Sort by type depth in `inferFromMatchingTypes` function by ahejlsberg · Pull Request #4591 · microsoft/typescript-go

Anders Hejlsberg (ahejlsberg) · 2026-07-10T19:22:08Z

This PR partially reverts #4389 and instead implements a more targeted fix by sorting types by their nesting depth in the inferFromMatchingTypes function.

This fixes the regression in #4462 (but doesn't add a regression test since the repro has multiple dependencies). It also fixes the regression mentioned in oxc-project/tsgolint#1058 and adds that to the tests.

Fixes #4462.

Anders Hejlsberg (ahejlsberg) · 2026-07-10T19:22:30Z

TypeScript Bot (@typescript-bot) perf test this faster

typescript-automation · 2026-07-10T19:22:35Z

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

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

Anders Hejlsberg (ahejlsberg) · 2026-07-10T19:22:50Z

TypeScript Bot (@typescript-bot) test top1000

typescript-automation · 2026-07-10T19:22:54Z

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

Command	Status	Results
`test top1000`	✅ Started	✅ Results

Copilot

Pull request overview

This PR adjusts type inference ordering in the Go checker to prefer inferences derived from more deeply nested generic instantiations, aiming to address regressions introduced after #4389 (notably #4462) while keeping the change targeted. It also updates/accepts compiler baseline outputs and adds coverage for a related downstream regression report.

Changes:

Updates inferFromMatchingTypes to optionally sort matched target types by a computed “type depth” before performing inference.
Removes the prior per-inference-state depth tracking / candidate depth bookkeeping and relies on inference ordering instead.
Adds a regression test for oxc-project/tsgolint#1058 and updates affected baselines (including a submodule conformance baseline change).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
`internal/checker/inference.go`	Implements depth-based sorting of matched targets in `inferFromMatchingTypes` and introduces depth-computation helpers.
`internal/checker/checker.go`	Removes `candidateDepths` from `InferenceInfo` to match the new ordering strategy.
`testdata/tests/cases/compiler/nestedGenericTypeInference.ts`	Adds a compiler regression test for oxc-project/tsgolint#1058.
`testdata/baselines/reference/compiler/nestedGenericTypeInference.types`	Accepts updated `.types` baseline for the new regression test content.
`testdata/baselines/reference/compiler/nestedGenericTypeInference.symbols`	Accepts updated `.symbols` baseline for the new regression test content.
`testdata/baselines/reference/submodule/conformance/assignmentCompatWithGenericCallSignatures2.errors.txt`	Updates the expected error baseline output for this conformance case.
`testdata/baselines/reference/submodule/conformance/assignmentCompatWithGenericCallSignatures2.errors.txt.diff`	Removes the diff baseline, indicating this case no longer differs from the comparison baseline.

 		// First, infer between identically matching source and target constituents and remove the
 		// matching types.
-		tempSources, tempTargets := c.inferFromMatchingTypes(n, sourceTypes, target.Distributed(), (*Checker).isTypeOrBaseIdenticalTo)
+		tempSources, tempTargets := c.inferFromMatchingTypes(n, sourceTypes, target.Types(), (*Checker).isTypeOrBaseIdenticalTo, false /*sort*/)
 		// Next, infer between closely matching source and target constituents and remove
 		// the matching types. Types closely match when they are instantiations of the same
 		// object type or instantiations of the same type alias.
-		sources, targets := c.inferFromMatchingTypes(n, tempSources, tempTargets, (*Checker).isTypeCloselyMatchedBy)
+		sources, targets := c.inferFromMatchingTypes(n, tempSources, tempTargets, (*Checker).isTypeCloselyMatchedBy, true /*sort*/)


Co-authored-by: ahejlsberg <4226954+ahejlsberg@users.noreply.github.com>

typescript-automation · 2026-07-10T19:47:00Z

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	₄	₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{81,823 (± 0.02%)}	_{81,807 (± 0.04%)}	_~	_81,746	_81,834	_{p=0.377 n=6}
_Types	_98,821	_98,821	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{179,889k (± 0.46%)}	_{179,548k (± 0.62%)}	_~	_177,554k	_180,915k	_{p=0.689 n=6}
_{Memory Allocs}	_{2,539,337 (± 0.00%)}	_{2,538,200 (± 0.01%)}	_{-1,138 (- 0.04%)}	_2,537,691	_2,538,404	_{p=0.005 n=6}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.055s (±11.59%)}	_{0.056s (± 9.51%)}	_~	_0.049s	_0.065s	_{p=0.629 n=6}
_{Bind Time}	_{0.021s (±14.37%)}	_{0.014s (±18.36%)}	_{🟩-0.006s (-29.27%)}	_0.012s	_0.019s	_{p=0.012 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.882s (± 0.93%)}	_{0.894s (± 0.91%)}	_{+0.012s (+ 1.34%)}	_0.886s	_0.907s	_{p=0.030 n=6}
_{Total Time}	_{0.959s (± 1.49%)}	_{0.966s (± 0.87%)}	_~	_0.951s	_0.976s	_{p=0.568 n=6}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{872,290 (± 0.12%)}	_{872,427 (± 0.08%)}	_~	_871,575	_873,402	_{p=0.689 n=6}
_Types	_{263,953 (± 0.00%)}	_{263,953 (± 0.00%)}	_~	_263,950	_263,955	_{p=0.794 n=6}
_{Memory Used}	_{829,640k (± 0.05%)}	_{829,309k (± 0.06%)}	_~	_828,792k	_829,965k	_{p=0.173 n=6}
_{Memory Allocs}	_{12,511,949 (± 0.05%)}	_{12,447,186 (± 0.10%)}	_{-64,764 (- 0.52%)}	_12,436,573	_12,470,542	_{p=0.005 n=6}
_{Config Time}	_{0.018s (± 3.13%)}	_{0.018s (± 4.62%)}	_~	_0.017s	_0.019s	_{p=0.859 n=6}
_{Parse Time}	_{0.246s (± 9.55%)}	_{0.257s (± 4.22%)}	_~	_0.244s	_0.276s	_{p=0.575 n=6}
_{Bind Time}	_{0.065s (±38.47%)}	_{0.064s (±30.28%)}	_~	_0.041s	_0.088s	_{p=0.936 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{1.937s (± 1.41%)}	_{1.947s (± 1.83%)}	_~	_1.912s	_1.994s	_{p=0.689 n=6}
_{Total Time}	_{2.276s (± 1.48%)}	_{2.298s (± 0.97%)}	_~	_2.272s	_2.331s	_{p=0.230 n=6}
_{mui-docs - native}
_Errors	_{11,279 (± 0.04%)}	_{11,279 (± 0.01%)}	_~	_11,278	_11,281	_{p=0.217 n=6}
_Symbols	_4,625,557	_4,625,462	_{-95 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_1,618,177	_1,618,161	_{-16 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory Used}	_{5,754,407k (± 0.03%)}	_{5,752,780k (± 0.03%)}	_~	_5,750,053k	_5,755,189k	_{p=0.230 n=6}
_{Memory Allocs}	_{49,729,504 (± 0.04%)}	_{49,659,660 (± 0.06%)}	_{-69,844 (- 0.14%)}	_49,620,043	_49,693,493	_{p=0.005 n=6}
_{Config Time}	_{0.016s (± 3.16%)}	_{0.016s (± 4.99%)}	_~	_0.016s	_0.018s	_{p=0.752 n=6}
_{Parse Time}	_{0.536s (± 1.20%)}	_{0.527s (± 3.57%)}	_~	_0.493s	_0.544s	_{p=0.872 n=6}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{17.151s (± 0.94%)}	_{17.127s (± 1.01%)}	_~	_16.987s	_17.462s	_{p=0.936 n=6}
_{Emit Time}	_{0.518s (±26.89%)}	_{0.465s (± 3.86%)}	_~	_0.453s	_0.501s	_{p=0.419 n=6}
_{Total Time}	_{18.963s (± 0.95%)}	_{18.871s (± 0.90%)}	_~	_18.722s	_19.180s	_{p=0.471 n=6}
_{self-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,394,272	_1,394,141	_{-131 (- 0.01%)}	_~	_~	_{p=0.001 n=6}
_Types	_442,245	_442,163	_{-82 (- 0.02%)}	_~	_~	_{p=0.001 n=6}
_{Memory Used}	_{1,654,170k (± 0.20%)}	_{1,654,799k (± 0.26%)}	_~	_1,650,410k	_1,660,203k	_{p=0.630 n=6}
_{Memory Allocs}	_{97,717,866 (± 0.05%)}	_{97,171,835 (± 0.06%)}	_{-546,032 (- 0.56%)}	_97,086,562	_97,229,271	_{p=0.005 n=6}
_{Config Time}	_{0.021s (±33.30%)}	_{0.018s (±36.05%)}	_~	_0.007s	_0.026s	_{p=0.423 n=6}
_{Parse Time}	_{0.274s (± 4.39%)}	_{0.274s (± 4.54%)}	_~	_0.261s	_0.293s	_{p=1.000 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{2.328s (± 0.82%)}	_{2.334s (± 0.97%)}	_~	_2.302s	_2.371s	_{p=0.689 n=6}
_{Emit Time}	_{0.305s (± 2.18%)}	_{0.311s (± 7.79%)}	_~	_0.293s	_0.358s	_{p=0.630 n=6}
_{Total Time}	_{30.685s (± 0.89%)}	_{30.636s (± 0.98%)}	_~	_30.303s	_31.121s	_{p=0.689 n=6}
_{self-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_337,637	_337,634	_{-3 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_199,520	_199,520	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{332,465k (± 0.04%)}	_{332,294k (± 0.02%)}	_{-171k (- 0.05%)}	_332,198k	_332,428k	_{p=0.045 n=6}
_{Memory Allocs}	_{4,717,664 (± 0.01%)}	_{4,682,110 (± 0.01%)}	_{-35,554 (- 0.75%)}	_4,681,207	_4,682,917	_{p=0.005 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.126s (± 5.61%)}	_{0.131s (± 4.21%)}	_~	_0.122s	_0.137s	_{p=0.227 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{1.389s (± 0.88%)}	_{1.393s (± 1.23%)}	_~	_1.363s	_1.409s	_{p=0.810 n=6}
_{Emit Time}	_{0.131s (±11.89%)}	_{0.128s (± 3.61%)}	_~	_0.123s	_0.137s	_{p=0.470 n=6}
_{Total Time}	_{1.704s (± 0.78%)}	_{1.705s (± 0.97%)}	_~	_1.678s	_1.727s	_{p=0.936 n=6}
_{ts-pre-modules - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_97,488	_97,488	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₅₆	₃₅₆	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{133,726k (± 0.02%)}	_{133,715k (± 0.03%)}	_~	_133,635k	_133,759k	_{p=1.000 n=6}
_{Memory Allocs}	_{180,328 (± 0.24%)}	_{180,141 (± 0.13%)}	_~	_179,843	_180,417	_{p=0.298 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.113s (± 4.58%)}	_{0.113s (± 5.19%)}	_~	_0.105s	_0.120s	_{p=1.000 n=6}
_{Bind Time}	_{0.040s (±11.39%)}	_{0.039s (± 9.68%)}	_~	_0.032s	_0.043s	_{p=0.462 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{0.157s (± 1.63%)}	_{0.156s (± 4.09%)}	_~	_0.148s	_0.164s	_{p=0.514 n=6}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_7,097,365	_7,097,303	_{-62 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_2,494,774	_2,494,761	_{-13 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory Used}	_{4,837,726k (± 0.02%)}	_{4,835,763k (± 0.03%)}	_{-1,963k (- 0.04%)}	_4,833,881k	_4,837,161k	_{p=0.013 n=6}
_{Memory Allocs}	_{33,116,878 (± 0.10%)}	_{32,795,962 (± 0.04%)}	_{-320,917 (- 0.97%)}	_32,775,296	_32,817,884	_{p=0.005 n=6}
_{Config Time}	_{0.075s (±10.74%)}	_{0.081s (± 6.51%)}	_~	_0.073s	_0.087s	_{p=0.199 n=6}
_{Parse Time}	_{0.916s (± 2.52%)}	_{0.923s (± 1.98%)}	_~	_0.905s	_0.949s	_{p=0.689 n=6}
_{Bind Time}	_{0.168s (±16.91%)}	_{0.155s (± 3.78%)}	_~	_0.150s	_0.164s	_{p=0.199 n=6}
_{Check Time}	_{9.102s (± 0.89%)}	_{9.173s (± 1.51%)}	_~	_9.069s	_9.395s	_{p=0.378 n=6}
_{Emit Time}	_{2.548s (± 7.62%)}	_{2.436s (± 9.27%)}	_~	_2.159s	_2.701s	_{p=0.378 n=6}
_{Total Time}	_{12.832s (± 0.89%)}	_{12.784s (± 0.96%)}	_~	_12.623s	_12.977s	_{p=0.378 n=6}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_188,078	_188,078	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{229,975k (± 0.19%)}	_{230,454k (± 0.09%)}	_~	_230,150k	_230,685k	_{p=0.066 n=6}
_{Memory Allocs}	_{952,920 (± 0.60%)}	_{958,546 (± 0.43%)}	_~	_953,927	_964,757	_{p=0.128 n=6}
_{Config Time}	_{0.013s (±14.68%)}	_{0.012s (±14.54%)}	_~	_0.009s	_0.014s	_{p=0.681 n=6}
_{Parse Time}	_{0.163s (± 3.42%)}	_{0.159s (± 2.70%)}	_~	_0.154s	_0.166s	_{p=0.199 n=6}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.047s (±18.73%)}	_{0.041s (± 8.01%)}	_~	_0.035s	_0.045s	_{p=0.257 n=6}
_{Total Time}	_{0.223s (± 4.32%)}	_{0.212s (± 1.92%)}	_{🟩-0.010s (- 4.71%)}	_0.207s	_0.217s	_{p=0.036 n=6}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,061,625	_1,061,625	_~	_~	_~	_{p=1.000 n=6}
_Types	_391,325	_391,325	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{644,999k (± 0.02%)}	_{644,384k (± 0.01%)}	_{-615k (- 0.10%)}	_644,330k	_644,470k	_{p=0.005 n=6}
_{Memory Allocs}	_{5,015,418 (± 0.05%)}	_{4,981,348 (± 0.15%)}	_{-34,069 (- 0.68%)}	_4,974,467	_4,990,942	_{p=0.005 n=6}
_{Config Time}	_{0.005s (±11.05%)}	_{0.005s (±17.48%)}	_~	_0.003s	_0.005s	_{p=0.752 n=6}
_{Parse Time}	_{0.137s (± 6.39%)}	_{0.137s (± 3.49%)}	_~	_0.131s	_0.144s	_{p=1.000 n=6}
_{Bind Time}	_{0.034s (±27.94%)}	_{0.032s (±25.29%)}	_~	_0.026s	_0.042s	_{p=0.573 n=6}
_{Check Time}	_{1.313s (± 0.57%)}	_{1.302s (± 0.51%)}	_~	_1.294s	_1.310s	_{p=0.054 n=6}
_{Emit Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.493s (± 0.97%)}	_{1.479s (± 0.69%)}	_~	_1.465s	_1.492s	_{p=0.065 n=6}

System info unknown

Hosts

native

Scenarios

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

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

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typescript-automation · 2026-07-10T21:04:35Z

Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 1000 repos with tsc comparing main and refs/pull/4591/merge:

Everything looks good!

…pescript-go#4591) Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: ahejlsberg <4226954+ahejlsberg@users.noreply.github.com>

Anders Hejlsberg (ahejlsberg) added 3 commits July 10, 2026 09:09

Sort by type depth in inferFromMatchingTypes function

d75360d

Accept new baselines

9d522df

Add regression test

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Copilot AI review requested due to automatic review settings July 10, 2026 19:22

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Fix spelling: maxinmum -> maximum in getTypeDepth comment

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Copilot finished work on behalf of Anders Hejlsberg (ahejlsberg) July 10, 2026 19:34

Jake Bailey (jakebailey) approved these changes Jul 21, 2026

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Anders Hejlsberg (ahejlsberg) enabled auto-merge July 21, 2026 15:40

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Merged via the queue into main with commit 90b40e8 Jul 21, 2026
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Anders Hejlsberg (ahejlsberg) deleted the fix-4462 branch July 21, 2026 16:11

Anders Hejlsberg (ahejlsberg) mentioned this pull request Jul 21, 2026

Generic type parameter inferred differently across two call-site positions with opposite variance (narrow type vs union) #4683

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Copilot AI mentioned this pull request Jul 31, 2026

[WIP] Fix false positive on generic type forwarded through interface #4812

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Theo Browne (t3dotgg) mentioned this pull request Oct 7, 2026

const type parameter + union return type: readonly [] not assignable to string[] (inherited from upstream, fixed there since) pingdotgg/ts-rust#13

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Paolo Valletta (paoValle) mentioned this pull request Oct 8, 2026

TS2322: const type parameter infers readonly [], rejected through a union return type (7.1.0-dev regression from typescript-go#4591) microsoft/TypeScript#64690

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Sort by type depth in `inferFromMatchingTypes` function - #4591

Sort by type depth in `inferFromMatchingTypes` function#4591
Anders Hejlsberg (ahejlsberg) merged 4 commits into
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fix-4462

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