Restore idempotency to `resolveObjectTypeMembers` by ahejlsberg · Pull Request #64372 · microsoft/TypeScript

Anders Hejlsberg (ahejlsberg) · 2026-09-21T15:32:03Z

With this PR we restore idempotent behavior to resolveObjectTypeMembers as was originally intended. In #20400 we allowed type arguments to base types of a class or interface to observe the partially resolved set of members of that class or interface. This ends up being a source of ghost errors as for example observed in #62180. We really shouldn't do this and I think it is perfectly acceptable to disallow base class type arguments from eagerly obtaining the resolved set of members of the class or interface being declared.

Fixes #62180.

Anders Hejlsberg (ahejlsberg) · 2026-09-21T15:33:24Z

TypeScript Bot (@typescript-bot) test it

typescript-automation · 2026-09-21T15:33:31Z

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

Command	Status	Results
`test top400`	✅ Started
`user test this`	✅ Started
`run dt`	❌ Error: `Error: TF215106: Access denied. typescriptbot-github3 needs Queue builds permissions for build pipeline 79:TypeScript PR DT Tests in team project TypeScript to perform the action. For more information, contact the Azure DevOps administrator.`
`perf test this faster`	✅ Started	👀 Results

Copilot

Copilot review overview

🟡 Changes recommended

Renumbering FromTypeNode breaks the exported ObjectFlags contract and generated enum synchronization.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 1

Open (1)

Preserve removed bit to avoid FromTypeNode enum serialization breakage · New

What changed in this PR

Restores idempotent object-member resolution and prevents partially resolved members from causing ghost diagnostics.

Changes:

Delays publishing structured members until resolution completes.
Removes unresolved-member cache state.
Adds regression coverage and updates affected baselines.

File	Description
`tsc/internal/checker/checker.go`	Revises member resolution and caching.
`tsc/internal/checker/types.go`	Removes the unresolved-members flag.
`tsc/internal/fourslash/tests/noGhostErrors_test.go`	Tests recursive inference without ghost errors.
`tsc/testdata/baselines/reference/compiler/recursiveTypeInference.types`	Updates inferred recursive types.
`tsc/testdata/baselines/reference/compiler/mutuallyRecursiveInference.errors.txt`	Records new recursion-depth diagnostic.
`tsc/testdata/baselines/reference/compiler/keyofGenericExtendingClassDoubleLayer.errors.txt`	Records new recursion-depth diagnostic.

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 	ObjectFlagsIdenticalBaseTypeExists     = 1 << 28 // has a defined cachedEquivalentBaseType member
-	ObjectFlagsUnresolvedMembers           = 1 << 29 // Member resolution in process
-	ObjectFlagsFromTypeNode                = 1 << 30 // Originates in resolution of AST type node
+	ObjectFlagsFromTypeNode                = 1 << 29 // Originates in resolution of AST type node


Jake Bailey (jakebailey) · 2026-09-21T15:46:35Z

I fixed the DT error (forgot to grant a perm), but note that DT doesn't check 7.0 or 7.1 quite yet.

typescript-automation · 2026-09-21T15:58:50Z

Anders Hejlsberg (@ahejlsberg)
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	_96,949	_96,949	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{148,450k (± 0.41%)}	_{149,016k (± 0.54%)}	_~	_147,047k	_150,787k	_{p=0.291 n=12}
_{Memory Allocs}	_{2,271,609 (± 0.01%)}	_{2,269,434 (± 0.00%)}	_{-2,175 (- 0.10%)}	_2,269,214	_2,269,755	_{p=0.000 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.041s (± 4.59%)}	_{0.042s (± 3.64%)}	_~	_0.039s	_0.047s	_{p=0.256 n=12}
_{Bind Time}	_{0.013s (±10.83%)}	_{0.012s (±12.82%)}	_~	_0.010s	_0.018s	_{p=0.254 n=12}
_{Check Time}	_{0.503s (± 0.70%)}	_{0.509s (± 0.78%)}	_{+0.007s (+ 1.31%)}	_0.502s	_0.521s	_{p=0.011 n=12}
_{Emit Time}	_{0.273s (± 2.17%)}	_{0.270s (± 2.05%)}	_~	_0.253s	_0.283s	_{p=0.944 n=12}
_{Total Time}	_{0.836s (± 0.66%)}	_{0.840s (± 0.69%)}	_~	_0.829s	_0.860s	_{p=0.172 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{847,386 (± 0.10%)}	_{846,885 (± 0.06%)}	_~	_845,477	_848,037	_{p=0.068 n=12}
_Types	_{250,003 (± 0.00%)}	_{250,003 (± 0.00%)}	_~	_250,001	_250,013	_{p=0.755 n=12}
_{Memory Used}	_{793,676k (± 0.05%)}	_{793,498k (± 0.06%)}	_~	_792,122k	_795,266k	_{p=0.478 n=12}
_{Memory Allocs}	_{12,958,810 (± 0.03%)}	_{12,944,638 (± 0.02%)}	_{-14,172 (- 0.11%)}	_12,941,340	_12,957,586	_{p=0.000 n=12}
_{Config Time}	_{0.016s (± 1.13%)}	_0.016s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.270s (± 3.14%)}	_{0.273s (± 2.13%)}	_~	_0.255s	_0.291s	_{p=0.434 n=12}
_{Bind Time}	_{0.067s (±15.78%)}	_{0.062s (± 6.49%)}	_~	_0.059s	_0.078s	_{p=0.856 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.636s (± 1.59%)}	_{1.617s (± 1.48%)}	_~	_1.574s	_1.693s	_{p=0.182 n=12}
_{Total Time}	_{2.009s (± 1.61%)}	_{1.985s (± 1.33%)}	_~	_1.944s	_2.067s	_{p=0.117 n=12}
_{mui-docs - native}
_Errors	_{11,348 (± 0.02%)}	_{11,347 (± 0.01%)}	_~	_11,344	_11,349	_{p=0.054 n=12}
_Symbols	_4,305,148	_4,305,148	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,451,831	_1,451,831	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{4,154,537k (± 0.06%)}	_{4,155,107k (± 0.04%)}	_~	_4,150,997k	_4,158,698k	_{p=0.755 n=12}
_{Memory Allocs}	_{39,225,804 (± 0.05%)}	_{39,169,392 (± 0.03%)}	_{-56,413 (- 0.14%)}	_39,127,355	_39,193,834	_{p=0.000 n=12}
_{Config Time}	_{0.016s (± 1.81%)}	_{0.016s (± 1.98%)}	_~	_0.015s	_0.016s	_{p=1.000 n=12}
_{Parse Time}	_{0.566s (± 1.50%)}	_{0.559s (± 3.35%)}	_~	_0.482s	_0.596s	_{p=1.000 n=12}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{15.059s (± 0.15%)}	_{15.024s (± 0.23%)}	_~	_14.922s	_15.096s	_{p=0.103 n=12}
_{Emit Time}	_{0.474s (±11.46%)}	_{0.438s (± 2.77%)}	_~	_0.425s	_0.472s	_{p=0.231 n=12}
_{Total Time}	_{16.882s (± 0.42%)}	_{16.782s (± 0.34%)}	_{-0.100s (- 0.59%)}	_16.635s	_16.991s	_{p=0.007 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	_443,566	_443,566	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,643,473k (± 0.31%)}	_{1,645,781k (± 0.23%)}	_~	_1,632,510k	_1,653,633k	_{p=0.410 n=12}
_{Memory Allocs}	_{96,964,620 (± 0.04%)}	_{96,933,860 (± 0.04%)}	_~	_96,818,842	_97,019,427	_{p=0.160 n=12}
_{Config Time}	_{0.004s (±11.61%)}	_{0.004s (± 9.48%)}	_~	_0.003s	_0.005s	_{p=1.000 n=12}
_{Parse Time}	_{0.190s (± 3.15%)}	_{0.197s (± 2.34%)}	_{+0.007s (+ 3.78%)}	_0.186s	_0.208s	_{p=0.050 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.856s (± 0.29%)}	_{1.856s (± 0.32%)}	_~	_1.844s	_1.874s	_{p=1.000 n=12}
_{Emit Time}	_{0.268s (± 6.29%)}	_{0.279s (± 4.34%)}	_~	_0.233s	_0.301s	_{p=0.370 n=12}
_{Total Time}	_{24.960s (± 0.86%)}	_{25.158s (± 0.80%)}	_~	_24.503s	_25.659s	_{p=0.203 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_337,531	_337,531	_~	_~	_~	_{p=1.000 n=12}
_Types	_198,885	_198,885	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{319,701k (± 0.07%)}	_{319,566k (± 0.04%)}	_~	_319,274k	_320,087k	_{p=0.291 n=12}
_{Memory Allocs}	_{4,673,007 (± 0.01%)}	_{4,668,940 (± 0.01%)}	_{-4,066 (- 0.09%)}	_4,667,369	_4,670,214	_{p=0.000 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.112s (± 4.82%)}	_{0.111s (± 4.23%)}	_~	_0.098s	_0.123s	_{p=0.877 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.080s (± 0.55%)}	_{1.086s (± 0.49%)}	_~	_1.070s	_1.098s	_{p=0.085 n=12}
_{Emit Time}	_{0.131s (±13.09%)}	_{0.120s (±12.83%)}	_~	_0.093s	_0.159s	_{p=0.401 n=12}
_{Total Time}	_{1.377s (± 1.14%)}	_{1.373s (± 0.94%)}	_~	_1.345s	_1.412s	_{p=0.619 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	_181,926	_181,926	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{277,193k (± 0.03%)}	_{277,127k (± 0.01%)}	_~	_277,029k	_277,267k	_{p=0.193 n=12}
_{Memory Allocs}	_{1,642,050 (± 0.01%)}	_{1,634,541 (± 0.01%)}	_{-7,509 (- 0.46%)}	_1,634,146	_1,634,968	_{p=0.000 n=12}
_{Config Time}	_{0.000s (±217.90%)}	_{0.000s (±217.90%)}	_~	_0.000s	_0.001s	_{p=1.000 n=12}
_{Parse Time}	_{0.099s (± 4.79%)}	_{0.100s (± 3.48%)}	_~	_0.090s	_0.108s	_{p=0.702 n=12}
_{Bind Time}	_{0.036s (±12.47%)}	_{0.039s (±13.84%)}	_~	_0.028s	_0.053s	_{p=0.123 n=12}
_{Check Time}	_{0.848s (± 0.62%)}	_{0.843s (± 0.57%)}	_~	_0.829s	_0.853s	_{p=0.173 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.997s (± 0.94%)}	_{0.996s (± 0.94%)}	_~	_0.974s	_1.017s	_{p=0.744 n=12}
_{vscode - native}
_Errors	₃₈₆	₃₈₆	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_9,235,564	_9,235,564	_~	_~	_~	_{p=1.000 n=12}
_Types	_3,154,404	_3,154,404	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{6,165,406k (± 0.02%)}	_{6,165,657k (± 0.02%)}	_~	_6,163,161k	_6,169,642k	_{p=0.671 n=12}
_{Memory Allocs}	_{47,091,555 (± 0.03%)}	_{46,971,469 (± 0.03%)}	_{-120,086 (- 0.26%)}	_46,952,929	_47,016,004	_{p=0.000 n=12}
_{Config Time}	_{0.065s (± 0.28%)}	_{0.065s (± 0.28%)}	_~	_0.064s	_0.065s	_{p=1.000 n=12}
_{Parse Time}	_{1.727s (± 3.01%)}	_{1.712s (± 3.59%)}	_~	_1.597s	_1.871s	_{p=0.630 n=12}
_{Bind Time}	_{0.507s (±20.53%)}	_{0.527s (±21.58%)}	_~	_0.378s	_0.791s	_{p=0.560 n=12}
_{Check Time}	_{11.143s (± 1.33%)}	_{11.134s (± 1.62%)}	_~	_10.780s	_11.455s	_{p=0.787 n=12}
_{Emit Time}	_{4.437s (±11.89%)}	_{4.266s (±12.88%)}	_~	_3.457s	_5.344s	_{p=0.369 n=12}
_{Total Time}	_{17.985s (± 2.43%)}	_{17.815s (± 2.53%)}	_~	_17.059s	_18.699s	_{p=0.219 n=12}
_{webpack - native}
_Errors	₈₄₂	₈₄₃	_{+1 (+ 0.12%)}	_~	_~	_{p=0.000 n=12}
_Symbols	_1,397,420	_1,397,446	_{+26 (+ 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_605,320	_605,325	_{+5 (+ 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{968,564k (± 0.01%)}	_{968,473k (± 0.02%)}	_~	_967,926k	_969,090k	_{p=0.551 n=12}
_{Memory Allocs}	_{6,247,584 (± 0.02%)}	_{6,218,984 (± 0.02%)}	_{-28,600 (- 0.46%)}	_6,216,067	_6,224,018	_{p=0.000 n=12}
_{Config Time}	_{0.009s (± 2.77%)}	_{0.009s (± 5.25%)}	_~	_0.009s	_0.011s	_{p=0.137 n=12}
_{Parse Time}	_{0.253s (± 2.94%)}	_{0.269s (± 3.39%)}	_{🔻+0.015s (+ 6.05%)}	_0.247s	_0.300s	_{p=0.010 n=12}
_{Bind Time}	_{0.068s (±19.30%)}	_{0.073s (±16.61%)}	_~	_0.054s	_0.105s	_{p=0.235 n=12}
_{Check Time}	_{1.871s (± 0.40%)}	_{1.911s (± 1.82%)}	_~	_1.861s	_2.010s	_{p=0.075 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{2.237s (± 0.34%)}	_{2.302s (± 1.59%)}	_{+0.065s (+ 2.91%)}	_2.227s	_2.424s	_{p=0.000 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,045,695	_1,045,695	_~	_~	_~	_{p=1.000 n=12}
_Types	_383,049	_383,049	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{611,332k (± 0.01%)}	_{611,319k (± 0.01%)}	_~	_611,114k	_611,563k	_{p=0.990 n=12}
_{Memory Allocs}	_{4,829,565 (± 0.04%)}	_{4,813,490 (± 0.02%)}	_{-16,075 (- 0.33%)}	_4,810,268	_4,816,269	_{p=0.000 n=12}
_{Config Time}	_{0.003s (±11.61%)}	_{0.003s (±12.54%)}	_~	_0.002s	_0.003s	_{p=1.000 n=12}
_{Parse Time}	_{0.150s (± 2.41%)}	_{0.148s (± 4.48%)}	_~	_0.135s	_0.164s	_{p=0.451 n=12}
_{Bind Time}	_{0.038s (±16.55%)}	_{0.047s (±18.09%)}	_{🔻+0.008s (+22.17%)}	_0.034s	_0.070s	_{p=0.019 n=12}
_{Check Time}	_{1.187s (± 0.63%)}	_{1.195s (± 0.85%)}	_~	_1.172s	_1.223s	_{p=0.155 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.388s (± 0.59%)}	_{1.405s (± 0.78%)}	_{+0.017s (+ 1.23%)}	_1.384s	_1.443s	_{p=0.025 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

Anders Hejlsberg (ahejlsberg) · 2026-09-21T18:08:49Z

TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) test top400

typescript-automation · 2026-09-21T18:08:54Z

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

Command	Status	Results
`user test this`	✅ Started	✅ Results
`test top400`	✅ Started	👀 Results

Anders Hejlsberg (ahejlsberg) · 2026-09-21T18:11:13Z

Trying tests again...

typescript-automation · 2026-09-21T18:38:13Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the user tests with tsc comparing main and refs/pull/64372/merge:

There were infrastructure failures potentially unrelated to your change:

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

Otherwise...

Everything looks good!

typescript-automation · 2026-09-21T19:13:47Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/64372/merge:

Something interesting changed - please have a look.

Details

stablyai/orca

14 of 24 projects failed to build with the old tsc and were ignored

config/tsconfig.cli.json

error TS2589: Type instantiation is excessively deep and possibly infinite.
- src/shared/plugins/plugin-host-api.ts#L89 in config/tsconfig.cli.json

config/tsconfig.tc.cli.json

error TS2589: Type instantiation is excessively deep and possibly infinite.
- src/shared/plugins/plugin-host-api.ts#L89 in config/tsconfig.tc.cli.json

config/tsconfig.tc.web.json

error TS2589: Type instantiation is excessively deep and possibly infinite.
- src/shared/plugins/plugin-host-api.ts#L89 in config/tsconfig.tc.web.json

Anders Hejlsberg (ahejlsberg) added 6 commits September 18, 2026 15:40

Idempotent resolution of object type members

0e641ff

Accept new baselines

adb6784

Don't use type resolution stack

4b00dfd

Add fourslash test

99f0df7

Accept new baselines

8a33e98

Remove TypeSystemPropertyName member

3b0239a

Copilot AI balanced review requested due to automatic review settings September 21, 2026 15:32

github-project-automation Bot added this to PR Backlog Sep 21, 2026

typescript-automation Bot assigned Anders Hejlsberg (ahejlsberg) Sep 21, 2026

github-project-automation Bot moved this to Not started in PR Backlog Sep 21, 2026

typescript-automation Bot added Author: Team For Milestone Bug PRs that fix a bug with a specific milestone labels Sep 21, 2026

Copilot started reviewing on behalf of Anders Hejlsberg (ahejlsberg) September 21, 2026 15:32 View session

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Formatting

9cb685e

Anders Hejlsberg (ahejlsberg) added 2 commits September 21, 2026 10:57

Generate enums

698e180

Merge branch 'main' into fix-62180

d2cb226

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Restore idempotency to `resolveObjectTypeMembers` - #64372

Restore idempotency to `resolveObjectTypeMembers`#64372
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fix-62180

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