Rust: Type inference for pattern matching #20020
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| class AccessPosition = DeclarationPosition; | ||
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| class Access extends StructPat { | ||
| Type getTypeArgument(TypeArgumentPosition apos, TypePath path) { none() } |
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Since #19847, getTypeArgument is only used for type arguments supplied to functions, not to their defining type, i.e. it is used for foo::<i32>(...) but not for Bar::<i32>::foo(...).
Since explicit type arguments in pattern matching corresponds to the latter, it is none() here, and instead handled in getInferredType below. I'll add some tests for this.
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Adding test, of course, revealed some corner cases that were not handled, I'm gonna do that on this PR as well.
| let x = value1; // $ MISSING: type=x:i32 | ||
| let y = value2; // $ MISSING: type=y:bool | ||
| let x = value1; // $ type=x:i32 | ||
| let y = value2; // $ type=y:bool | ||
| (); | ||
| } | ||
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| let my_tuple_struct = MyTupleStruct(42, false); | ||
| if let MyTupleStruct(value1, value2) = my_tuple_struct { |
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There are a bunch of other pattern types, lets add some tests for those too. No need to fully implement them all, having some MISSING annotations is fine.
Let's also add some more tests with:
- some more deeply nested patterns
- use of
refkeyword:let Some(ref x) = ... - a
uniontype
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Good idea with nested patterns and ref; we don't handle union types yet, so I'll not add those here.
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I just asked co-pilot to generate sample test code that covers all the cases for Pat from the ungrammar. This is the result hvitved#8 .
I had to drop the sample code about "const block patterns" because that feature has been removed from Rust.
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Could we perhaps add those tests follow-up?
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Sure, just wanted to let you know, so you wouldn't write them manually.
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I was thinking we could do that once we even support tuple types. |
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This PR implements type inference support for pattern matching. For example, we are now able to infer that
xhas typei32inWe also fix an existing bug where we would not distinguish
let x = ...fromlet ref x = ..., as well as handling type arguments supplied to variants, e.g.Option::Some::<i32>(Default::default)(#19847 follow-up).Commit-by-commit review is encouraged.
DCA looks great; call resolution rate up by 2.5 percentage points, no significant performance regressions.