microsoft/TypeScript: 135 test baselines over 256 KiB

TypeScript's repository holds about 61,000 test baselines. A 256 KiB file_max_size rule found 135 larger than that, most of them test outputs that grew. The same run found trailing whitespace in 6 source files. This config was written to test alint; TypeScript doesn't use alint.

What alint found

.alint.yml

- id: ts-baseline-file-max-size
  kind: file_max_size
  paths:
    include: ["tests/baselines/reference/**/*"]
    exclude:
      - "tests/baselines/reference/projectOutput/**"
      - "tests/baselines/reference/api/**"
  max_bytes: 262144
  level: warning

⚠︎ warning ts-baseline-file-max-size

Of the test baselines, 135 are over 256 KiB, such as binaryArithmeticControlFlowGraphNotTooLarge.types.

.alint.yml

- id: ts-src-no-trailing-whitespace
  kind: no_trailing_whitespace
  paths:
    include: ["src/**/*.ts", "scripts/**/*.ts", "scripts/**/*.mjs", "scripts/**/*.cjs"]
    exclude: ["**/*.generated.*", "src/lib/*.generated.d.ts"]
  level: warning
  fix:
    file_trim_trailing_whitespace: {}

- id: ts-src-final-newline
  kind: final_newline
  paths:
    include: ["src/**/*.ts", "scripts/**/*.ts", "scripts/**/*.mjs", "scripts/**/*.cjs"]
    exclude: ["**/*.generated.*", "src/lib/*.generated.d.ts"]
  level: warning
  fix:
    file_append_final_newline: {}

⚠︎ warning ts-src-no-trailing-whitespace

Six source files have trailing whitespace, such as line 6549 of src/compiler/types.ts.

⚠︎ warning ts-src-final-newline

One source file has no final newline. alint fix handles both.

The bundled GitHub Actions rules (alint 0.16.1, on the workflows as of 7 May 2026) flag 5 action references that point at a branch, such as microsoft/TypeScript-Twoslash-Repro-Action@master, one in each of 5 workflows.

The config

The config checks what the lint gates depend on: the lint, format and knip scripts in package.json, the three dprint plugins and their version, and strict mode in the tsconfig files. It also checks line endings and whitespace in src/, as the .editorconfig asks. ESLint, dprint and knip run from command_idempotent rules.

.alint.yml

- id: ts-dprint-ts-plugin-version-agrees
  when: facts.has_dprint_config
  kind: cross_file_value_equals
  source:
    file: package.json
    extract:
      json: "$.devDependencies['@dprint/typescript']"
  targets:
    - file: .dprint.jsonc
      extract:
        regex: 'plugins\.dprint\.dev/typescript-([0-9]+\.[0-9]+\.[0-9]+)\.wasm'
  level: warning

The dprint TypeScript plugin's version is written twice, in package.json and in the plugin URL in .dprint.jsonc. This rule keeps them equal.

Speed

In the May run, on a full checkout, the rules that don't call other tools took 620 ms. Measured with hyperfine on a machine with 10 logical cores.

What stays outside alint

What needs TypeScript's syntax tree or the built compiler stays in the repository's tools:

the 9 custom ESLint rules, the baseline accept loop, and the generated files, which need their generators;
scripts/errorCheck.mjs, which checks that every diagnostic in diagnosticMessages.json appears in some error baseline. alint has no rule that requires each entry of a list to match somewhere;
the package-size check, which compares two git refs, and the browser and module-format checks, which run the built compiler.