Combine inferences from distributive conditional types #62093

Andarist · 2025-07-20T10:52:29Z

fixes #62079

typescript-bot · 2025-07-20T10:52:42Z

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

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

Copilot

Pull Request Overview

This PR implements a fix for TypeScript issue #62079 by combining inferences from distributive conditional types. The change modifies the type inference system to properly handle parameters that use distributive conditional types, ensuring that inferences from multiple union member distributions are correctly combined.

Adds a new DistributiveConditional inference priority flag to track distributive conditional type inferences
Modifies inference priority logic to combine distributive conditional inferences with other priorities
Updates the conditional type inference process to mark distributive conditional types with the new priority

Reviewed Changes

Copilot reviewed 5 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 `DistributiveConditional` inference priority flag and includes it in combination logic
`src/compiler/checker.ts`	Implements distributive conditional inference tracking and priority combination logic
`tests/cases/compiler/genericFunctionParametersConditionalType1.ts`	Test case demonstrating the fix for distributive conditional type parameter inference
`tests/baselines/reference/genericFunctionParametersConditionalType1.types`	Expected type output showing proper union distribution in parameter types
`tests/baselines/reference/genericFunctionParametersConditionalType1.symbols`	Expected symbol resolution output for the test case

Comments suppressed due to low confidence (1)

Andarist · 2025-07-20T10:55:42Z

src/compiler/checker.ts

@@ -26784,13 +26784,18 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                        if (candidate === blockedStringType) {
                            return;
                        }
-                        if (inference.priority === undefined || priority < inference.priority) {
+                        const combinedPriority = priority | (inference.individualPriority || InferencePriority.None);


I don't quite like how this turned out - I probably should move this thing to a separate InferenceInfo property (similar to topLevel) instead of shoving it into .priority.

That said, those changes would be cosmetic and wouldn't really change the idea behind this fix. In the meantime, I'd love to see what user/top tests have to say about this (cc @jakebailey )

RyanCavanaugh · 2025-07-21T18:58:09Z

@typescript-bot test it

typescript-bot · 2025-07-21T18:58:14Z

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 · 2025-07-21T19:23:01Z

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

Everything looks the same!

You can check the log here.

typescript-bot · 2025-07-21T19:24:54Z

@RyanCavanaugh Here are the results of running the user tests with tsc comparing main and refs/pull/62093/merge:

Something interesting changed - please have a look.

Details

effect

packages/effect/benchmark/tsconfig.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764

tsconfig.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.src.json
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.build.json

tsconfig.build.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.build.json

packages/typeclass/dtslint/tsconfig.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.src.json

packages/platform/dtslint/tsconfig.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.src.json

packages/effect/dtslint/tsconfig.json

[NEW] error TS2322: Type 'transformOrFail<S, SchemaClass<any, any, never> | S, FD>' is not assignable to type 'filterEffect<S, FD>'.
- packages/effect/src/Schema.ts#L3764 in packages/effect/tsconfig.src.json

webpack

tsconfig.types.test.json

[NEW] error TS2345: Argument of type 'HookMap<SyncBailHook<T, R, UnsetAdditionalOptions>>' is not assignable to parameter of type 'HookMap<SyncBailHook<T | [...AsArray<T>], R, UnsetAdditionalOptions>>'.

tsconfig.types.json

[NEW] error TS2345: Argument of type 'HookMap<SyncBailHook<T, R, UnsetAdditionalOptions>>' is not assignable to parameter of type 'HookMap<SyncBailHook<T | [...AsArray<T>], R, UnsetAdditionalOptions>>'.

tsconfig.json

[NEW] error TS2345: Argument of type 'HookMap<SyncBailHook<T, R, UnsetAdditionalOptions>>' is not assignable to parameter of type 'HookMap<SyncBailHook<T | [...AsArray<T>], R, UnsetAdditionalOptions>>'.

typescript-bot · 2025-07-21T19:44:24Z

@RyanCavanaugh
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}	_{193,573k (± 0.76%)}	_{194,753k (± 1.04%)}	_~	_192,901k	_196,743k	_{p=0.575 n=6}
_{Parse Time}	_{1.30s (± 0.64%)}	_{1.30s (± 0.79%)}	_~	_1.29s	_1.31s	_{p=0.923 n=6}
_{Bind Time}	_0.73s	_0.73s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{9.75s (± 0.40%)}	_{9.74s (± 0.22%)}	_~	_9.71s	_9.77s	_{p=0.260 n=6}
_{Emit Time}	_{2.74s (± 0.78%)}	_{2.75s (± 0.69%)}	_~	_2.73s	_2.78s	_{p=0.511 n=6}
_{Total Time}	_{14.52s (± 0.30%)}	_{14.52s (± 0.13%)}	_~	_14.50s	_14.54s	_{p=0.513 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	_410,884	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{1,226,389k (± 0.00%)}	_{1,226,395k (± 0.01%)}	_~	_1,226,322k	_1,226,495k	_{p=0.936 n=6}
_{Parse Time}	_{6.53s (± 1.02%)}	_{6.52s (± 0.85%)}	_~	_6.46s	_6.62s	_{p=1.000 n=6}
_{Bind Time}	_{1.87s (± 0.44%)}	_1.87s	_~	_~	_~	_{p=0.290 n=6}
_{Check Time}	_{32.00s (± 0.27%)}	_{31.97s (± 0.31%)}	_~	_31.88s	_32.10s	_{p=0.748 n=6}
_{Emit Time}	_{14.86s (± 0.97%)}	_{14.85s (± 0.59%)}	_~	_14.74s	_14.94s	_{p=0.688 n=6}
_{Total Time}	_{55.26s (± 0.30%)}	_{55.21s (± 0.22%)}	_~	_55.02s	_55.36s	_{p=0.423 n=6}
_{mui-docs - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_2,542,899	_2,542,993	_{+94 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_900,428	_900,433	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,829,362k (± 0.00%)}	_{2,829,402k (± 0.01%)}	_~	_2,829,202k	_2,829,600k	_{p=0.688 n=6}
_{Parse Time}	_{8.76s (± 0.29%)}	_{8.75s (± 0.22%)}	_~	_8.72s	_8.77s	_{p=0.683 n=6}
_{Bind Time}	_{2.26s (± 0.23%)}	_{2.24s (± 0.36%)}	_{-0.01s (- 0.59%)}	_2.23s	_2.25s	_{p=0.014 n=6}
_{Check Time}	_{85.74s (± 0.31%)}	_{85.56s (± 0.49%)}	_~	_84.98s	_86.20s	_{p=0.378 n=6}
_{Emit Time}	_{0.59s (±119.68%)}	_{1.01s (±95.34%)}	_~	_0.30s	_2.24s	_{p=0.184 n=6}
_{Total Time}	_{97.35s (± 0.86%)}	_{97.56s (± 0.75%)}	_~	_96.64s	_98.57s	_{p=0.575 n=6}
_{self-build-src - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,048	_1,227,076	_{+28 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,470	_267,475	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{2,363,435k (± 0.01%)}	_{2,363,612k (± 0.02%)}	_~	_2,363,060k	_2,364,027k	_{p=0.378 n=6}
_{Parse Time}	_{5.21s (± 1.05%)}	_{5.21s (± 1.13%)}	_~	_5.14s	_5.30s	_{p=0.872 n=6}
_{Bind Time}	_{1.80s (± 0.84%)}	_{1.79s (± 1.62%)}	_~	_1.76s	_1.83s	_{p=0.684 n=6}
_{Check Time}	_{35.34s (± 0.46%)}	_{35.43s (± 0.45%)}	_~	_35.23s	_35.68s	_{p=0.298 n=6}
_{Emit Time}	_{2.98s (± 1.32%)}	_{2.97s (± 0.88%)}	_~	_2.93s	_3.00s	_{p=0.630 n=6}
_{Total Time}	_{45.34s (± 0.37%)}	_{45.41s (± 0.40%)}	_~	_45.21s	_45.71s	_{p=0.575 n=6}
_{self-build-src-public-api - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,227,048	_1,227,076	_{+28 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_267,470	_267,475	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{3,039,849k (± 9.77%)}	_{3,161,978k (± 0.02%)}	_~	_3,161,210k	_3,162,728k	_{p=0.093 n=6}
_{Parse Time}	_{8.50s (± 1.20%)}	_{8.55s (± 0.46%)}	_~	_8.51s	_8.61s	_{p=0.575 n=6}
_{Bind Time}	_{2.66s (± 1.80%)}	_{2.64s (± 0.95%)}	_~	_2.61s	_2.67s	_{p=0.689 n=6}
_{Check Time}	_{53.22s (± 0.48%)}	_{53.26s (± 0.23%)}	_~	_53.10s	_53.45s	_{p=0.936 n=6}
_{Emit Time}	_{4.46s (± 2.87%)}	_{4.34s (± 2.32%)}	_~	_4.21s	_4.45s	_{p=0.090 n=6}
_{Total Time}	_{68.83s (± 0.48%)}	_{68.79s (± 0.21%)}	_~	_68.66s	_69.05s	_{p=0.936 n=6}
_{self-compiler - node (v18.15.0, x64)}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_262,548	_262,554	_{+6 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_Types	_107,156	_107,161	_{+5 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{441,929k (± 0.01%)}	_{441,933k (± 0.01%)}	_~	_441,855k	_442,020k	_{p=0.936 n=6}
_{Parse Time}	_{3.56s (± 0.75%)}	_{3.52s (± 0.61%)}	_{-0.04s (- 1.22%)}	_3.49s	_3.55s	_{p=0.024 n=6}
_{Bind Time}	_{1.32s (± 1.07%)}	_{1.32s (± 0.89%)}	_~	_1.30s	_1.33s	_{p=0.934 n=6}
_{Check Time}	_{18.96s (± 0.39%)}	_{18.94s (± 0.46%)}	_~	_18.86s	_19.10s	_{p=0.328 n=6}
_{Emit Time}	_{1.52s (± 0.68%)}	_{1.53s (± 1.36%)}	_~	_1.49s	_1.55s	_{p=0.677 n=6}
_{Total Time}	_{25.36s (± 0.33%)}	_{25.30s (± 0.30%)}	_~	_25.25s	_25.44s	_{p=0.170 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}	_{371,155k (± 0.03%)}	_{371,137k (± 0.02%)}	_~	_371,062k	_371,229k	_{p=1.000 n=6}
_{Parse Time}	_{2.87s (± 0.72%)}	_{2.89s (± 0.99%)}	_~	_2.84s	_2.92s	_{p=0.257 n=6}
_{Bind Time}	_{1.59s (± 1.45%)}	_{1.61s (± 0.94%)}	_~	_1.59s	_1.63s	_{p=0.243 n=6}
_{Check Time}	_{16.45s (± 0.27%)}	_{16.45s (± 0.38%)}	_~	_16.36s	_16.51s	_{p=0.936 n=6}
_{Emit Time}	_0.00s	_0.00s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{20.92s (± 0.30%)}	_{20.95s (± 0.36%)}	_~	_20.85s	_21.02s	_{p=0.423 n=6}
_{vscode - node (v18.15.0, x64)}
_Errors	₁	₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_3,524,145	_3,524,145	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,189,792	_1,189,792	_~	_~	_~	_{p=1.000 n=6}
_{Memory used}	_{3,573,696k (± 0.00%)}	_{3,573,744k (± 0.00%)}	_~	_3,573,612k	_3,574,010k	_{p=0.936 n=6}
_{Parse Time}	_{15.09s (± 0.25%)}	_{15.31s (± 3.24%)}	_~	_15.03s	_16.31s	_{p=0.518 n=6}
_{Bind Time}	_{4.89s (± 0.56%)}	_{4.93s (± 0.70%)}	_~	_4.89s	_4.97s	_{p=0.063 n=6}
_{Check Time}	_{101.49s (± 2.87%)}	_{99.85s (± 0.91%)}	_~	_99.03s	_101.54s	_{p=0.298 n=6}
_{Emit Time}	_{31.45s (± 6.16%)}	_{30.51s (± 0.72%)}	_~	_30.17s	_30.82s	_{p=0.575 n=6}
_{Total Time}	_{152.91s (± 1.99%)}	_{150.60s (± 0.79%)}	_~	_149.19s	_152.16s	_{p=0.173 n=6}
_{webpack - node (v18.15.0, x64)}
_Errors	₂	₇	_{🔻+5 (+250.00%)}	_~	_~	_{p=0.001 n=6}
_Symbols	_320,541	_330,861	_{+10,320 (+ 3.22%)}	_~	_~	_{p=0.001 n=6}
_Types	_140,016	_146,362	_{🔻+6,346 (+ 4.53%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{476,527k (± 0.04%)}	_{483,704k (± 0.02%)}	_{+7,176k (+ 1.51%)}	_483,576k	_483,847k	_{p=0.005 n=6}
_{Parse Time}	_{4.31s (± 0.54%)}	_{4.30s (± 0.74%)}	_~	_4.25s	_4.35s	_{p=0.935 n=6}
_{Bind Time}	_{1.80s (± 0.97%)}	_{1.79s (± 1.29%)}	_~	_1.75s	_1.82s	_{p=0.567 n=6}
_{Check Time}	_{20.60s (± 0.40%)}	_{20.91s (± 0.45%)}	_{+0.31s (+ 1.49%)}	_20.83s	_21.07s	_{p=0.005 n=6}
_{Emit Time}	_0.00s	_{0.00s (±154.76%)}	_~	_0.00s	_0.01s	_{p=0.174 n=6}
_{Total Time}	_{26.71s (± 0.33%)}	_{27.00s (± 0.49%)}	_{+0.29s (+ 1.08%)}	_26.85s	_27.21s	_{p=0.006 n=6}
_{xstate-main - node (v18.15.0, x64)}
_Errors	₃₀	₃₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_662,663	_662,663	_~	_~	_~	_{p=1.000 n=6}
_Types	_197,635	_197,637	_{+2 (+ 0.00%)}	_~	_~	_{p=0.001 n=6}
_{Memory used}	_{569,834k (± 0.02%)}	_{569,778k (± 0.02%)}	_~	_569,601k	_569,883k	_{p=0.810 n=6}
_{Parse Time}	_{4.27s (± 0.53%)}	_{4.25s (± 0.51%)}	_~	_4.22s	_4.28s	_{p=0.366 n=6}
_{Bind Time}	_{1.32s (± 0.88%)}	_{1.33s (± 0.88%)}	_~	_1.31s	_1.34s	_{p=0.357 n=6}
_{Check Time}	_{19.96s (± 1.38%)}	_{20.08s (± 1.58%)}	_~	_19.79s	_20.53s	_{p=0.336 n=6}
_{Emit Time}	_{0.00s (±244.70%)}	_0.00s	_~	_~	_~	_{p=0.405 n=6}
_{Total Time}	_{25.55s (± 1.10%)}	_{25.66s (± 1.32%)}	_~	_25.33s	_26.12s	_{p=0.689 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 · 2025-07-21T20:45:33Z

@RyanCavanaugh Here are the results of running the top 400 repos with tsc comparing main and refs/pull/62093/merge:

Something interesting changed - please have a look.

Details

TanStack/query

78 of 118 projects failed to build with the old tsc and were ignored

packages/vue-query/tsconfig.prod.json

error TS2344: Type '{ wow: boolean; }' does not satisfy the constraint '"Expected: ..., Actual: function"'.
error TS2344: Type '{ wow: boolean; } | undefined' does not satisfy the constraint '"Expected: ..., Actual: function" | "Expected: undefined, Actual: function"'.
- packages/vue-query/src/__tests__/queryOptions.test-d.ts#L180 in packages/vue-query/tsconfig.prod.json
- packages/vue-query/src/__tests__/useQuery.test-d.ts#L106 in packages/vue-query/tsconfig.prod.json

Andarist added 3 commits July 20, 2025 08:51

Combine inferences from distributive conditional types

09e5824

keep those inferences when "external" candidates are found

cf7ea8a

fixup whitespace

ed80c21

Copilot AI review requested due to automatic review settings July 20, 2025 10:52

github-project-automation bot added this to PR Backlog Jul 20, 2025

github-project-automation bot moved this to Not started in PR Backlog Jul 20, 2025

typescript-bot added the For Backlog Bug PRs that fix a backlog bug label Jul 20, 2025

Copilot AI reviewed Jul 20, 2025

View reviewed changes

Andarist commented Jul 20, 2025

View reviewed changes

add extra test case

3a10dd2

Combine inferences from distributive conditional types #62093

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Combine inferences from distributive conditional types #62093

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tsc

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