Use tuple context based on apparent type of the contextual type uninstantiated by return mapper #62174

Andarist · 2025-08-01T22:04:17Z

fixes #62071

it's a somewhat cheap shot at this recent inference regression

…tantiated by return mapper

Copilot

Pull Request Overview

This PR fixes a recent inference regression related to tuple typing by improving contextual typing for array literals when return type mapping is involved. The change ensures that array literals receive proper tuple context even when the contextual type is instantiated by a return mapper.

Key changes:

Introduces a new SkipReturnMapper context flag to control when return mapper instantiation is applied
Modifies array literal checking to consider tuple context from both the standard contextual type and the contextual type without return mapper instantiation
Adds comprehensive test cases demonstrating the fix for both built-in and custom Promise implementations

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
`src/compiler/types.ts`	Adds new `SkipReturnMapper` context flag enum value
`src/compiler/checker.ts`	Implements the fix by modifying contextual type resolution and array literal checking logic
`tests/cases/compiler/returnTypeContextualTupleTyping1.ts`	Adds regression test cases for the tuple typing fix
`tests/baselines/reference/returnTypeContextualTupleTyping1.types`	Expected type output baseline for the new test
`tests/baselines/reference/returnTypeContextualTupleTyping1.symbols`	Expected symbol output baseline for the new test
`tests/baselines/reference/inferFromGenericFunctionReturnTypes3.types`	Updated baseline showing improved tuple inference behavior

Comments suppressed due to low confidence (2)

jakebailey · 2025-08-01T22:05:38Z

@typescript-bot test it

typescript-bot · 2025-08-01T22:05:43Z

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

typescript-bot · 2025-08-01T22:29:05Z

Hey @jakebailey, the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

typescript-bot · 2025-08-01T22:33:43Z

@jakebailey Here are the results of running the user tests with tsc comparing main and refs/pull/62174/merge:

Everything looks good!

typescript-bot · 2025-08-01T22:53:14Z

@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 - node (v18.15.0, x64)}
_Errors	₃₄	₃₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_62,370	_62,370	_~	_~	_~	_{p=1.000 n=6}
_Types	_50,386	_50,386	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{194,830k (± 0.96%)}	_{194,105k (± 0.94%)}	_~	_192,894k	_196,518k	_{p=0.128 n=6}
_{Parse Time}	_1.31s	_{1.30s (± 0.75%)}	_~	_1.29s	_1.31s	_{p=0.073 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.76s (± 0.28%)}	_{9.76s (± 0.39%)}	_~	_9.70s	_9.80s	_{p=0.936 n=6}
_{Emit Time}	_{2.73s (± 0.68%)}	_{2.73s (± 0.92%)}	_~	_2.71s	_2.77s	_{p=1.000 n=6}
_{Total Time}	_{14.52s (± 0.25%)}	_{14.52s (± 0.28%)}	_~	_14.48s	_14.58s	_{p=0.936 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,914	_948,914	_~	_~	_~	_{p=1.000 n=6}
_Types	_410,884	_410,885	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{1,226,397k (± 0.01%)}	_{1,226,390k (± 0.00%)}	_~	_1,226,360k	_1,226,483k	_{p=0.689 n=6}
_{Parse Time}	_{6.48s (± 0.18%)}	_{6.50s (± 0.29%)}	_~	_6.47s	_6.52s	_{p=0.250 n=6}
_{Bind Time}	_1.87s	_{1.87s (± 0.22%)}	_~	_1.87s	_1.88s	_{p=0.405 n=6}
_{Check Time}	_{32.09s (± 0.30%)}	_{32.15s (± 0.15%)}	_~	_32.11s	_32.24s	_{p=0.296 n=6}
_{Emit Time}	_{14.75s (± 0.71%)}	_{14.76s (± 0.20%)}	_~	_14.71s	_14.79s	_{p=0.746 n=6}
_{Total Time}	_{55.19s (± 0.34%)}	_{55.28s (± 0.14%)}	_~	_55.22s	_55.43s	_{p=0.470 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,543,160	_2,543,160	_~	_~	_~	_{p=1.000 n=6}
_Types	_900,384	_900,387	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,829,541k (± 0.01%)}	_{2,829,477k (± 0.01%)}	_~	_2,829,284k	_2,829,730k	_{p=0.521 n=6}
_{Parse Time}	_{8.75s (± 0.27%)}	_{8.77s (± 0.17%)}	_~	_8.75s	_8.79s	_{p=0.324 n=6}
_{Bind Time}	_{2.25s (± 0.37%)}	_{2.25s (± 0.91%)}	_~	_2.22s	_2.28s	_{p=0.933 n=6}
_{Check Time}	_{85.52s (± 0.32%)}	_{85.80s (± 0.34%)}	_~	_85.35s	_86.13s	_{p=0.065 n=6}
_{Emit Time}	_{0.96s (±104.98%)}	_{1.33s (±84.81%)}	_~	_0.30s	_2.42s	_{p=0.935 n=6}
_{Total Time}	_{97.49s (± 1.03%)}	_{98.15s (± 1.24%)}	_~	_96.68s	_99.57s	_{p=0.173 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,066	_1,227,080	_{+14 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,480	_267,487	_{+7 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,424,158k (± 6.16%)}	_{2,424,446k (± 6.16%)}	_~	_2,363,085k	_2,729,683k	_{p=0.689 n=6}
_{Parse Time}	_{5.19s (± 0.91%)}	_{5.21s (± 0.64%)}	_~	_5.17s	_5.27s	_{p=0.332 n=6}
_{Bind Time}	_{1.78s (± 1.09%)}	_{1.78s (± 0.83%)}	_~	_1.76s	_1.80s	_{p=0.684 n=6}
_{Check Time}	_{35.31s (± 0.39%)}	_{35.47s (± 0.64%)}	_~	_35.06s	_35.68s	_{p=0.065 n=6}
_{Emit Time}	_{2.99s (± 1.15%)}	_{2.98s (± 1.00%)}	_~	_2.93s	_3.01s	_{p=0.747 n=6}
_{Total Time}	_{45.28s (± 0.35%)}	_{45.45s (± 0.45%)}	_{+0.16s (+ 0.36%)}	_45.08s	_45.64s	_{p=0.045 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,066	_1,227,080	_{+14 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,480	_267,487	_{+7 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,919,704k (±12.89%)}	_{2,919,709k (±12.89%)}	_~	_2,433,022k	_3,163,510k	_{p=0.936 n=6}
_{Parse Time}	_{8.46s (± 1.03%)}	_{8.47s (± 1.03%)}	_~	_8.33s	_8.54s	_{p=0.575 n=6}
_{Bind Time}	_{2.68s (± 2.12%)}	_{2.70s (± 2.26%)}	_~	_2.61s	_2.78s	_{p=0.572 n=6}
_{Check Time}	_{53.16s (± 0.29%)}	_{53.24s (± 0.70%)}	_~	_52.68s	_53.67s	_{p=0.575 n=6}
_{Emit Time}	_{4.50s (± 1.09%)}	_{4.46s (± 2.95%)}	_~	_4.28s	_4.68s	_{p=0.471 n=6}
_{Total Time}	_{68.79s (± 0.19%)}	_{68.88s (± 0.64%)}	_~	_68.13s	_69.42s	_{p=0.298 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,555	_262,558	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_107,165	_107,168	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{441,963k (± 0.01%)}	_{442,039k (± 0.02%)}	_~	_441,894k	_442,152k	_{p=0.066 n=6}
_{Parse Time}	_{3.53s (± 0.99%)}	_{3.54s (± 0.89%)}	_~	_3.50s	_3.59s	_{p=0.520 n=6}
_{Bind Time}	_{1.32s (± 0.91%)}	_{1.32s (± 0.80%)}	_~	_1.30s	_1.33s	_{p=0.282 n=6}
_{Check Time}	_{18.97s (± 0.44%)}	_{18.97s (± 0.27%)}	_~	_18.90s	_19.03s	_{p=0.514 n=6}
_{Emit Time}	_{1.53s (± 1.01%)}	_{1.53s (± 1.22%)}	_~	_1.51s	_1.56s	_{p=0.681 n=6}
_{Total Time}	_{25.35s (± 0.30%)}	_{25.37s (± 0.31%)}	_~	_25.27s	_25.45s	_{p=0.747 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,367	_225,367	_~	_~	_~	_{p=1.000 n=6}
_Types	_94,290	_94,290	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{371,280k (± 0.06%)}	_{371,194k (± 0.02%)}	_~	_371,143k	_371,304k	_{p=0.810 n=6}
_{Parse Time}	_{2.90s (± 0.75%)}	_{2.89s (± 1.26%)}	_~	_2.84s	_2.93s	_{p=1.000 n=6}
_{Bind Time}	_{1.60s (± 1.88%)}	_{1.60s (± 1.71%)}	_~	_1.57s	_1.64s	_{p=1.000 n=6}
_{Check Time}	_{16.41s (± 0.38%)}	_{16.45s (± 0.27%)}	_~	_16.38s	_16.50s	_{p=0.199 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{20.90s (± 0.32%)}	_{20.94s (± 0.26%)}	_~	_20.86s	_21.00s	_{p=0.295 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁	₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,560,246	_3,560,373	_{+127 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_1,200,285	_1,200,349	_{+64 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,604,358k (± 0.01%)}	_{3,604,866k (± 0.04%)}	_~	_3,603,716k	_3,607,353k	_{p=0.575 n=6}
_{Parse Time}	_{15.28s (± 0.55%)}	_{15.27s (± 0.48%)}	_~	_15.22s	_15.42s	_{p=0.627 n=6}
_{Bind Time}	_{4.92s (± 0.65%)}	_{4.91s (± 0.64%)}	_~	_4.86s	_4.93s	_{p=0.560 n=6}
_{Check Time}	_{100.43s (± 1.65%)}	_{101.35s (± 1.67%)}	_~	_98.59s	_102.88s	_{p=0.378 n=6}
_{Emit Time}	_{34.13s (±24.68%)}	_{34.85s (±12.76%)}	_~	_30.86s	_41.55s	_{p=0.093 n=6}
_{Total Time}	_{154.76s (± 4.99%)}	_{156.38s (± 2.98%)}	_~	_151.16s	_164.19s	_{p=0.173 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_321,136	_321,142	_{+6 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_140,173	_140,174	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{477,390k (± 0.02%)}	_{477,427k (± 0.02%)}	_~	_477,317k	_477,545k	_{p=0.378 n=6}
_{Parse Time}	_{4.30s (± 0.57%)}	_{4.30s (± 0.27%)}	_~	_4.29s	_4.32s	_{p=0.740 n=6}
_{Bind Time}	_{1.80s (± 0.91%)}	_{1.79s (± 0.76%)}	_~	_1.77s	_1.81s	_{p=0.060 n=6}
_{Check Time}	_{20.58s (± 0.13%)}	_{20.62s (± 0.25%)}	_~	_20.58s	_20.72s	_{p=0.124 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=1.000 n=6}
_{Total Time}	_{26.69s (± 0.15%)}	_{26.70s (± 0.17%)}	_~	_26.66s	_26.79s	_{p=0.872 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_663,079	_663,132	_{+53 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_Types	_197,935	_197,938	_{+3 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{569,968k (± 0.02%)}	_{570,133k (± 0.02%)}	_{+165k (+ 0.03%)}	_569,887k	_570,250k	_{p=0.037 n=6}
_{Parse Time}	_{4.28s (± 1.43%)}	_{4.27s (± 1.14%)}	_~	_4.21s	_4.35s	_{p=0.572 n=6}
_{Bind Time}	_{1.32s (± 0.78%)}	_{1.33s (± 0.77%)}	_~	_1.32s	_1.35s	_{p=0.134 n=6}
_{Check Time}	_{20.29s (± 1.57%)}	_{19.97s (± 1.71%)}	_~	_19.80s	_20.67s	_{p=0.109 n=6}
_{Emit Time}	_{0.00s (±154.76%)}	_{0.00s (±244.70%)}	_~	_0.00s	_0.01s	_{p=0.595 n=6}
_{Total Time}	_{25.89s (± 1.37%)}	_{25.57s (± 1.36%)}	_~	_25.37s	_26.28s	_{p=0.173 n=6}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

Compiler-Unions - node (v18.15.0, x64)
angular-1 - node (v18.15.0, x64)
mui-docs - node (v18.15.0, x64)
self-build-src - node (v18.15.0, x64)
self-build-src-public-api - node (v18.15.0, x64)
self-compiler - node (v18.15.0, x64)
ts-pre-modules - node (v18.15.0, x64)
vscode - node (v18.15.0, x64)
webpack - node (v18.15.0, x64)
xstate-main - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

typescript-bot · 2025-08-01T23:50:09Z

@jakebailey Here are the results of running the top 400 repos with tsc comparing main and refs/pull/62174/merge:

Something interesting changed - please have a look.

Details

typeorm/typeorm

tsconfig.json

error TS2352: Conversion of type '[ObjectLiteral | null, ObjectLiteral | null]' to type 'Post[]' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
- test/github-issues/4156/issue-4156.ts#L47
- test/github-issues/4156/issue-4156.ts#L76

Andarist · 2025-08-02T08:17:57Z

repro for the above break: TS playground,

EDIT:// and its smaller version: TS playground

Andarist · 2025-08-02T19:18:05Z

I think the above cast in the repro case should just be allowed. I opened a new issue about this: #62177

i-ayushh18 · 2025-08-02T19:37:23Z

🤖 AI Assistant: Task completed: PR #62174: Use tuple context based on apparent type of the contextual type uninstantiated by return ...

Use tuple context based on apparent type of the contextual type unins…

472aaaf

…tantiated by return mapper

Copilot AI review requested due to automatic review settings August 1, 2025 22:04

github-project-automation bot added this to PR Backlog Aug 1, 2025

github-project-automation bot moved this to Not started in PR Backlog Aug 1, 2025

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Use tuple context based on apparent type of the contextual type uninstantiated by return mapper #62174

Use tuple context based on apparent type of the contextual type uninstantiated by return mapper #62174

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Use tuple context based on apparent type of the contextual type uninstantiated by return mapper #62174

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