Fix crash on private constructors in intersection base types by Andarist · Pull Request #64165 · microsoft/TypeScript

Mateusz Burzyński (Andarist) · 2026-09-04T07:29:53Z

Copilot

🟢 Approval recommended

The focused checker change safely handles all constructor signatures and includes comprehensive regression baselines.

Pull request overview

Prevents crashes when intersection base types include private constructors by checking each constructor’s declaring class.

Changes:

Centralizes constructor accessibility checks across extension and instantiation paths.
Adds regression and edge-case coverage with diagnostic, type, and symbol baselines.

File summaries

File	Description
`tsc/internal/checker/checker.go`	Safely resolves inaccessible constructors.
`tsc/testdata/tests/cases/compiler/extendPrivateConstructorClass2.ts`	Adds compiler regression cases.
`tsc/testdata/baselines/reference/compiler/extendPrivateConstructorClass2.errors.txt`	Records expected diagnostics.
`tsc/testdata/baselines/reference/compiler/extendPrivateConstructorClass2.types`	Records inferred types.
`tsc/testdata/baselines/reference/compiler/extendPrivateConstructorClass2.symbols`	Records symbol resolution.

Review details

Files reviewed: 5/5 changed files
Comments generated: 0
Review effort level: Balanced

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Jake Bailey (jakebailey) · 2026-09-04T18:30:58Z

TypeScript Bot (@typescript-bot) test it

typescript-automation · 2026-09-04T18:31:03Z

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 · 2026-09-04T18:53:28Z

Jake Bailey (@jakebailey) Here are the results of running the user tests with tsc comparing main and refs/pull/64165/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 · 2026-09-04T18:58:56Z

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}	_{148,626k (± 0.50%)}	_{148,728k (± 0.56%)}	_~	_146,974k	_150,750k	_{p=0.977 n=12}
_{Memory Allocs}	_{2,271,376 (± 0.00%)}	_{2,271,275 (± 0.00%)}	_{-101 (- 0.00%)}	_2,271,068	_2,271,422	_{p=0.039 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.041s (± 2.59%)}	_{0.041s (± 2.44%)}	_~	_0.039s	_0.044s	_{p=0.839 n=12}
_{Bind Time}	_{0.011s (± 9.56%)}	_{0.013s (±11.85%)}	_~	_0.010s	_0.017s	_{p=0.102 n=12}
_{Check Time}	_{0.495s (± 0.74%)}	_{0.486s (± 0.58%)}	_{-0.008s (- 1.68%)}	_0.481s	_0.495s	_{p=0.000 n=12}
_{Emit Time}	_{0.271s (± 1.67%)}	_{0.267s (± 1.55%)}	_~	_0.257s	_0.277s	_{p=0.450 n=12}
_{Total Time}	_{0.824s (± 0.65%)}	_{0.814s (± 0.68%)}	_{-0.010s (- 1.25%)}	_0.800s	_0.827s	_{p=0.010 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{847,507 (± 0.10%)}	_{847,074 (± 0.08%)}	_~	_844,221	_848,116	_{p=0.347 n=12}
_Types	_{249,851 (± 0.00%)}	_{249,851 (± 0.00%)}	_~	_249,849	_249,855	_{p=0.868 n=12}
_{Memory Used}	_{793,285k (± 0.06%)}	_{792,961k (± 0.03%)}	_~	_792,279k	_793,820k	_{p=0.198 n=12}
_{Memory Allocs}	_{12,963,268 (± 0.07%)}	_{12,963,518 (± 0.13%)}	_~	_12,948,196	_13,022,160	_{p=0.478 n=12}
_{Config Time}	_0.016s	_0.016s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.274s (± 2.47%)}	_{0.273s (± 2.13%)}	_~	_0.260s	_0.286s	_{p=0.723 n=12}
_{Bind Time}	_{0.064s (±15.77%)}	_{0.060s (± 4.82%)}	_~	_0.056s	_0.073s	_{p=0.844 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.634s (± 0.86%)}	_{1.623s (± 0.54%)}	_~	_1.606s	_1.661s	_{p=0.110 n=12}
_{Total Time}	_{2.004s (± 1.03%)}	_{1.987s (± 0.80%)}	_{-0.016s (- 0.80%)}	_1.964s	_2.063s	_{p=0.015 n=12}
_{mui-docs - native}
_Errors	_{11,276 (± 0.05%)}	_{11,276 (± 0.03%)}	_~	_11,263	_11,280	_{p=0.287 n=12}
_Symbols	_4,530,236	_4,530,236	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,524,292	_1,524,292	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,376,413k (± 0.04%)}	_{5,375,487k (± 0.02%)}	_~	_5,372,750k	_5,378,100k	_{p=0.514 n=12}
_{Memory Allocs}	_{46,346,142 (± 0.06%)}	_{46,333,297 (± 0.03%)}	_~	_46,277,860	_46,360,685	_{p=0.514 n=12}
_{Config Time}	_{0.016s (± 1.81%)}	_{0.016s (± 1.98%)}	_~	_0.015s	_0.016s	_{p=1.000 n=12}
_{Parse Time}	_{0.556s (± 1.28%)}	_{0.558s (± 1.36%)}	_~	_0.534s	_0.574s	_{p=0.966 n=12}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{16.119s (± 0.35%)}	_{16.014s (± 0.41%)}	_{-0.104s (- 0.65%)}	_15.898s	_16.172s	_{p=0.004 n=12}
_{Emit Time}	_{0.431s (± 0.25%)}	_{0.433s (± 0.30%)}	_{+0.002s (+ 0.39%)}	_0.431s	_0.436s	_{p=0.045 n=12}
_{Total Time}	_{17.911s (± 0.66%)}	_{17.747s (± 0.52%)}	_{-0.163s (- 0.91%)}	_17.598s	_17.965s	_{p=0.004 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}	_{1,643,131k (± 0.20%)}	_{1,648,849k (± 0.26%)}	_~	_1,639,158k	_1,661,137k	_{p=0.068 n=12}
_{Memory Allocs}	_{97,017,287 (± 0.03%)}	_{97,070,265 (± 0.05%)}	_~	_96,955,799	_97,159,967	_{p=0.078 n=12}
_{Config Time}	_{0.004s (±13.98%)}	_{0.004s (±11.15%)}	_~	_0.003s	_0.006s	_{p=0.846 n=12}
_{Parse Time}	_{0.197s (± 3.20%)}	_{0.195s (± 2.60%)}	_~	_0.182s	_0.207s	_{p=0.560 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.812s (± 0.48%)}	_{1.803s (± 0.33%)}	_{-0.009s (- 0.49%)}	_1.781s	_1.816s	_{p=0.044 n=12}
_{Emit Time}	_{0.277s (± 5.39%)}	_{0.271s (± 5.54%)}	_~	_0.241s	_0.319s	_{p=0.369 n=12}
_{Total Time}	_{24.850s (± 0.74%)}	_{24.659s (± 0.67%)}	_~	_24.119s	_24.997s	_{p=0.160 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}	_{319,626k (± 0.07%)}	_{319,558k (± 0.08%)}	_~	_319,085k	_320,749k	_{p=0.671 n=12}
_{Memory Allocs}	_{4,673,031 (± 0.01%)}	_{4,672,871 (± 0.01%)}	_~	_4,671,427	_4,673,658	_{p=0.630 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.113s (± 3.68%)}	_{0.116s (± 5.25%)}	_~	_0.102s	_0.131s	_{p=0.468 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.053s (± 0.46%)}	_{1.043s (± 0.57%)}	_{-0.011s (- 1.01%)}	_1.026s	_1.056s	_{p=0.010 n=12}
_{Emit Time}	_{0.128s (±11.78%)}	_{0.144s (± 9.69%)}	_~	_0.103s	_0.172s	_{p=0.110 n=12}
_{Total Time}	_{1.349s (± 0.67%)}	_{1.355s (± 0.89%)}	_~	_1.329s	_1.402s	_{p=0.370 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}	_{277,186k (± 0.03%)}	_{277,180k (± 0.02%)}	_~	_277,024k	_277,344k	_{p=0.977 n=12}
_{Memory Allocs}	_{1,641,752 (± 0.01%)}	_{1,641,877 (± 0.01%)}	_~	_1,641,488	_1,642,593	_{p=0.378 n=12}
_{Config Time}	_{0.000s (±146.91%)}	_{0.000s (±146.91%)}	_~	_0.000s	_0.001s	_{p=1.000 n=12}
_{Parse Time}	_{0.097s (± 4.06%)}	_{0.100s (± 3.83%)}	_~	_0.089s	_0.112s	_{p=0.084 n=12}
_{Bind Time}	_{0.039s (±10.34%)}	_{0.037s (±10.09%)}	_~	_0.028s	_0.049s	_{p=0.339 n=12}
_{Check Time}	_{0.834s (± 0.62%)}	_{0.832s (± 0.54%)}	_~	_0.823s	_0.849s	_{p=0.639 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.984s (± 0.81%)}	_{0.983s (± 0.67%)}	_~	_0.969s	_1.005s	_{p=0.854 n=12}
_{vscode - native}
_Errors	₃₄₉	₃₄₉	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_8,306,979	_8,306,979	_~	_~	_~	_{p=1.000 n=12}
_Types	_2,849,181	_2,849,181	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,622,155k (± 0.01%)}	_{5,622,322k (± 0.02%)}	_~	_5,620,524k	_5,625,473k	_{p=1.000 n=12}
_{Memory Allocs}	_{43,213,350 (± 0.03%)}	_{43,210,400 (± 0.01%)}	_~	_43,199,664	_43,233,957	_{p=0.843 n=12}
_{Config Time}	_{0.063s (± 0.39%)}	_{0.064s (± 0.51%)}	_~	_0.063s	_0.064s	_{p=0.089 n=12}
_{Parse Time}	_{1.640s (± 2.71%)}	_{1.655s (± 3.10%)}	_~	_1.516s	_1.761s	_{p=0.723 n=12}
_{Bind Time}	_{0.423s (±14.03%)}	_{0.432s (±19.83%)}	_~	_0.351s	_0.714s	_{p=0.875 n=12}
_{Check Time}	_{10.149s (± 1.51%)}	_{10.198s (± 1.54%)}	_~	_9.796s	_10.393s	_{p=0.319 n=12}
_{Emit Time}	_{3.860s (±12.93%)}	_{3.725s (±13.03%)}	_~	_3.160s	_4.953s	_{p=0.887 n=12}
_{Total Time}	_{16.234s (± 2.28%)}	_{16.169s (± 2.29%)}	_~	_15.723s	_17.196s	_{p=0.876 n=12}
_{webpack - native}
_Errors	₅₄₅	₅₄₅	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_918,784	_918,784	_~	_~	_~	_{p=1.000 n=12}
_Types	_421,470	_421,470	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{705,499k (± 0.02%)}	_{705,334k (± 0.03%)}	_~	_704,864k	_705,704k	_{p=0.242 n=12}
_{Memory Allocs}	_{4,582,518 (± 0.04%)}	_{4,581,819 (± 0.02%)}	_~	_4,579,692	_4,585,047	_{p=0.551 n=12}
_{Config Time}	_0.008s	_{0.008s (± 5.88%)}	_~	_0.008s	_0.010s	_{p=0.478 n=12}
_{Parse Time}	_{0.222s (± 1.93%)}	_{0.222s (± 2.28%)}	_~	_0.210s	_0.237s	_{p=0.468 n=12}
_{Bind Time}	_{0.046s (± 8.10%)}	_{0.051s (±14.71%)}	_~	_0.042s	_0.078s	_{p=0.535 n=12}
_{Check Time}	_{1.284s (± 0.80%)}	_{1.286s (± 1.24%)}	_~	_1.248s	_1.346s	_{p=0.876 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.584s (± 0.67%)}	_{1.593s (± 1.43%)}	_~	_1.563s	_1.684s	_{p=0.702 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}	_{603,554k (± 0.01%)}	_{603,452k (± 0.01%)}	_{-102k (- 0.02%)}	_603,255k	_603,611k	_{p=0.033 n=12}
_{Memory Allocs}	_{4,755,467 (± 0.03%)}	_{4,755,843 (± 0.03%)}	_~	_4,751,691	_4,759,577	_{p=0.755 n=12}
_{Config Time}	_{0.003s (± 8.64%)}	_{0.003s (±11.61%)}	_~	_0.002s	_0.003s	_{p=0.640 n=12}
_{Parse Time}	_{0.144s (± 3.67%)}	_{0.154s (± 2.26%)}	_{🔻+0.010s (+ 6.64%)}	_0.143s	_0.163s	_{p=0.005 n=12}
_{Bind Time}	_{0.050s (±16.26%)}	_{0.039s (±10.39%)}	_{🟩-0.011s (-22.24%)}	_0.033s	_0.053s	_{p=0.026 n=12}
_{Check Time}	_{1.036s (± 0.59%)}	_{1.045s (± 1.11%)}	_~	_1.022s	_1.084s	_{p=0.213 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.245s (± 0.91%)}	_{1.251s (± 1.20%)}	_~	_1.224s	_1.295s	_{p=0.600 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 · 2026-09-04T19:31:52Z

Jake Bailey (@jakebailey) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/64165/merge:

Everything looks good!

Fix crash on private constructors in intersection base types

7bedb5e

Copilot AI balanced review requested due to automatic review settings September 4, 2026 07:29

github-project-automation Bot added this to PR Backlog Sep 4, 2026

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typescript-automation Bot added For Backlog Bug PRs that fix a backlog bug labels Sep 4, 2026

Copilot started reviewing on behalf of Mateusz Burzyński (Andarist) September 4, 2026 07:30 View session

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github-project-automation Bot moved this from Not started to Needs merge in PR Backlog Sep 4, 2026

Jake Bailey (jakebailey) added this pull request to the merge queue Sep 4, 2026

Merged via the queue into microsoft:main with commit ab6a5a0 Sep 4, 2026
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github-project-automation Bot moved this from Needs merge to Done in PR Backlog Sep 4, 2026

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Fix crash on private constructors in intersection base types - #64165

Fix crash on private constructors in intersection base types#64165
Jake Bailey (jakebailey) merged 1 commit into
microsoft:mainfrom
Andarist:fix/private-intersection-constructor-accessibility

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