Improve recursion identities and `isDeeplyNestedType` by ahejlsberg · Pull Request #4913 · microsoft/typescript-go

Anders Hejlsberg (ahejlsberg) · 2026-08-18T15:28:45Z

This PR

Improves recursion identities for indexed access types, and
Removes the "excessive stack depth" relation error.

See reasoning here.

Fixes #4807.

Anders Hejlsberg (ahejlsberg) · 2026-08-18T15:30:27Z

TypeScript Bot (@typescript-bot) test it

typescript-automation · 2026-08-18T15:30:32Z

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

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

Copilot

Pull request overview

Improves recursive type relation handling to avoid false stack-depth errors for deeply circular structures.

Changes:

Refines recursion identities for indexed-access and mapped types.
Treats 100-level relation depth as indeterminate rather than erroneous.
Adds regression coverage and updates affected baselines.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
`internal/checker/relater.go`	Updates recursion detection and removes stack-depth diagnostics.
`testdata/tests/cases/compiler/veryDeepRelations.ts`	Adds the circular-array regression case.
`testdata/baselines/reference/compiler/veryDeepRelations.types`	Records expected type output.
`testdata/baselines/reference/compiler/veryDeepRelations.symbols`	Records expected symbol output.
`testdata/baselines/reference/compiler/excessivelyDeepConditionalTypes.errors.txt`	Removes obsolete stack-depth errors.

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typescript-automation · 2026-08-18T15:59:14Z

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	_96,945	_96,945	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{148,938k (± 0.51%)}	_{149,351k (± 0.52%)}	_~	_147,770k	_151,421k	_{p=0.410 n=12}
_{Memory Allocs}	_{2,271,988 (± 0.00%)}	_{2,272,092 (± 0.00%)}	_~	_2,271,839	_2,272,362	_{p=0.128 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.040s (± 2.43%)}	_{0.040s (± 3.94%)}	_~	_0.037s	_0.047s	_{p=0.176 n=12}
_{Bind Time}	_{0.013s (±13.92%)}	_{0.013s (±11.37%)}	_~	_0.010s	_0.017s	_{p=0.611 n=12}
_{Check Time}	_{0.488s (± 0.79%)}	_{0.485s (± 0.77%)}	_~	_0.479s	_0.502s	_{p=0.350 n=12}
_{Emit Time}	_{0.274s (± 1.72%)}	_{0.272s (± 1.61%)}	_~	_0.257s	_0.281s	_{p=0.681 n=12}
_{Total Time}	_{0.822s (± 0.87%)}	_{0.816s (± 0.86%)}	_~	_0.794s	_0.837s	_{p=0.224 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{847,930 (± 0.08%)}	_{847,209 (± 0.08%)}	_~	_845,588	_848,527	_{p=0.160 n=12}
_Types	_{249,912 (± 0.00%)}	_{249,859 (± 0.00%)}	_{-53 (- 0.02%)}	_249,856	_249,868	_{p=0.000 n=12}
_{Memory Used}	_{793,691k (± 0.08%)}	_{792,977k (± 0.05%)}	_{-714k (- 0.09%)}	_792,151k	_794,216k	_{p=0.039 n=12}
_{Memory Allocs}	_{13,037,474 (± 0.03%)}	_{13,036,470 (± 0.02%)}	_~	_13,032,120	_13,045,624	_{p=0.671 n=12}
_{Config Time}	_0.016s	_0.016s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.280s (± 2.66%)}	_{0.283s (± 1.08%)}	_~	_0.274s	_0.290s	_{p=0.385 n=12}
_{Bind Time}	_{0.064s (± 9.40%)}	_{0.059s (± 0.45%)}	_{🟩-0.005s (- 8.17%)}	_0.058s	_0.060s	_{p=0.044 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.642s (± 1.20%)}	_{1.630s (± 0.48%)}	_~	_1.610s	_1.651s	_{p=0.434 n=12}
_{Total Time}	_{2.023s (± 1.25%)}	_{2.002s (± 0.45%)}	_~	_1.980s	_2.028s	_{p=0.091 n=12}
_{mui-docs - native}
_Errors	_{11,279 (± 0.01%)}	_{11,279 (± 0.01%)}	_~	_11,272	_11,281	_{p=0.732 n=12}
_Symbols	_4,602,406	_4,592,664	_{-9,742 (- 0.21%)}	_~	_~	_{p=0.000 n=12}
_Types	_1,639,118	_1,636,666	_{-2,452 (- 0.15%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{5,614,828k (± 0.04%)}	_{5,567,394k (± 0.03%)}	_{-47,434k (- 0.84%)}	_5,565,259k	_5,573,494k	_{p=0.000 n=12}
_{Memory Allocs}	_{53,523,823 (± 0.04%)}	_{53,332,087 (± 0.04%)}	_{-191,736 (- 0.36%)}	_53,279,229	_53,408,996	_{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}	_{0.556s (± 2.05%)}	_{0.550s (± 2.07%)}	_~	_0.511s	_0.578s	_{p=0.504 n=12}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{17.222s (± 0.37%)}	_{17.164s (± 0.38%)}	_~	_16.937s	_17.260s	_{p=0.110 n=12}
_{Emit Time}	_{0.451s (± 2.68%)}	_{0.479s (±15.64%)}	_~	_0.436s	_0.854s	_{p=0.880 n=12}
_{Total Time}	_{18.995s (± 0.40%)}	_{18.970s (± 0.24%)}	_~	_18.815s	_19.034s	_{p=0.319 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,394,411	_1,394,339	_{-72 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_Types	_443,627	_443,465	_{-162 (- 0.04%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{1,652,649k (± 0.34%)}	_{1,650,123k (± 0.28%)}	_~	_1,636,930k	_1,661,651k	_{p=0.347 n=12}
_{Memory Allocs}	_{97,232,180 (± 0.05%)}	_{97,230,805 (± 0.04%)}	_~	_97,131,442	_97,347,114	_{p=0.977 n=12}
_{Config Time}	_{0.004s (±12.64%)}	_{0.003s (±16.58%)}	_~	_0.002s	_0.005s	_{p=0.337 n=12}
_{Parse Time}	_{0.196s (± 2.88%)}	_{0.200s (± 2.68%)}	_~	_0.187s	_0.215s	_{p=0.385 n=12}
_{Bind Time}	_{0.000s (±217.90%)}	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.780s (± 0.49%)}	_{1.777s (± 0.29%)}	_~	_1.761s	_1.787s	_{p=0.966 n=12}
_{Emit Time}	_{0.287s (± 5.49%)}	_{0.295s (± 2.66%)}	_~	_0.275s	_0.312s	_{p=0.417 n=12}
_{Total Time}	_{24.574s (± 0.84%)}	_{24.650s (± 0.53%)}	_~	_24.338s	_24.955s	_{p=0.478 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_337,618	_337,586	_{-32 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_Types	_198,941	_198,869	_{-72 (- 0.04%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{319,661k (± 0.03%)}	_{319,508k (± 0.02%)}	_{-154k (- 0.05%)}	_319,322k	_319,626k	_{p=0.010 n=12}
_{Memory Allocs}	_{4,676,796 (± 0.01%)}	_{4,676,666 (± 0.01%)}	_~	_4,676,269	_4,677,512	_{p=0.219 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.115s (± 5.17%)}	_{0.111s (± 5.44%)}	_~	_0.099s	_0.130s	_{p=0.258 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.035s (± 0.47%)}	_{1.032s (± 0.58%)}	_~	_1.015s	_1.046s	_{p=0.504 n=12}
_{Emit Time}	_{0.133s (±13.56%)}	_{0.133s (±12.89%)}	_~	_0.103s	_0.170s	_{p=0.433 n=12}
_{Total Time}	_{1.338s (± 1.23%)}	_{1.332s (± 1.28%)}	_~	_1.292s	_1.376s	_{p=0.724 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_305,341	_305,317	_{-24 (- 0.01%)}	_~	_~	_{p=0.000 n=12}
_Types	_182,038	_181,984	_{-54 (- 0.03%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{277,358k (± 0.02%)}	_{277,271k (± 0.01%)}	_{-88k (- 0.03%)}	_277,154k	_277,357k	_{p=0.034 n=12}
_{Memory Allocs}	_{1,644,624 (± 0.02%)}	_{1,644,200 (± 0.01%)}	_{-424 (- 0.03%)}	_1,643,752	_1,644,724	_{p=0.017 n=12}
_{Config Time}	_{0.000s (±217.90%)}	_{0.000s (±113.79%)}	_~	_0.000s	_0.001s	_{p=0.590 n=12}
_{Parse Time}	_{0.099s (± 3.59%)}	_{0.100s (± 4.60%)}	_~	_0.090s	_0.110s	_{p=0.639 n=12}
_{Bind Time}	_{0.035s (± 9.95%)}	_{0.038s (±13.17%)}	_~	_0.027s	_0.050s	_{p=0.324 n=12}
_{Check Time}	_{0.822s (± 0.51%)}	_{0.820s (± 0.65%)}	_~	_0.802s	_0.834s	_{p=0.434 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.970s (± 0.76%)}	_{0.973s (± 0.80%)}	_~	_0.948s	_0.989s	_{p=0.370 n=12}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_7,866,624	_7,866,592	_{-32 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_2,693,899	_2,693,859	_{-40 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{5,286,397k (± 0.01%)}	_{5,286,853k (± 0.02%)}	_~	_5,284,896k	_5,289,052k	_{p=0.443 n=12}
_{Memory Allocs}	_{40,983,928 (± 0.01%)}	_{40,991,119 (± 0.03%)}	_~	_40,980,752	_41,047,252	_{p=0.178 n=12}
_{Config Time}	_{0.061s (± 0.74%)}	_{0.061s (± 0.59%)}	_~	_0.060s	_0.062s	_{p=0.355 n=12}
_{Parse Time}	_{1.601s (± 1.97%)}	_{1.628s (± 1.47%)}	_~	_1.550s	_1.687s	_{p=0.091 n=12}
_{Bind Time}	_{0.363s (±17.69%)}	_{0.338s (± 1.28%)}	_~	_0.331s	_0.354s	_{p=0.309 n=12}
_{Check Time}	_{9.485s (± 1.27%)}	_{9.496s (± 0.98%)}	_~	_9.110s	_9.580s	_{p=0.921 n=12}
_{Emit Time}	_{3.193s (± 9.85%)}	_{3.147s (± 5.55%)}	_~	_2.985s	_3.937s	_{p=0.899 n=12}
_{Total Time}	_{14.783s (± 1.65%)}	_{14.751s (± 0.64%)}	_~	_14.640s	_15.197s	_{p=0.164 n=12}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,380	_1,380	_~	_~	_~	_{p=1.000 n=12}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{198,774k (± 0.07%)}	_{198,708k (± 0.05%)}	_~	_198,329k	_198,868k	_{p=0.843 n=12}
_{Memory Allocs}	_{841,484 (± 0.14%)}	_{841,678 (± 0.22%)}	_~	_839,659	_847,991	_{p=0.932 n=12}
_{Config Time}	_{0.008s (± 4.74%)}	_{0.008s (± 4.45%)}	_~	_0.008s	_0.010s	_{p=1.000 n=12}
_{Parse Time}	_{0.218s (± 2.73%)}	_{0.217s (± 1.98%)}	_~	_0.202s	_0.227s	_{p=0.522 n=12}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.227s (± 2.77%)}	_{0.226s (± 1.97%)}	_~	_0.210s	_0.237s	_{p=0.486 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,020,005	_1,019,981	_{-24 (- 0.00%)}	_~	_~	_{p=0.000 n=12}
_Types	_376,891	_376,182	_{-709 (- 0.19%)}	_~	_~	_{p=0.000 n=12}
_{Memory Used}	_{603,515k (± 0.02%)}	_{603,286k (± 0.02%)}	_{-229k (- 0.04%)}	_603,033k	_603,541k	_{p=0.003 n=12}
_{Memory Allocs}	_{4,750,574 (± 0.04%)}	_{4,750,125 (± 0.05%)}	_~	_4,743,135	_4,756,476	_{p=0.887 n=12}
_{Config Time}	_0.003s	_0.003s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.146s (± 3.86%)}	_{0.146s (± 3.73%)}	_~	_0.130s	_0.160s	_{p=0.723 n=12}
_{Bind Time}	_{0.045s (±16.11%)}	_{0.045s (±18.31%)}	_~	_0.033s	_0.067s	_{p=0.943 n=12}
_{Check Time}	_{1.022s (± 1.06%)}	_{1.025s (± 1.11%)}	_~	_0.999s	_1.062s	_{p=0.723 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.229s (± 1.20%)}	_{1.230s (± 1.14%)}	_~	_1.199s	_1.258s	_{p=0.966 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 · 2026-08-18T16:53:53Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/4913/merge:

Everything looks good!

…script-go#4913)

Anders Hejlsberg (ahejlsberg) added 4 commits August 18, 2026 07:35

Improve recursion identities and isDeeplyNestedType

b29cfc5

Accept new baselines

0294ee9

Remove "excessive stack depth" relation error

5e2af9b

Add regression test

3f0cf1a

Anders Hejlsberg (ahejlsberg) requested review from Ryan Cavanaugh (RyanCavanaugh) and Jake Bailey (jakebailey) and a balanced review from Copilot August 18, 2026 15:28

Copilot started reviewing on behalf of Anders Hejlsberg (ahejlsberg) August 18, 2026 15:30 View session

Copilot AI reviewed Aug 18, 2026

View reviewed changes

Jake Bailey (jakebailey) approved these changes Aug 18, 2026

View reviewed changes

Anders Hejlsberg (ahejlsberg) added this pull request to the merge queue Aug 18, 2026

Merged via the queue into main with commit 12548e2 Aug 18, 2026
22 checks passed

Anders Hejlsberg (ahejlsberg) deleted the fix-4807 branch August 18, 2026 18:42

Jake Bailey (jakebailey) pushed a commit to jakebailey/TypeScript that referenced this pull request Aug 19, 2026

Improve recursion identities and isDeeplyNestedType (microsoft/type…

ea58062

…script-go#4913)

michijs Bot mentioned this pull request Aug 24, 2026

[master] Michijs Dependabot changes michijs/michijs-template#146

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Improve recursion identities and `isDeeplyNestedType` - #4913

Improve recursion identities and `isDeeplyNestedType`#4913
Anders Hejlsberg (ahejlsberg) merged 4 commits into
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fix-4807

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