ESM migration: Add .js extensions for node16 moduleResolution (#257)

Migrate expressions, workflow-parser, and languageservice packages to use
proper ESM imports with .js extensions that work with node16 moduleResolution.

Changes:
- Update tsconfig.build.json in each package to use module: node16 and
  moduleResolution: node16
- Add .js extensions to all relative import paths (Option B approach)
- Fix yaml internal type imports in workflow-parser by defining local types
- Add skipLibCheck to handle @types/node compatibility issues
- Add TypeScript 5.8.3 override in root package.json
- Add ESM migration plan documentation

The languageserver package is deferred due to test hang issues that need
further investigation.

Related #154 - Upgrade moduleResolution from node to node16 or nodenext
Related #110 - Published ESM code has imports without file extensions
Related #64 - expressions: ERR_MODULE_NOT_FOUND attempting to run example
Related #146 - Can not import @actions/workflow-parser

Test results:
- expressions: 1068 tests passed
- workflow-parser: 292 tests passed
- languageservice: 452 tests passed

* docs: update ESM migration plan with findings

- Update languageserver blocker: vscode-languageserver v8.0.2 lacks ESM
  exports (not a test hang issue)
- Document that Option B (manual .js extensions) was chosen over Option A
  due to ts-jest compatibility issues
- Add workaround for yaml package internal types (LinePos, NodeBase)
- Update migration status table with accurate reason for deferral
- Add skipLibCheck note for @types/node compatibility

workflow-parser/src/model/convert.test.ts

@@ -1,7 +1,7 @@
 /* eslint-disable @typescript-eslint/no-non-null-assertion */
-import {nullTrace} from "../test-utils/null-trace";
-import {parseWorkflow} from "../workflows/workflow-parser";
-import {convertWorkflowTemplate, ErrorPolicy} from "./convert";
+import {nullTrace} from "../test-utils/null-trace.js";
+import {parseWorkflow} from "../workflows/workflow-parser.js";
+import {convertWorkflowTemplate, ErrorPolicy} from "./convert.js";
 
 function serializeTemplate(template: unknown): unknown {
   return JSON.parse(JSON.stringify(template));

workflow-parser/src/model/convert.ts

@@ -1,15 +1,15 @@
-import {TemplateContext} from "../templates/template-context";
-import {TemplateToken, TemplateTokenError} from "../templates/tokens/template-token";
-import {FileProvider} from "../workflows/file-provider";
-import {parseFileReference} from "../workflows/file-reference";
-import {parseWorkflow} from "../workflows/workflow-parser";
-import {convertConcurrency} from "./converter/concurrency";
-import {convertOn} from "./converter/events";
-import {handleTemplateTokenErrors} from "./converter/handle-errors";
-import {convertJobs} from "./converter/jobs";
-import {convertReferencedWorkflow} from "./converter/referencedWorkflow";
-import {isReusableWorkflowJob} from "./type-guards";
-import {WorkflowTemplate} from "./workflow-template";
+import {TemplateContext} from "../templates/template-context.js";
+import {TemplateToken, TemplateTokenError} from "../templates/tokens/template-token.js";
+import {FileProvider} from "../workflows/file-provider.js";
+import {parseFileReference} from "../workflows/file-reference.js";
+import {parseWorkflow} from "../workflows/workflow-parser.js";
+import {convertConcurrency} from "./converter/concurrency.js";
+import {convertOn} from "./converter/events.js";
+import {handleTemplateTokenErrors} from "./converter/handle-errors.js";
+import {convertJobs} from "./converter/jobs.js";
+import {convertReferencedWorkflow} from "./converter/referencedWorkflow.js";
+import {isReusableWorkflowJob} from "./type-guards.js";
+import {WorkflowTemplate} from "./workflow-template.js";
 
 export enum ErrorPolicy {
   ReturnErrorsOnly,

workflow-parser/src/model/converter/concurrency.ts

@@ -1,7 +1,7 @@
-import {TemplateContext} from "../../templates/template-context";
-import {TemplateToken} from "../../templates/tokens/template-token";
-import {isString} from "../../templates/tokens/type-guards";
-import {ConcurrencySetting} from "../workflow-template";
+import {TemplateContext} from "../../templates/template-context.js";
+import {TemplateToken} from "../../templates/tokens/template-token.js";
+import {isString} from "../../templates/tokens/type-guards.js";
+import {ConcurrencySetting} from "../workflow-template.js";
 
 export function convertConcurrency(context: TemplateContext, token: TemplateToken): ConcurrencySetting {
   const result: ConcurrencySetting = {};

workflow-parser/src/model/converter/container.ts

@@ -1,7 +1,7 @@
-import {TemplateContext} from "../../templates/template-context";
-import {MappingToken, SequenceToken, StringToken, TemplateToken} from "../../templates/tokens";
-import {isString} from "../../templates/tokens/type-guards";
-import {Container, Credential} from "../workflow-template";
+import {TemplateContext} from "../../templates/template-context.js";
+import {MappingToken, SequenceToken, StringToken, TemplateToken} from "../../templates/tokens/index.js";
+import {isString} from "../../templates/tokens/type-guards.js";
+import {Container, Credential} from "../workflow-template.js";
 
 export function convertToJobContainer(context: TemplateContext, container: TemplateToken): Container | undefined {
   let image: StringToken | undefined;

workflow-parser/src/model/converter/cron.test.ts

@@ -1,4 +1,4 @@
-import {isValidCron, getCronDescription, hasCronIntervalLessThan5Minutes} from "./cron";
+import {isValidCron, getCronDescription, hasCronIntervalLessThan5Minutes} from "./cron.js";
 
 describe("cron", () => {
   describe("valid cron", () => {

workflow-parser/src/model/converter/cron.ts

@@ -1,6 +1,6 @@
 import cronstrue from "cronstrue";
 
-import {MONTH_RANGE, HOUR_RANGE, MINUTE_RANGE, DOM_RANGE, DOW_RANGE} from "./cron-constants";
+import {MONTH_RANGE, HOUR_RANGE, MINUTE_RANGE, DOM_RANGE, DOW_RANGE} from "./cron-constants.js";
 
 type Range = {
   min: number;

workflow-parser/src/model/converter/events.ts

@@ -1,9 +1,9 @@
-import {TemplateContext} from "../../templates/template-context";
-import {MappingToken} from "../../templates/tokens/mapping-token";
-import {SequenceToken} from "../../templates/tokens/sequence-token";
-import {TemplateToken} from "../../templates/tokens/template-token";
-import {isLiteral, isMapping, isSequence, isString} from "../../templates/tokens/type-guards";
-import {TokenType} from "../../templates/tokens/types";
+import {TemplateContext} from "../../templates/template-context.js";
+import {MappingToken} from "../../templates/tokens/mapping-token.js";
+import {SequenceToken} from "../../templates/tokens/sequence-token.js";
+import {TemplateToken} from "../../templates/tokens/template-token.js";
+import {isLiteral, isMapping, isSequence, isString} from "../../templates/tokens/type-guards.js";
+import {TokenType} from "../../templates/tokens/types.js";
 import {
   BranchFilterConfig,
   EventsConfig,
@@ -14,11 +14,11 @@ import {
   TypesFilterConfig,
   VersionsFilterConfig,
   WorkflowFilterConfig
-} from "../workflow-template";
-import {isValidCron} from "./cron";
-import {convertStringList} from "./string-list";
-import {convertEventWorkflowCall} from "./workflow-call";
-import {convertEventWorkflowDispatchInputs} from "./workflow-dispatch";
+} from "../workflow-template.js";
+import {isValidCron} from "./cron.js";
+import {convertStringList} from "./string-list.js";
+import {convertEventWorkflowCall} from "./workflow-call.js";
+import {convertEventWorkflowDispatchInputs} from "./workflow-dispatch.js";
 
 export function convertOn(context: TemplateContext, token: TemplateToken): EventsConfig {
   if (isLiteral(token)) {

workflow-parser/src/model/converter/handle-errors.ts

@@ -1,5 +1,5 @@
-import {TemplateContext} from "../../templates/template-context";
-import {TemplateToken, TemplateTokenError} from "../../templates/tokens/template-token";
+import {TemplateContext} from "../../templates/template-context.js";
+import {TemplateToken, TemplateTokenError} from "../../templates/tokens/template-token.js";
 
 export function handleTemplateTokenErrors<TResult>(
   root: TemplateToken,

workflow-parser/src/model/converter/id-builder.test.ts

@@ -1,4 +1,4 @@
-import {IdBuilder} from "./id-builder";
+import {IdBuilder} from "./id-builder.js";
 
 function build(...segments: string[]): string {
   const builder = new IdBuilder();

workflow-parser/src/model/converter/if-condition.ts

@@ -1,9 +1,9 @@
 import {Lexer, Parser} from "@actions/expressions";
 import {Binary, Expr, FunctionCall, Grouping, IndexAccess, Logical, Unary} from "@actions/expressions/ast";
-import {DefinitionInfo} from "../../templates/schema/definition-info";
-import {splitAllowedContext} from "../../templates/allowed-context";
-import {TemplateContext} from "../../templates/template-context";
-import {BasicExpressionToken, ExpressionToken, TemplateToken} from "../../templates/tokens";
+import {DefinitionInfo} from "../../templates/schema/definition-info.js";
+import {splitAllowedContext} from "../../templates/allowed-context.js";
+import {TemplateContext} from "../../templates/template-context.js";
+import {BasicExpressionToken, ExpressionToken, TemplateToken} from "../../templates/tokens/index.js";
 
 /**
  * Ensures a condition expression contains a status function call.

workflow-parser/src/model/converter/job.ts

@@ -1,15 +1,21 @@
-import {TemplateContext} from "../../templates/template-context";
-import {BasicExpressionToken, MappingToken, ScalarToken, StringToken, TemplateToken} from "../../templates/tokens";
-import {isSequence, isString} from "../../templates/tokens/type-guards";
-import {Step, WorkflowJob} from "../workflow-template";
-import {convertToIfCondition} from "./if-condition";
-import {convertConcurrency} from "./concurrency";
-import {convertToJobContainer, convertToJobServices} from "./container";
-import {handleTemplateTokenErrors} from "./handle-errors";
-import {IdBuilder} from "./id-builder";
-import {convertToActionsEnvironmentRef} from "./job/environment";
-import {convertRunsOn} from "./job/runs-on";
-import {convertSteps} from "./steps";
+import {TemplateContext} from "../../templates/template-context.js";
+import {
+  BasicExpressionToken,
+  MappingToken,
+  ScalarToken,
+  StringToken,
+  TemplateToken
+} from "../../templates/tokens/index.js";
+import {isSequence, isString} from "../../templates/tokens/type-guards.js";
+import {Step, WorkflowJob} from "../workflow-template.js";
+import {convertToIfCondition} from "./if-condition.js";
+import {convertConcurrency} from "./concurrency.js";
+import {convertToJobContainer, convertToJobServices} from "./container.js";
+import {handleTemplateTokenErrors} from "./handle-errors.js";
+import {IdBuilder} from "./id-builder.js";
+import {convertToActionsEnvironmentRef} from "./job/environment.js";
+import {convertRunsOn} from "./job/runs-on.js";
+import {convertSteps} from "./steps.js";
 
 export function convertJob(context: TemplateContext, jobKey: StringToken, token: MappingToken): WorkflowJob {
   const error = new IdBuilder().tryAddKnownId(jobKey.value);

workflow-parser/src/model/converter/job/environment.ts

@@ -1,7 +1,7 @@
-import {TemplateContext} from "../../../templates/template-context";
-import {TemplateToken} from "../../../templates/tokens/template-token";
-import {isScalar} from "../../../templates/tokens/type-guards";
-import {ActionsEnvironmentReference} from "../../workflow-template";
+import {TemplateContext} from "../../../templates/template-context.js";
+import {TemplateToken} from "../../../templates/tokens/template-token.js";
+import {isScalar} from "../../../templates/tokens/type-guards.js";
+import {ActionsEnvironmentReference} from "../../workflow-template.js";
 
 export function convertToActionsEnvironmentRef(
   context: TemplateContext,

workflow-parser/src/model/converter/job/inputs.ts

@@ -1,6 +1,6 @@
-import {TemplateContext} from "../../../templates/template-context";
-import {MappingToken, TemplateToken} from "../../../templates/tokens";
-import {ReusableWorkflowJob} from "../../workflow-template";
+import {TemplateContext} from "../../../templates/template-context.js";
+import {MappingToken, TemplateToken} from "../../../templates/tokens/index.js";
+import {ReusableWorkflowJob} from "../../workflow-template.js";
 
 type TokenMap = Map<string, [key: string, value: TemplateToken]>;
 

workflow-parser/src/model/converter/job/runs-on.ts

@@ -1,6 +1,6 @@
-import {TemplateContext} from "../../../templates/template-context";
-import {TemplateToken} from "../../../templates/tokens";
-import {isMapping, isString, isSequence} from "../../../templates/tokens/type-guards";
+import {TemplateContext} from "../../../templates/template-context.js";
+import {TemplateToken} from "../../../templates/tokens/index.js";
+import {isMapping, isString, isSequence} from "../../../templates/tokens/type-guards.js";
 
 type RunsOn = {
   labels: Set<string>;

workflow-parser/src/model/converter/job/secrets.ts

@@ -1,7 +1,7 @@
-import {TemplateContext} from "../../../templates/template-context";
-import {NullToken} from "../../../templates/tokens";
-import {ReusableWorkflowJob} from "../../workflow-template";
-import {createTokenMap} from "./inputs";
+import {TemplateContext} from "../../../templates/template-context.js";
+import {NullToken} from "../../../templates/tokens/index.js";
+import {ReusableWorkflowJob} from "../../workflow-template.js";
+import {createTokenMap} from "./inputs.js";
 
 export function convertWorkflowJobSecrets(context: TemplateContext, job: ReusableWorkflowJob) {
   // No validation if job passes all secrets

workflow-parser/src/model/converter/jobs.ts

@@ -1,10 +1,10 @@
-import {TemplateContext} from "../../templates/template-context";
-import {StringToken} from "../../templates/tokens";
-import {TemplateToken} from "../../templates/tokens/template-token";
-import {isMapping} from "../../templates/tokens/type-guards";
-import {WorkflowJob} from "../workflow-template";
-import {handleTemplateTokenErrors} from "./handle-errors";
-import {convertJob} from "./job";
+import {TemplateContext} from "../../templates/template-context.js";
+import {StringToken} from "../../templates/tokens/index.js";
+import {TemplateToken} from "../../templates/tokens/template-token.js";
+import {isMapping} from "../../templates/tokens/type-guards.js";
+import {WorkflowJob} from "../workflow-template.js";
+import {handleTemplateTokenErrors} from "./handle-errors.js";
+import {convertJob} from "./job.js";
 
 type nodeInfo = {
   name: string;

workflow-parser/src/model/converter/referencedWorkflow.ts

@@ -1,11 +1,11 @@
-import {TemplateContext} from "../../templates/template-context";
-import {TemplateToken} from "../../templates/tokens";
-import {TokenType} from "../../templates/tokens/types";
-import {ReusableWorkflowJob} from "../workflow-template";
-import {handleTemplateTokenErrors} from "./handle-errors";
-import {convertWorkflowJobInputs} from "./job/inputs";
-import {convertWorkflowJobSecrets} from "./job/secrets";
-import {convertJobs} from "./jobs";
+import {TemplateContext} from "../../templates/template-context.js";
+import {TemplateToken} from "../../templates/tokens/index.js";
+import {TokenType} from "../../templates/tokens/types.js";
+import {ReusableWorkflowJob} from "../workflow-template.js";
+import {handleTemplateTokenErrors} from "./handle-errors.js";
+import {convertWorkflowJobInputs} from "./job/inputs.js";
+import {convertWorkflowJobSecrets} from "./job/secrets.js";
+import {convertJobs} from "./jobs.js";
 
 export function convertReferencedWorkflow(
   context: TemplateContext,

workflow-parser/src/model/converter/steps.ts

@@ -1,11 +1,17 @@
-import {TemplateContext} from "../../templates/template-context";
-import {BasicExpressionToken, MappingToken, ScalarToken, StringToken, TemplateToken} from "../../templates/tokens";
-import {isSequence} from "../../templates/tokens/type-guards";
-import {isActionStep} from "../type-guards";
-import {convertToIfCondition} from "./if-condition";
-import {ActionStep, Step} from "../workflow-template";
-import {handleTemplateTokenErrors} from "./handle-errors";
-import {IdBuilder} from "./id-builder";
+import {TemplateContext} from "../../templates/template-context.js";
+import {
+  BasicExpressionToken,
+  MappingToken,
+  ScalarToken,
+  StringToken,
+  TemplateToken
+} from "../../templates/tokens/index.js";
+import {isSequence} from "../../templates/tokens/type-guards.js";
+import {isActionStep} from "../type-guards.js";
+import {convertToIfCondition} from "./if-condition.js";
+import {ActionStep, Step} from "../workflow-template.js";
+import {handleTemplateTokenErrors} from "./handle-errors.js";
+import {IdBuilder} from "./id-builder.js";
 
 export function convertSteps(context: TemplateContext, steps: TemplateToken): Step[] {
   if (!isSequence(steps)) {

workflow-parser/src/model/converter/string-list.ts

@@ -1,4 +1,4 @@
-import {SequenceToken} from "../../templates/tokens/sequence-token";
+import {SequenceToken} from "../../templates/tokens/sequence-token.js";
 
 export function convertStringList(name: string, token: SequenceToken): string[] {
   const result = [] as string[];

workflow-parser/src/model/converter/workflow-call.ts

@@ -1,9 +1,9 @@
-import {TemplateContext} from "../../templates/template-context";
-import {MappingToken, TemplateToken} from "../../templates/tokens";
-import {isMapping} from "../../templates/tokens/type-guards";
-import {SecretConfig, WorkflowCallConfig, InputConfig, InputType} from "../workflow-template";
-import {convertStringList} from "./string-list";
-import {ScalarToken} from "../../templates/tokens/scalar-token";
+import {TemplateContext} from "../../templates/template-context.js";
+import {MappingToken, TemplateToken} from "../../templates/tokens/index.js";
+import {isMapping} from "../../templates/tokens/type-guards.js";
+import {SecretConfig, WorkflowCallConfig, InputConfig, InputType} from "../workflow-template.js";
+import {convertStringList} from "./string-list.js";
+import {ScalarToken} from "../../templates/tokens/scalar-token.js";
 
 export function convertEventWorkflowCall(context: TemplateContext, token: MappingToken): WorkflowCallConfig {
   const result: WorkflowCallConfig = {};

workflow-parser/src/model/converter/workflow-dispatch.ts

@@ -1,8 +1,8 @@
-import {TemplateContext} from "../../templates/template-context";
-import {MappingToken} from "../../templates/tokens/mapping-token";
-import {ScalarToken} from "../../templates/tokens/scalar-token";
-import {InputConfig, InputType, WorkflowDispatchConfig} from "../workflow-template";
-import {convertStringList} from "./string-list";
+import {TemplateContext} from "../../templates/template-context.js";
+import {MappingToken} from "../../templates/tokens/mapping-token.js";
+import {ScalarToken} from "../../templates/tokens/scalar-token.js";
+import {InputConfig, InputType, WorkflowDispatchConfig} from "../workflow-template.js";
+import {convertStringList} from "./string-list.js";
 
 export function convertEventWorkflowDispatchInputs(
   context: TemplateContext,

workflow-parser/src/model/type-guards.ts

@@ -1,4 +1,4 @@
-import {ActionStep, Job, ReusableWorkflowJob, RunStep, Step, WorkflowJob} from "./workflow-template";
+import {ActionStep, Job, ReusableWorkflowJob, RunStep, Step, WorkflowJob} from "./workflow-template.js";
 
 export function isRunStep(step: Step): step is RunStep {
   return (step as RunStep).run !== undefined;

workflow-parser/src/model/workflow-template.ts

@@ -5,7 +5,7 @@ import {
   SequenceToken,
   StringToken,
   TemplateToken
-} from "../templates/tokens";
+} from "../templates/tokens/index.js";
 
 export type WorkflowTemplate = {
   events: EventsConfig;