[WIP] Implement DST coercions. #23785
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See #24619 for the rebased and finished off version. |
alexcrichton
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
alexcrichton
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
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…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 10, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 10, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
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Mar 11, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
arielb1
pushed a commit
to arielb1/rust
that referenced
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Mar 11, 2017
…r=nikomatsakis Disallow subtyping between T and U in T: Unsize<U>. Because `&mut T` can be coerced to `&mut U`, `T` and `U` must be unified invariantly. Fixes rust-lang#40288. E.g. coercing `&mut [&'a X; N]` to `&mut [&'b X]` must require `'a` be equal to `'b`, otherwise you can convert between `&'a X` and `&'b X` (in either direction), potentially unsoundly lengthening lifetimes. Subtyping here was introduced with `Unsize` in rust-lang#24619 (landed in 1.1, original PR is rust-lang#23785).
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This implements the new opt-in coercion mechanism from rust-lang/rfcs#982.
The first 7 commits are refactoring, then a partial fix for #23785,
Unsize,CoerceUnsized, intrinsics andRcsupport, each with its own commit.Only the last two actually affect stable APIs and they may be taken out to speed out merging the core changes (or just the refactoring).
TODO:
CoerceUnsized(errors related to region inference are somewhat different) and a couple of LLVM assertionsis_nullimplemented on pointers to unsized typesRcchanges forArcUnsizeandCoerceUnsized- there's so much to do here, I'm considering centralizing testing for DST, but then again...const-polymorphic-pathsused to be an experiment in DRY testing of many combinations and it ended up really weird, with all that macro abuse 😞r? @nikomatsakis or @nrc
f? @pcwalton