Fixes microsoft#62737 When assigning objects with wider discriminator unions to discriminated union types, TypeScript now identifies the actual incompatible types from the source union, rather than showing a misleading error about a compatible type. Before: Type '"foo"' is not assignable to type '"bar"' After: The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target. This change: - Adds detection for discriminated union assignment errors - Reports which specific types from the source are missing in the target - Includes the discriminator property name in the error message - Adds comprehensive test cases

Improve error messages for discriminated union incompatible members#62837alpha2420 wants to merge 5 commits intomicrosoft:mainmicrosoft/TypeScript:mainfrom alpha2420:mainalpha2420/TypeScript:mainCopy head branch name to clipboard

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Commits on Dec 4, 2025

Improve error messages for discriminated union incompatible members

Fix formatting

Merge branch 'main' into main

Commits on Dec 5, 2025

Merge branch 'main' into main

fix: format forEachType callback as single line to pass dprint check

Improve error messages for discriminated union incompatible members#62837
alpha2420 wants to merge 5 commits intomicrosoft:mainfrom
alpha2420:main