Fixed `anyFunctionType` leak by Andarist · Pull Request #64131 · microsoft/TypeScript

Mateusz Burzyński (Andarist) · 2026-09-02T09:49:29Z

recreates #61980
fixes #61979

Copilot

🟡 Changes recommended

Two regression cases duplicate fn coverage instead of exercising the intended fn2 scenarios.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Fixes cached anyFunctionType leakage during contextual return-type computation.

Changes:

Recomputes return types without CheckModeSkipContextSensitive.
Adds compiler regression cases and diagnostic/type/symbol baselines.

File summaries

File	Description
`tsc/internal/checker/checker.go`	Prevents context-sensitive return types from leaking `anyFunctionType`.
`tsc/testdata/tests/cases/compiler/contextualTypingGenericFunction2.ts`	Adds regression scenarios.
`tsc/testdata/baselines/reference/compiler/contextualTypingGenericFunction2.errors.txt`	Records expected diagnostics.
`tsc/testdata/baselines/reference/compiler/contextualTypingGenericFunction2.types`	Records inferred types.
`tsc/testdata/baselines/reference/compiler/contextualTypingGenericFunction2.symbols`	Records symbol information.

Review details

Suppressed comments (1)

tsc/testdata/tests/cases/compiler/contextualTypingGenericFunction2.ts:57

This calls fn again and duplicates result3, leaving the corresponding inferred incompatible-return scenario untested for fn2. Change this call to fn2 and regenerate the baselines.

export const result6 = fn({

Files reviewed: 5/5 changed files
Comments generated: 1
Review effort level: Balanced

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Jake Bailey (jakebailey) · 2026-09-02T17:30:46Z

TypeScript Bot (@typescript-bot) test it

typescript-automation · 2026-09-02T17:30:51Z

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

Command	Status	Results
`test top400`	✅ Started	✅ Results
`user test this`	✅ Started	✅ Results
`run dt`	✅ Started
`perf test this faster`	✅ Started	👀 Results

typescript-automation · 2026-09-02T17:52:49Z

Jake Bailey (@jakebailey) Here are the results of running the user tests with tsc comparing main and refs/pull/64131/merge:

There were infrastructure failures potentially unrelated to your change:

2 instances of "Package install failed"
1 instance of "Git clone failed"

Otherwise...

Everything looks good!

typescript-automation · 2026-09-02T17:59:05Z

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_115,480	_115,480	_~	_~	_~	_{p=1.000 n=12}
_Types	_96,945	_96,945	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{148,641k (± 0.61%)}	_{149,207k (± 0.53%)}	_~	_146,985k	_150,758k	_{p=0.378 n=12}
_{Memory Allocs}	_{2,271,259 (± 0.00%)}	_{2,271,298 (± 0.00%)}	_~	_2,271,116	_2,271,479	_{p=0.443 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.040s (± 2.52%)}	_{0.040s (± 3.66%)}	_~	_0.038s	_0.046s	_{p=0.142 n=12}
_{Bind Time}	_{0.012s (±12.23%)}	_{0.011s (± 7.97%)}	_~	_0.010s	_0.014s	_{p=0.204 n=12}
_{Check Time}	_{0.495s (± 0.64%)}	_{0.497s (± 1.21%)}	_~	_0.486s	_0.519s	_{p=0.765 n=12}
_{Emit Time}	_{0.273s (± 1.98%)}	_{0.273s (± 2.70%)}	_~	_0.259s	_0.295s	_{p=0.722 n=12}
_{Total Time}	_{0.827s (± 0.56%)}	_{0.827s (± 1.26%)}	_~	_0.807s	_0.854s	_{p=0.809 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{846,830 (± 0.06%)}	_{847,166 (± 0.08%)}	_~	_845,358	_848,915	_{p=0.443 n=12}
_Types	_{249,853 (± 0.00%)}	_{249,852 (± 0.00%)}	_~	_249,849	_249,861	_{p=0.232 n=12}
_{Memory Used}	_{793,209k (± 0.05%)}	_{793,637k (± 0.07%)}	_~	_792,202k	_795,224k	_{p=0.266 n=12}
_{Memory Allocs}	_{12,953,477 (± 0.04%)}	_{12,958,431 (± 0.03%)}	_{+4,954 (+ 0.04%)}	_12,950,397	_12,972,182	_{p=0.006 n=12}
_{Config Time}	_0.016s	_0.016s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.271s (± 2.24%)}	_{0.275s (± 4.12%)}	_~	_0.245s	_0.302s	_{p=0.541 n=12}
_{Bind Time}	_{0.061s (± 5.71%)}	_{0.071s (±19.96%)}	_~	_0.057s	_0.115s	_{p=0.508 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.635s (± 1.41%)}	_{1.642s (± 1.26%)}	_~	_1.609s	_1.697s	_{p=0.369 n=12}
_{Total Time}	_{1.999s (± 1.30%)}	_{2.023s (± 1.61%)}	_~	_1.974s	_2.109s	_{p=0.213 n=12}
_{mui-docs - native}
_Errors	_{11,273 (± 0.04%)}	_{11,274 (± 0.05%)}	_~	_11,252	_11,281	_{p=0.414 n=12}
_Symbols	_4,477,906	_4,477,906	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,550,100	_1,550,100	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,373,575k (± 0.03%)}	_{5,373,325k (± 0.03%)}	_~	_5,368,976k	_5,377,193k	_{p=0.713 n=12}
_{Memory Allocs}	_{45,791,719 (± 0.04%)}	_{45,795,085 (± 0.05%)}	_~	_45,722,945	_45,868,023	_{p=0.843 n=12}
_{Config Time}	_{0.016s (± 2.12%)}	_{0.016s (± 1.98%)}	_~	_0.015s	_0.016s	_{p=0.680 n=12}
_{Parse Time}	_{0.542s (± 1.57%)}	_{0.548s (± 1.96%)}	_~	_0.505s	_0.565s	_{p=0.155 n=12}
_{Bind Time}	_{0.002s (± 8.72%)}	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{15.812s (± 0.37%)}	_{15.779s (± 0.29%)}	_~	_15.688s	_15.885s	_{p=0.418 n=12}
_{Emit Time}	_{0.447s (± 2.59%)}	_{0.451s (± 2.57%)}	_~	_0.430s	_0.471s	_{p=0.764 n=12}
_{Total Time}	_{17.568s (± 0.39%)}	_{17.526s (± 0.38%)}	_~	_17.394s	_17.670s	_{p=0.443 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,394,252	_1,394,252	_~	_~	_~	_{p=1.000 n=12}
_Types	_443,418	_443,418	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,648,691k (± 0.24%)}	_{1,650,821k (± 0.23%)}	_~	_1,642,610k	_1,663,420k	_{p=0.630 n=12}
_{Memory Allocs}	_{97,061,460 (± 0.04%)}	_{97,081,694 (± 0.03%)}	_~	_97,001,212	_97,169,237	_{p=0.630 n=12}
_{Config Time}	_{0.004s (±18.29%)}	_{0.003s (±14.60%)}	_~	_0.002s	_0.004s	_{p=0.457 n=12}
_{Parse Time}	_{0.194s (± 3.07%)}	_{0.200s (± 1.94%)}	_{+0.006s (+ 3.14%)}	_0.190s	_0.209s	_{p=0.032 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.817s (± 0.46%)}	_{1.815s (± 0.25%)}	_~	_1.799s	_1.825s	_{p=0.434 n=12}
_{Emit Time}	_{0.281s (± 5.06%)}	_{0.290s (± 4.72%)}	_~	_0.244s	_0.314s	_{p=0.355 n=12}
_{Total Time}	_{24.851s (± 0.62%)}	_{24.974s (± 0.72%)}	_~	_24.438s	_25.497s	_{p=0.291 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_337,531	_337,531	_~	_~	_~	_{p=1.000 n=12}
_Types	_198,830	_198,830	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{319,662k (± 0.08%)}	_{319,566k (± 0.02%)}	_~	_319,403k	_319,779k	_{p=0.944 n=12}
_{Memory Allocs}	_{4,673,374 (± 0.01%)}	_{4,673,238 (± 0.01%)}	_~	_4,671,985	_4,674,062	_{p=0.755 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.117s (± 3.46%)}	_{0.116s (± 4.43%)}	_~	_0.100s	_0.130s	_{p=0.744 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.053s (± 0.59%)}	_{1.052s (± 0.32%)}	_~	_1.046s	_1.066s	_{p=0.765 n=12}
_{Emit Time}	_{0.143s (±12.42%)}	_{0.137s (±13.68%)}	_~	_0.097s	_0.167s	_{p=0.578 n=12}
_{Total Time}	_{1.367s (± 1.14%)}	_{1.357s (± 1.03%)}	_~	_1.317s	_1.380s	_{p=0.434 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_305,179	_305,179	_~	_~	_~	_{p=1.000 n=12}
_Types	_181,876	_181,876	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{277,172k (± 0.02%)}	_{277,180k (± 0.02%)}	_~	_277,015k	_277,279k	_{p=0.551 n=12}
_{Memory Allocs}	_{1,641,883 (± 0.01%)}	_{1,641,958 (± 0.01%)}	_~	_1,641,669	_1,642,261	_{p=0.514 n=12}
_{Config Time}	_0.000s	_{0.000s (±146.91%)}	_~	_0.000s	_0.001s	_{p=0.478 n=12}
_{Parse Time}	_{0.102s (± 4.46%)}	_{0.101s (± 3.64%)}	_~	_0.091s	_0.109s	_{p=0.598 n=12}
_{Bind Time}	_{0.037s (±10.27%)}	_{0.035s (± 9.26%)}	_~	_0.029s	_0.045s	_{p=0.502 n=12}
_{Check Time}	_{0.839s (± 0.60%)}	_{0.834s (± 0.76%)}	_~	_0.819s	_0.847s	_{p=0.339 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.992s (± 0.98%)}	_{0.985s (± 0.54%)}	_~	_0.971s	_0.998s	_{p=0.416 n=12}
_{vscode - native}
_Errors	₃₄₇	₃₄₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_8,265,607	_8,265,607	_~	_~	_~	_{p=1.000 n=12}
_Types	_2,846,836	_2,846,836	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,583,097k (± 0.01%)}	_{5,582,840k (± 0.02%)}	_~	_5,581,341k	_5,588,413k	_{p=0.219 n=12}
_{Memory Allocs}	_{43,023,299 (± 0.04%)}	_{43,014,412 (± 0.02%)}	_~	_43,004,109	_43,060,263	_{p=0.242 n=12}
_{Config Time}	_{0.063s (± 0.29%)}	_{0.063s (± 0.49%)}	_~	_0.063s	_0.064s	_{p=0.317 n=12}
_{Parse Time}	_{1.625s (± 2.94%)}	_{1.628s (± 2.95%)}	_~	_1.534s	_1.746s	_{p=0.887 n=12}
_{Bind Time}	_{0.414s (±18.56%)}	_{0.426s (±16.26%)}	_~	_0.348s	_0.701s	_{p=0.415 n=12}
_{Check Time}	_{10.103s (± 1.55%)}	_{10.059s (± 1.66%)}	_~	_9.688s	_10.310s	_{p=0.920 n=12}
_{Emit Time}	_{3.546s (±12.25%)}	_{3.736s (±12.79%)}	_~	_3.094s	_4.715s	_{p=0.326 n=12}
_{Total Time}	_{15.844s (± 2.02%)}	_{16.009s (± 2.13%)}	_~	_15.483s	_16.838s	_{p=0.291 n=12}
_{webpack - native}
_Errors	₅₄₄	₅₄₄	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_850,538	_850,538	_~	_~	_~	_{p=1.000 n=12}
_Types	_386,910	_386,910	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{653,045k (± 0.01%)}	_{652,975k (± 0.03%)}	_~	_652,185k	_653,275k	_{p=0.713 n=12}
_{Memory Allocs}	_{4,344,434 (± 0.06%)}	_{4,342,582 (± 0.02%)}	_~	_4,341,158	_4,346,905	_{p=0.514 n=12}
_{Config Time}	_0.008s	_{0.008s (± 4.45%)}	_~	_0.008s	_0.010s	_{p=1.000 n=12}
_{Parse Time}	_{0.211s (± 2.29%)}	_{0.219s (± 2.00%)}	_{+0.007s (+ 3.47%)}	_0.205s	_0.231s	_{p=0.029 n=12}
_{Bind Time}	_{0.047s (±13.13%)}	_{0.048s (±16.42%)}	_~	_0.041s	_0.079s	_{p=0.874 n=12}
_{Check Time}	_{1.271s (± 1.10%)}	_{1.277s (± 1.42%)}	_~	_1.227s	_1.355s	_{p=0.755 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.562s (± 0.53%)}	_{1.575s (± 1.04%)}	_~	_1.547s	_1.653s	_{p=0.090 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,022,532	_1,022,532	_~	_~	_~	_{p=1.000 n=12}
_Types	_376,962	_376,962	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{603,507k (± 0.01%)}	_{603,509k (± 0.01%)}	_~	_603,346k	_603,622k	_{p=0.932 n=12}
_{Memory Allocs}	_{4,754,030 (± 0.03%)}	_{4,754,022 (± 0.03%)}	_~	_4,749,215	_4,758,918	_{p=0.887 n=12}
_{Config Time}	_{0.003s (±12.54%)}	_{0.003s (± 8.64%)}	_~	_0.002s	_0.003s	_{p=0.371 n=12}
_{Parse Time}	_{0.147s (± 3.39%)}	_{0.144s (± 2.59%)}	_~	_0.135s	_0.152s	_{p=0.354 n=12}
_{Bind Time}	_{0.044s (±20.71%)}	_{0.043s (±16.52%)}	_~	_0.033s	_0.065s	_{p=0.944 n=12}
_{Check Time}	_{1.039s (± 0.84%)}	_{1.037s (± 0.56%)}	_~	_1.022s	_1.054s	_{p=0.788 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.242s (± 0.98%)}	_{1.238s (± 0.92%)}	_~	_1.216s	_1.268s	_{p=0.681 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
strada-build-src - native
strada-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

Download Benchmarks

typescript-automation · 2026-09-02T18:28:46Z

Jake Bailey (@jakebailey) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/64131/merge:

Everything looks good!

Fixed anyFunctionType leak

d3f3b5b

Copilot AI balanced review requested due to automatic review settings September 2, 2026 09:49

github-project-automation Bot added this to PR Backlog Sep 2, 2026

github-project-automation Bot moved this to Not started in PR Backlog Sep 2, 2026

typescript-automation Bot added For Backlog Bug PRs that fix a backlog bug labels Sep 2, 2026

Copilot started reviewing on behalf of Mateusz Burzyński (Andarist) September 2, 2026 09:50 View session

Copilot AI reviewed Sep 2, 2026

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Comment thread tsc/testdata/tests/cases/compiler/contextualTypingGenericFunction2.ts Outdated

Correct contextual typing test coverage

7f4cfef

Jake Bailey (jakebailey) approved these changes Sep 2, 2026

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github-project-automation Bot moved this from Not started to Needs merge in PR Backlog Sep 2, 2026

Jake Bailey (jakebailey) added this pull request to the merge queue Sep 2, 2026

Merged via the queue into microsoft:main with commit cf7b936 Sep 2, 2026
26 checks passed

github-project-automation Bot moved this from Needs merge to Done in PR Backlog Sep 2, 2026

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Fixed `anyFunctionType` leak - #64131

Fixed `anyFunctionType` leak#64131
Jake Bailey (jakebailey) merged 2 commits into
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