Fix missing lib files in reused programs

[jakebailey]

Fixes #63228

I should have noticed this in the baselines from my original change, but I did not.

This should be cherry-picked to 6.0.

[jakebailey]

@typescript-bot pack this

[typescript-bot]

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
pack this	✅ Started	✅ Results

[typescript-bot]

Hey @jakebailey, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/167413/artifacts?artifactName=tgz&fileId=9172AA0B40779F1AC39448730BC86E547DE9294E1DF8B85C9C1E2347B88C9CF202&fileName=/typescript-6.0.0-insiders.20260311.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@6.0.0-pr-63239-2".;

[Copilot]

Pull request overview

Fixes a regression in program-structure reuse where default library files were not being tracked as default libs in the reused program, leading to incorrect behavior in APIs like isSourceFileDefaultLibrary and downstream watch/tsserver outputs (issue #63228).

Changes:

• Re-populate libFiles during complete structure reuse so isSourceFileDefaultLibrary remains accurate.
• Add a unit test covering isSourceFileDefaultLibrary after ts.createProgram(..., oldProgram) reuse.
• Update multiple tsserver/tsc-watch baselines to reflect corrected default-lib classification.

Reviewed changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/baselines/reference/tsserver/compileOnSave/emit-in-project.js	Baseline update reflecting corrected default-lib handling in compileOnSave output
tests/baselines/reference/tsserver/compileOnSave/emit-in-project-with-module.js	Baseline update reflecting corrected default-lib handling in compileOnSave output
tests/baselines/reference/tsserver/compileOnSave/configProjects-global-file-shape-changed.js	Baseline update reflecting corrected default-lib handling in compileOnSave output
tests/baselines/reference/tscWatch/watchEnvironment/watchFile/using-fixed-chunk-size-polling.js	Baseline update reflecting corrected default-lib classification in watch output
tests/baselines/reference/tscWatch/watchEnvironment/watchFile/using-dynamic-priority-polling.js	Baseline update reflecting corrected default-lib classification in watch output
tests/baselines/reference/tscWatch/watchEnvironment/fsEvent-for-change-is-repeated.js	Baseline update reflecting corrected default-lib classification in watch output
tests/baselines/reference/tscWatch/programUpdates/when-skipLibCheck-and-skipDefaultLibCheck-changes.js	Baseline update reflecting corrected default-lib handling when check options change
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-non-module-file-changes/with-skipLibCheck.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-non-module-file-changes/with-skipDefaultLibCheck.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-non-module-file-changes/with-default-options.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-module-file-with-global-definitions-changes/with-skipLibCheck.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-module-file-with-global-definitions-changes/with-skipDefaultLibCheck.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/updates-errors-in-lib-file/when-module-file-with-global-definitions-changes/with-default-options.js	Baseline update reflecting corrected default-lib classification in incremental program updates
tests/baselines/reference/tscWatch/programUpdates/should-reflect-change-in-config-file.js	Baseline update reflecting corrected default-lib classification in program updates
tests/baselines/reference/tscWatch/programUpdates/handle-recreated-files-correctly.js	Baseline update reflecting corrected default-lib classification in program updates
tests/baselines/reference/tscWatch/noEmit/multiFile/semantic-errors.js	Baseline update reflecting corrected default-lib classification in noEmit watch output
tests/baselines/reference/tscWatch/noEmit/multiFile/semantic-errors-with-incremental.js	Baseline update reflecting corrected default-lib classification in noEmit incremental watch output
tests/baselines/reference/tscWatch/noEmit/multiFile/dts-errors.js	Baseline update reflecting corrected default-lib classification in watch output
tests/baselines/reference/tscWatch/noEmit/multiFile/dts-errors-without-dts-enabled.js	Baseline update reflecting corrected default-lib classification in watch output
tests/baselines/reference/tscWatch/noEmit/multiFile/dts-errors-without-dts-enabled-with-incremental.js	Baseline update reflecting corrected default-lib classification in incremental watch output
tests/baselines/reference/tscWatch/noEmit/multiFile/dts-errors-with-incremental.js	Baseline update reflecting corrected default-lib classification in incremental watch output
tests/baselines/reference/tscWatch/emit/when-module-emit-is-specified-as-node/when-instead-of-filechanged-recursive-directory-watcher-is-invoked.js	Baseline update reflecting corrected default-lib classification in emit watch output
tests/baselines/reference/tscWatch/emit/emit-with-outFile-or-out-setting/config-has-out.js	Baseline update reflecting corrected default-lib classification in emit watch output
tests/baselines/reference/tscWatch/emit/emit-with-outFile-or-out-setting/config-does-not-have-out-or-outFile.js	Baseline update reflecting corrected default-lib classification in emit watch output
tests/baselines/reference/tscWatch/emit/emit-for-configured-projects/should-return-all-files-if-a-global-file-changed-shape.js	Baseline update reflecting corrected default-lib classification in configured-project emit watch output
tests/baselines/reference/tscWatch/emit/emit-file-content/handles-new-lines-lineFeed.js	Baseline update reflecting corrected default-lib classification in emit watch output
tests/baselines/reference/tscWatch/emit/emit-file-content/handles-new-lines-carriageReturn-lineFeed.js	Baseline update reflecting corrected default-lib classification in emit watch output
tests/baselines/reference/tscWatch/emit/emit-file-content/file-is-deleted-and-created-as-part-of-change.js	Baseline update reflecting corrected default-lib classification in emit watch output
src/testRunner/unittests/reuseProgramStructure.ts	Adds a unit test for isSourceFileDefaultLibrary behavior after program reuse
src/compiler/program.ts	Copies default-lib membership (libFiles) during complete structure reuse

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[Copilot]

This test intends to validate behavior specifically after program structure reuse, but it doesn’t currently assert that reuse actually happened. If reuse heuristics change (e.g. structure falls back to SafeModules/Not), the test could pass without exercising the regression. Consider asserting program2.structureIsReused is Completely (or at least asserting the lib SourceFile object was reused) before checking isSourceFileDefaultLibrary.