ci: Measure the type-check budget with TypeScript 7

[ntucker]

Requested by Nathaniel · project thread

Follow-up to #4182.

Motivation

Before: yarn check:typeperf measured instantiations with the TypeScript 6 JS API (require('typescript') resolves to @typescript/typescript6), while the repo builds and type-checks with TypeScript 7 (@typescript/native).

After: it measures with the same TypeScript 7 tsc the repo builds with, so the budget tracks the compiler users and CI actually run.

Solution

• check.mjs spawns the repo's tsc (the bin yarn puts on PATH) with --extendedDiagnostics --pretty false per fixture and reads the Instantiations: and Total time: lines. A non-zero exit fails the fixture and prints the first 10 errors; output with no instantiation count fails too. The version comes from tsc --version.
• Windows support is kept: the shell is used only on win32, and the tsconfig path is passed relative to the repo root so a checkout path with spaces can't be split. The "has no budget" failure from ci: Add a type-check perf budget and path-type fuzz check #4182 is unchanged.
• budget.json is a new TypeScript 7.0.2 baseline, re-recorded with --update. These numbers are not comparable to the old TS 6 ones. TS 7 counts are within 4% of TS 6 for every fixture except schemas (99,251 → 109,095, +9.9%). That's a compiler difference, not a change to our types: master's types are unchanged in this PR.
• Counts are deterministic across runs (verified 3× per fixture, and with --checkers 1 / --singleThreaded, since each fixture is one source file).
• The full check runs in about 12s locally (each TS 7 fixture checks roughly 2.5× faster than TS 6).

Validated: yarn check:typeperf passes; injecting a type error into a fixture fails with tsc exited with 1, 1 type errors and the error line; deleting a fixture's budget fails with has no budget.

Open questions

Running fixtures in parallel would cut the check to about 5–6s on 4 cores without changing counts, but makes the printed times noisier. I left it sequential for now.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QFo5AAtZp18HcwiXBqBDEZ

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Generated by Claude Code

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Note

Low Risk
Changes only the typeperf CI script and recorded budgets; library types and runtime behavior are untouched.

Overview
yarn check:typeperf now measures instantiation counts with the same TypeScript 7 tsc the repo builds with (@typescript/native), instead of the TypeScript 6 programmatic API.

check.mjs spawns tsc per fixture with --extendedDiagnostics, parses Instantiations and Total time from stdout, and records the compiler version from tsc --version. Non-zero exits and missing instantiation output fail the check; Windows still uses a shell only on win32 and passes a relative tsconfig path.

budget.json is re-recorded for TypeScript 7.0.2 — counts are not comparable to the old TS 6 baseline. The README notes that compiler upgrades require --update when counts shift.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.09%. Comparing base (97b3016) to head (2ee0f08).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4192   +/-   ##
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  Coverage   98.09%   98.09%           
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  Files         165      165           
  Lines        3143     3143           
  Branches      625      625           
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  Misses         18       18           
  Partials       42       42           

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