions/workflow-parser/templates/tokens/template-token";
+import { Diagnostic, DiagnosticSeverity } from "vscode-languageserver-types";
+import { ActionReference, parseActionReference } from "./action";
+import { mapRange } from "./utils/range";
+import { ValidationConfig } from "./validate";
+
+export const DiagnosticCode = {
+  MissingRequiredInputs: "missing-required-inputs",
+} as const;
+
+export interface MissingInputsDiagnosticData {
+  action: ActionReference;
+  missingInputs: Array<{
+    name: string;
+    default?: string;
+  }>;
+  hasWithKey: boolean;
+  // Indentation of the `with:` key if present, or the step's base indentation
+  withIndent?: number;
+  stepIndent: number;
+  // Position where new content should be inserted
+  insertPosition: { line: number; character: number };
+}
 
 export async function validateAction(
   diagnostics: Diagnostic[],
@@ -35,7 +53,7 @@ export async function validateAction(
 
   let withKey: ScalarToken | undefined;
   let withToken: TemplateToken | undefined;
-  for (const {key, value} of stepToken) {
+  for (const { key, value } of stepToken) {
     if (key.toString() === "with") {
       withKey = key;
       withToken = value;
@@ -45,7 +63,7 @@ export async function validateAction(
 
   const stepInputs = new Map<string, ScalarToken>();
   if (withToken && isMapping(withToken)) {
-    for (const {key} of withToken) {
+    for (const { key } of withToken) {
       stepInputs.set(key.toString(), key);
     }
   }
@@ -83,10 +101,32 @@ export async function validateAction(
       missingRequiredInputs.length === 1
         ? `Missing required input \`${missingRequiredInputs[0][0]}\``
         : `Missing required inputs: ${missingRequiredInputs.map(input => `\`${input[0]}\``).join(", ")}`;
+
+    const stepIndent = stepToken.range ? stepToken.range.start.column - 1 : 0; // 0-indexed
+    const withIndent = withKey?.range ? withKey.range.start.column - 1 : undefined;
+
+    const diagnosticData: MissingInputsDiagnosticData = {
+      action,
+      missingInputs: missingRequiredInputs.map(([name, input]) => ({
+        name,
+        default: input.default,
+      })),
+      hasWithKey: withKey !== undefined,
+      withIndent,
+      stepIndent,
+      insertPosition: withToken?.range
+        ? { line: withToken.range.end.line - 1, character: 0 }
+        : stepToken.range
+          ? { line: stepToken.range.end.line - 1, character: 0 }
+          : { line: 0, character: 0 },
+    };
+
     diagnostics.push({
       severity: DiagnosticSeverity.Error,
       range: mapRange((withKey || stepToken).range), // Highlight the whole step if we don't have a with key
-      message: message
+      message: message,
+      code: DiagnosticCode.MissingRequiredInputs,
+      data: diagnosticData
     });
   }
 }

languageservice/src/validate.actions.test.ts

@@ -1,11 +1,11 @@
-import {DiagnosticSeverity} from "vscode-languageserver-types";
-import {ActionMetadata, ActionReference} from "./action";
-import {registerLogger} from "./log";
-import {createDocument} from "./test-utils/document";
-import {TestLogger} from "./test-utils/logger";
-import {validate, ValidationConfig} from "./validate";
-import {ValueProviderKind} from "./value-providers/config";
-import {clearCache} from "./utils/workflow-cache";
+import { DiagnosticSeverity } from "vscode-languageserver-types";
+import { ActionMetadata, ActionReference } from "./action";
+import { registerLogger } from "./log";
+import { createDocument } from "./test-utils/document";
+import { TestLogger } from "./test-utils/logger";
+import { validate, ValidationConfig } from "./validate";
+import { ValueProviderKind } from "./value-providers/config";
+import { clearCache } from "./utils/workflow-cache";
 
 registerLogger(new TestLogger());
 
@@ -249,7 +249,28 @@ jobs:
             line: 7
           }
         },
-        severity: DiagnosticSeverity.Error
+        severity: DiagnosticSeverity.Error,
+        code: "missing-required-inputs",
+        data: {
+          action: {
+            name: "cache",
+            owner: "actions",
+            ref: "v1"
+          },
+          hasWithKey: true,
+          insertPosition: {
+            character: 0,
+            line: 9
+          },
+          missingInputs: [
+            {
+              default: undefined,
+              name: "path"
+            }
+          ],
+          stepIndent: 6,
+          withIndent: 6
+        }
       }
     ]);
   });
@@ -294,7 +315,32 @@ jobs:
             line: 7
           }
         },
-        severity: DiagnosticSeverity.Error
+        severity: DiagnosticSeverity.Error,
+        code: "missing-required-inputs",
+        data: {
+          action: {
+            name: "cache",
+            owner: "actions",
+            ref: "v1"
+          },
+          hasWithKey: true,
+          insertPosition: {
+            character: 0,
+            line: 9
+          },
+          missingInputs: [
+            {
+              default: undefined,
+              name: "path"
+            },
+            {
+              default: undefined,
+              name: "key"
+            }
+          ],
+          stepIndent: 6,
+          withIndent: 6
+        }
       }
     ]);
   });
@@ -323,7 +369,32 @@ jobs:
             line: 6
           }
         },
-        severity: DiagnosticSeverity.Error
+        severity: DiagnosticSeverity.Error,
+        code: "missing-required-inputs",
+        data: {
+          action: {
+            name: "cache",
+            owner: "actions",
+            ref: "v1"
+          },
+          hasWithKey: false,
+          insertPosition: {
+            character: 0,
+            line: 7
+          },
+          missingInputs: [
+            {
+              default: undefined,
+              name: "path"
+            },
+            {
+              default: undefined,
+              name: "key"
+            }
+          ],
+          stepIndent: 6,
+          withIndent: undefined
+        }
       }
     ]);
   });
@@ -344,7 +415,7 @@ jobs:
       "step-with": {
         kind: ValueProviderKind.AllowedValues,
         get: () => {
-          return Promise.resolve([{label: "repository", description: "Repository name with owner."}]);
+          return Promise.resolve([{ label: "repository", description: "Repository name with owner." }]);
         }
       }
     };