Fix "Union types are not being narrowed down correctly in 4.3 #44401" #44771
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I originally opened #44101 because it prevented a project of mine from compiling. I can confirm that this PR fixes the issue. I cloned this fork and could compile my project with the local compiler without touching my code in any way. Looking forward to having this merged, thank you so much @caojoshua!
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@ahejlsberg 👍/👎? |
src/compiler/checker.ts
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| @@ -18359,9 +18359,9 @@ namespace ts { | |||
| if (relation === comparableRelation && target.flags & TypeFlags.Primitive) { | |||
| const constraints = sameMap((source as IntersectionType).types, t => t.flags & TypeFlags.Primitive ? t : getBaseConstraintOfType(t) || unknownType); | |||
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I think the correct fix is to change this line to
| const constraints = sameMap((source as IntersectionType).types, t => t.flags & TypeFlags.Primitive ? t : getBaseConstraintOfType(t) || unknownType); | |
| const constraints = sameMap((source as IntersectionType).types, getBaseConstraintOrType); |
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Makes sense. Can confirm is passing the test. Just pushed this change.
| source = getIntersectionType(constraints); | ||
| if (!(source.flags & TypeFlags.Intersection)) { | ||
| return isRelatedTo(source, target, /*reportErrors*/ false); | ||
| const newSource = getIntersectionType(constraints); |
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These three lines should just be left unchanged. The intent is to overwrite the original intersection with the new and more specific intersection, and we rely on this substitution in the code the follows.
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Is there any chance that this will land in 4.4? |
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@KnorpelSenf yep, this will be in 4.4 (not in the Beta, which is already out, but any subsequent release) |
Fixes #44401
The regression occurred in this commit