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Improve contextual types inferred from return types#61913

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ahejlsberg commentedJun 22, 2025

Implements the experiment discussedhere.

ahejlsberg added2 commits

June 22, 2025 16:08

Improve contextual types inferred from return types

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June 22, 2025 20:10

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Jun 22, 2025

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Pull Request Overview

This PR improves contextual type inference by introducing a new inference priority for mapping return types.

Added a new enum member ReturnMapper and updated the MaxValue and combination mask in InferencePriority.
Modified the type-checker to exclude any/unknown types when using the ReturnMapper inference and passed the new flag into the inferTypes function.

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
src/compiler/types.ts	Added ReturnMapper to the InferencePriority enum and updated related bit masks.
src/compiler/checker.ts	Updated inference filtering to exclude any/unknown types and passed the ReturnMapper flag to inferTypes.

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typescript-bot commentedJun 22, 2025

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document themon our wiki's API Breaking Changes page.

Also, please make sure@DanielRosenwasser and@RyanCavanaugh are aware of the changes, just as a heads up.

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ahejlsberg commentedJun 22, 2025

@typescript-bot test it

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typescript-bot commentedJun 22, 2025•
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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

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typescript-bot commentedJun 22, 2025

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

Everything looks the same!

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typescript-bot commentedJun 22, 2025

@ahejlsberg Here are the results of running the user tests with tsc comparingmain andrefs/pull/61913/merge:

Everything looks good!

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typescript-bot commentedJun 22, 2025

@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 - 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}	_{194,094k (± 0.95%)}	_{193,548k (± 0.77%)}	_~	_192,815k	_196,567k	_{p=0.378 n=6}
_{Parse Time}	_{1.31s (± 0.31%)}	_{1.30s (± 0.75%)}	_~	_1.29s	_1.31s	_{p=0.213 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.69s (± 0.29%)}	_{9.66s (± 0.22%)}	_~	_9.63s	_9.69s	_{p=0.077 n=6}
_{Emit Time}	_{2.74s (± 0.93%)}	_{2.73s (± 1.40%)}	_~	_2.67s	_2.77s	_{p=1.000 n=6}
_{Total Time}	_{14.46s (± 0.17%)}	_{14.42s (± 0.33%)}	_~	_14.37s	_14.49s	_{p=0.169 n=6}
_{angular-1 - node (v18.15.0, x64)}
_Errors	₅₆	₅₆	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_948,750	_948,576	_{-174 (- 0.02%)}	_~	_~	_{p=0.001 n=6}
_Types	_410,846	_410,804	_{-42 (- 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{1,224,589k (± 0.01%)}	_{1,224,440k (± 0.00%)}	_{-149k (- 0.01%)}	_1,224,395k	_1,224,531k	_{p=0.008 n=6}
_{Parse Time}	_{6.62s (± 0.50%)}	_{6.64s (± 0.98%)}	_~	_6.55s	_6.70s	_{p=0.377 n=6}
_{Bind Time}	_{1.89s (± 0.93%)}	_{1.89s (± 0.33%)}	_~	_1.88s	_1.90s	_{p=1.000 n=6}
_{Check Time}	_{31.83s (± 0.14%)}	_{31.79s (± 0.27%)}	_~	_31.65s	_31.88s	_{p=0.470 n=6}
_{Emit Time}	_{14.87s (± 0.57%)}	_{14.90s (± 0.42%)}	_~	_14.84s	_14.99s	_{p=0.520 n=6}
_{Total Time}	_{55.20s (± 0.12%)}	_{55.22s (± 0.21%)}	_~	_55.02s	_55.33s	_{p=0.575 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,561,658	_2,561,485	_{-173 (- 0.01%)}	_~	_~	_{p=0.001 n=6}
_Types	_892,631	_892,606	_{-25 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,836,579k (± 0.00%)}	_{2,836,448k (± 0.00%)}	_{-130k (- 0.00%)}	_2,836,398k	_2,836,529k	_{p=0.013 n=6}
_{Parse Time}	_{9.20s (± 0.50%)}	_{9.18s (± 0.25%)}	_~	_9.14s	_9.20s	_{p=0.571 n=6}
_{Bind Time}	_{2.30s (± 0.22%)}	_{2.31s (± 0.33%)}	_~	_2.30s	_2.32s	_{p=0.247 n=6}
_{Check Time}	_{83.62s (± 0.32%)}	_{83.67s (± 0.64%)}	_~	_82.96s	_84.42s	_{p=0.873 n=6}
_{Emit Time}	_{0.30s (± 1.37%)}	_{0.30s (± 1.37%)}	_~	_0.29s	_0.30s	_{p=1.000 n=6}
_{Total Time}	_{95.41s (± 0.29%)}	_{95.45s (± 0.58%)}	_~	_94.73s	_96.21s	_{p=0.810 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,126	_1,227,160	_{+34 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,408	_267,426	_{+18 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,362,056k (± 0.02%)}	_{2,422,890k (± 6.15%)}	_~	_2,361,445k	_2,727,187k	_{p=0.689 n=6}
_{Parse Time}	_{5.20s (± 0.72%)}	_{5.20s (± 1.00%)}	_~	_5.10s	_5.25s	_{p=0.747 n=6}
_{Bind Time}	_{1.80s (± 0.29%)}	_{1.80s (± 0.42%)}	_~	_1.79s	_1.81s	_{p=0.784 n=6}
_{Check Time}	_{35.12s (± 0.19%)}	_{35.05s (± 0.44%)}	_~	_34.76s	_35.19s	_{p=0.377 n=6}
_{Emit Time}	_{3.03s (± 4.41%)}	_{2.96s (± 1.02%)}	_~	_2.93s	_3.02s	_{p=0.298 n=6}
_{Total Time}	_{45.16s (± 0.35%)}	_{45.03s (± 0.30%)}	_~	_44.82s	_45.17s	_{p=0.230 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,126	_1,227,160	_{+34 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,408	_267,426	_{+18 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,700,732k (±13.34%)}	_{2,796,386k (±14.25%)}	_~	_2,431,816k	_3,162,628k	_{p=0.575 n=6}
_{Parse Time}	_{6.85s (± 1.83%)}	_{6.86s (± 1.24%)}	_~	_6.77s	_6.95s	_{p=0.689 n=6}
_{Bind Time}	_{2.20s (± 2.23%)}	_{2.20s (± 1.37%)}	_~	_2.16s	_2.25s	_{p=1.000 n=6}
_{Check Time}	_{42.60s (± 1.09%)}	_{42.62s (± 0.59%)}	_~	_42.40s	_42.94s	_{p=0.630 n=6}
_{Emit Time}	_{3.61s (± 3.93%)}	_{3.46s (± 1.38%)}	_{🟩-0.15s (- 4.06%)}	_3.41s	_3.55s	_{p=0.045 n=6}
_{Total Time}	_{55.25s (± 0.98%)}	_{55.12s (± 0.55%)}	_~	_54.83s	_55.46s	_{p=0.810 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,474	_262,470	_{-4 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_107,135	_107,127	_{-8 (- 0.01%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{441,755k (± 0.01%)}	_{441,712k (± 0.01%)}	_~	_441,640k	_441,809k	_{p=0.230 n=6}
_{Parse Time}	_{3.51s (± 1.70%)}	_{3.55s (± 1.31%)}	_~	_3.50s	_3.60s	_{p=0.126 n=6}
_{Bind Time}	_{1.31s (± 1.25%)}	_{1.32s (± 0.83%)}	_~	_1.31s	_1.34s	_{p=0.188 n=6}
_{Check Time}	_{18.83s (± 0.45%)}	_{18.82s (± 0.23%)}	_~	_18.77s	_18.88s	_{p=1.000 n=6}
_{Emit Time}	_{1.52s (± 0.77%)}	_{1.51s (± 0.91%)}	_~	_1.50s	_1.54s	_{p=0.564 n=6}
_{Total Time}	_{25.17s (± 0.49%)}	_{25.20s (± 0.28%)}	_~	_25.11s	_25.29s	_{p=0.296 n=6}
_{ts-pre-modules - node (v18.15.0, x64)}
_Errors	₇₁	₇₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_225,327	_225,354	_{+27 (+ 0.01%)}	_~	_~	_{p=0.001 n=6}
_Types	_94,288	_94,289	_{+1 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{371,169k (± 0.03%)}	_{371,112k (± 0.02%)}	_~	_371,048k	_371,239k	_{p=0.378 n=6}
_{Parse Time}	_{2.90s (± 1.17%)}	_{2.88s (± 0.90%)}	_~	_2.84s	_2.91s	_{p=0.418 n=6}
_{Bind Time}	_{1.60s (± 0.61%)}	_{1.61s (± 2.00%)}	_~	_1.56s	_1.64s	_{p=0.373 n=6}
_{Check Time}	_{16.36s (± 0.28%)}	_{16.26s (± 0.31%)}	_{-0.10s (- 0.61%)}	_16.20s	_16.35s	_{p=0.020 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{20.86s (± 0.33%)}	_{20.75s (± 0.43%)}	_~	_20.65s	_20.88s	_{p=0.092 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₃₃	₃₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,478,623	_3,478,628	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_1,170,082	_1,170,057	_{-25 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,526,701k (± 0.01%)}	_{3,526,781k (± 0.01%)}	_~	_3,526,343k	_3,527,039k	_{p=0.378 n=6}
_{Parse Time}	_{15.06s (± 0.59%)}	_{15.08s (± 0.53%)}	_~	_14.98s	_15.16s	_{p=0.629 n=6}
_{Bind Time}	_{4.87s (± 0.53%)}	_{4.85s (± 0.38%)}	_~	_4.83s	_4.88s	_{p=0.223 n=6}
_{Check Time}	_{98.25s (± 3.23%)}	_{96.25s (± 3.35%)}	_~	_93.12s	_100.63s	_{p=0.298 n=6}
_{Emit Time}	_{30.39s (± 2.82%)}	_{30.37s (± 4.16%)}	_~	_29.34s	_32.54s	_{p=0.936 n=6}
_{Total Time}	_{148.57s (± 2.63%)}	_{146.57s (± 2.88%)}	_~	_142.59s	_151.35s	_{p=0.470 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_320,000	_320,000	_~	_~	_~	_{p=1.000 n=6}
_Types	_140,356	_140,355	_{-1 (- 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{474,123k (± 0.01%)}	_{474,190k (± 0.02%)}	_~	_474,041k	_474,306k	_{p=0.199 n=6}
_{Parse Time}	_{4.33s (± 0.71%)}	_{4.33s (± 0.79%)}	_~	_4.28s	_4.37s	_{p=0.936 n=6}
_{Bind Time}	_{1.77s (± 1.21%)}	_{1.78s (± 1.17%)}	_~	_1.75s	_1.80s	_{p=0.871 n=6}
_{Check Time}	_{20.67s (± 0.29%)}	_{20.66s (± 0.55%)}	_~	_20.57s	_20.85s	_{p=0.686 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{26.76s (± 0.26%)}	_{26.77s (± 0.36%)}	_~	_26.68s	_26.93s	_{p=1.000 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_667,374	_667,148	_{-226 (- 0.03%)}	_~	_~	_{p=0.001 n=6}
_Types	_198,751	_198,664	_{-87 (- 0.04%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{570,150k (± 0.00%)}	_{570,009k (± 0.02%)}	_~	_569,915k	_570,225k	_{p=0.066 n=6}
_{Parse Time}	_{5.54s (± 0.56%)}	_{5.51s (± 1.13%)}	_~	_5.43s	_5.57s	_{p=0.809 n=6}
_{Bind Time}	_{1.65s (± 0.54%)}	_{1.66s (± 0.38%)}	_~	_1.65s	_1.67s	_{p=0.070 n=6}
_{Check Time}	_{25.33s (± 0.28%)}	_{25.25s (± 1.43%)}	_~	_24.52s	_25.49s	_{p=0.520 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{32.51s (± 0.17%)}	_{32.42s (± 1.08%)}	_~	_31.73s	_32.69s	_{p=0.809 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:

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typescript-bot commentedJun 22, 2025

@ahejlsberg Here are the results of running the top 400 repos with tsc comparingmain andrefs/pull/61913/merge:

Something interesting changed - please have a look.

Details

github/docs

1 of 2 projects failed to build with the old tsc and were ignored

tsconfig.json

error TS2739: Type '{ productVideo: any; productVideoTranscript: any; hasGuidesPage: any; product: { href: any; title: any; }; whatsNewChangelog: any; changelogUrl: any; productCommunityExamples: any; ghesReleases: any; ... 6 more ...; shortTitle: any; }' is missing the following properties from type 'ProductLandingContextT': introPlainText, intro, beta_product
- src/landings/components/ProductLandingContext.tsx#L119

gvergnaud/ts-pattern

tests/tsconfig.json

error TS2578: Unused '@ts-expect-error' directive.
- tests/types.test.ts#L403
- tests/types.test.ts#L417
error TS2344: Type 'false' does not satisfy the constraint 'true'.
- tests/when.test.ts#L218

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Andarist commentedJun 22, 2025

This PR addresses a different situation, but its generic title reminded me of#58910 ;p

Andarist reviewed

Jun 22, 2025

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src/compiler/types.ts

		@@ -7129,6 +7130,7 @@ export const enum InferenceFlags {
		NoDefault = 1 << 0, // Infer silentNeverType for no inferences (otherwise anyType or unknownType)
		AnyDefault = 1 << 1, // Infer anyType (in JS files) for no inferences (otherwise unknownType)
		SkippedGenericFunction = 1 << 2, // A generic function was skipped during inference
		NoUnknownInference = 1 << 3,

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AndaristJun 22, 2025

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nit: this stays unused

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Andarist commentedJun 23, 2025

Minimal repro case for thegithub/docs problem:

typeMany<T>=T|readonlyT[];declarefunctionpick<Textendsobject,UextendskeyofT>(object:T,  ...props:Array<Many<U>>):Pick<T,U>;typeProductLandingContextT={title:string;intro:string;};constgetProductLandingContextFromRequest=async(req:any,):Promise<ProductLandingContextT>=>{constpage=req.context.page;consttitle=awaitpage.renderProp("title",req.context,{textOnly:true});return{    title,    ...pick(page,["intro"]),};};

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jakebailey commentedJun 23, 2025

@typescript-bot pack this

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typescript-bot commentedJun 23, 2025•
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Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`pack this`	✅ Started	✅ Results

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typescript-bot commentedJun 23, 2025•
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Hey@jakebailey, I've packed this intoan installable tgz. You can install it for testing by referencing it in yourpackage.json like so:

{    "devDependencies": {        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/165448/artifacts?artifactName=tgz&fileId=BEE85749DC012DFE0439FCB8B8A57B4EE5CFE5CE56B343DD2C6737B725BE3D7C02&fileName=/typescript-5.9.0-insiders.20250623.tgz"    }}

and then runningnpm install.

There is also a playgroundfor this build and annpm module you can use via"typescript": "npm:@typescript-deploys/pr-build@5.9.0-pr-61913-11".;

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Author: Team For Uncommitted Bug

PR for untriaged, rejected, closed or missing bug

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Improve contextual types inferred from return types#61913

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Improve contextual types inferred from return types#61913

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ahejlsberg commentedJun 22, 2025

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Pull Request Overview

Reviewed Changes

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tsc

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typescript-bot commentedJun 22, 2025

github/docs

tsconfig.json

gvergnaud/ts-pattern

tests/tsconfig.json

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