[ty] Preserve literal-string origin in comparison narrowing - #27582
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[ty] Preserve literal-string origin in comparison narrowing#27582carljm wants to merge 1 commit into
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 96.96%. The percentage of expected errors that received a diagnostic held steady at 92.96%. The number of fully passing files held steady at 106/133. |
Memory usage reportMemory usage unchanged ✅ |
|
| Lint rule | Added | Removed | Changed |
|---|---|---|---|
unsound-return-statement |
0 | 0 | 1 |
| Total | 0 | 0 | 1 |
Flaky changes detected. This PR summary excludes flaky changes; see the HTML report for details.
Raw diff:
meson (https://github.com/mesonbuild/meson)
- mesonbuild/compilers/mixins/visualstudio.py:392:16 warning[unsound-return-statement] Unsound return statement: `list[str] | list[str | Divergent]` is not a subtype of `list[str]`
+ mesonbuild/compilers/mixins/visualstudio.py:392:16 warning[unsound-return-statement] Unsound return statement: `list[str] | list[Divergent]` is not a subtype of `list[str]`
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Summary
This PR implements a consistent view of the semantics of
LiteralStringand stringLiteraltypes. The key observation is that ifLiteral["hello"] <: LiteralString <: strholds, andLiteralStringis not equivalent tostr, that necessarily implies thatLiteral["hello"]does not include all runtime string objects with the value"hello"-- only those that are known to have literal origin (that is, those that also inhabitLiteralString).Similar to
NewTypeand generic specializations, this can be described in terms of typed values having both a runtime object and possibly static-only "tags", which don't exist at runtime but still participate in determining which types they inhabit. So a runtime string object with value"hello"may be a typed value that carries the "literal origin" tag (in this case it inhabitsLiteralStringandLiteral["hello"]), or may not carry that tag (in which case it inhabits neitherLiteralStringnorLiteral["hello"].)This PR just carries this understanding consistently through our narrowing support.
LiteralStringorigin.Closes astral-sh/ty#4214.
Test plan
str & ~LiteralString,str & ~Literal["hello"], and~Literal["hello"]across comparison truthiness and equality/identity narrowing, including reversed operands, inequality branches, optional unions, and strict equality semantics.