Avoid silentNeverType leaking into generator types inferred based on inner generic calls at yields
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…n inner generic calls at `yield`s
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For Uncommitted Bug
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Pull Request Overview
This PR fixes an issue where silentNeverType was incorrectly leaking into generator types when inferring types based on inner generic calls at yield expressions. The change improves type inference for generators that use yield* with generic function calls by preventing premature type narrowing to never.
Key changes:
- Removes special handling of
silentNeverTypein yield expression type checking - Modifies check mode for yield expressions to skip generic function checks
- Updates test baselines to reflect improved type inference from
nevertoany
Reviewed Changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
| src/compiler/checker.ts | Core fix removing silentNeverType handling and adjusting check modes |
| tests/cases/compiler/genericCallAtYieldExpressionInGenericCall1.ts | Additional test cases for the fix |
| tests/baselines/reference/*.types | Updated type baselines showing improved inference |
| tests/baselines/reference/*.errors.txt | New error baselines for test cases |
| tests/baselines/reference/*.symbols | Symbol baselines for new test cases |
Andarist
commented
Aug 13, 2025
| @@ -39208,7 +39207,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker { | |||
| const nextTypes: Type[] = []; | |||
| const isAsync = (getFunctionFlags(func) & FunctionFlags.Async) !== 0; | |||
| forEachYieldExpression(func.body as Block, yieldExpression => { | |||
| const yieldExpressionType = yieldExpression.expression ? checkExpression(yieldExpression.expression, checkMode) : undefinedWideningType; | |||
| const yieldExpressionType = yieldExpression.expression ? checkExpression(yieldExpression.expression, checkMode && checkMode & ~CheckMode.SkipGenericFunctions) : undefinedWideningType; | |||
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this is exactly what the cousin (checkAndAggregateReturnExpressionTypes) of this function (checkAndAggregateYieldOperandTypes) does
Andarist
commented
Aug 13, 2025
| @@ -47,8 +47,8 @@ outer(function* <T>(value: T) { | |||
| > : ^^^^ | |||
| >outer : <A>(body: (value: A) => Generator<any, any, any>) => void | |||
| > : ^ ^^ ^^ ^^^^^ | |||
| >function* <T>(value: T) { const result = yield* inner(value); // ok} : <T>(value: T) => Generator<never, void, never> | |||
| > : ^ ^^ ^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |||
| >function* <T>(value: T) { const result = yield* inner(value); // ok} : <T>(value: T) => Generator<any, void, any> | |||
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the new results here are better and match the other results that have inner~ function called beforehand (when its precomputed result is yield*ed)
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@typescript-bot test it |
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Hey @jakebailey, the results of running the DT tests are ready. Everything looks the same! |
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@jakebailey Here are the results of running the user tests with tsc comparing There were infrastructure failures potentially unrelated to your change:
Otherwise... Everything looks good! |
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@jakebailey Here they are:
tscComparison Report - baseline..pr
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@jakebailey Here are the results of running the top 400 repos with tsc comparing Everything looks good! |
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This is an improvement over one of the recent PRs: #61317