Propagate expected type hints through struct literals. #40398
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eddyb
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beta-nominated
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r=me pending crater. |
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We discussed this in the @rust-lang/compiler meeting. It's a tough call regarding the backport. On the one hand, we definitely want to fix the bug, and it affects anybody using the Let's see what crater has to say (a clean run would help allay fears) before reaching a final decision. |
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Crater report only contains false positives (network errors, I think)! |
nikomatsakis
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S-waiting-on-crater
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OK, we're marking as beta-accepted. Live on the edge! cc @rust-lang/compiler |
nikomatsakis
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alexcrichton
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@bors r+ |
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📌 Commit 50aee36 has been approved by |
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Looks like this was never formally r+'d? |
frewsxcv
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Mar 17, 2017
Propagate expected type hints through struct literals. Partial fix for rust-lang#31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to. The added test works because `{...; x}` with a hint of `T` coerces `x` to `T`, and the reasoning why that is slightly different has to do with DSTs: `&Struct { tail: [x] }: &Struct<[T]>` has a hint of `[T]` for `[x]`, but the inferred type should be `[T; 1]` to succeed later, so `[x]` shouldn't be *forced* to be `[T]`. *However*, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes rust-lang#40355 and can be backported. r? @nikomatsakis
frewsxcv
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Mar 17, 2017
Propagate expected type hints through struct literals. Partial fix for rust-lang#31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to. The added test works because `{...; x}` with a hint of `T` coerces `x` to `T`, and the reasoning why that is slightly different has to do with DSTs: `&Struct { tail: [x] }: &Struct<[T]>` has a hint of `[T]` for `[x]`, but the inferred type should be `[T; 1]` to succeed later, so `[x]` shouldn't be *forced* to be `[T]`. *However*, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes rust-lang#40355 and can be backported. r? @nikomatsakis
frewsxcv
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Mar 18, 2017
Propagate expected type hints through struct literals. Partial fix for rust-lang#31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to. The added test works because `{...; x}` with a hint of `T` coerces `x` to `T`, and the reasoning why that is slightly different has to do with DSTs: `&Struct { tail: [x] }: &Struct<[T]>` has a hint of `[T]` for `[x]`, but the inferred type should be `[T; 1]` to succeed later, so `[x]` shouldn't be *forced* to be `[T]`. *However*, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes rust-lang#40355 and can be backported. r? @nikomatsakis
arielb1
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Mar 18, 2017
Propagate expected type hints through struct literals. Partial fix for rust-lang#31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to. The added test works because `{...; x}` with a hint of `T` coerces `x` to `T`, and the reasoning why that is slightly different has to do with DSTs: `&Struct { tail: [x] }: &Struct<[T]>` has a hint of `[T]` for `[x]`, but the inferred type should be `[T; 1]` to succeed later, so `[x]` shouldn't be *forced* to be `[T]`. *However*, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes rust-lang#40355 and can be backported. r? @nikomatsakis
frewsxcv
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Mar 20, 2017
Propagate expected type hints through struct literals. Partial fix for rust-lang#31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to. The added test works because `{...; x}` with a hint of `T` coerces `x` to `T`, and the reasoning why that is slightly different has to do with DSTs: `&Struct { tail: [x] }: &Struct<[T]>` has a hint of `[T]` for `[x]`, but the inferred type should be `[T; 1]` to succeed later, so `[x]` shouldn't be *forced* to be `[T]`. *However*, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes rust-lang#40355 and can be backported. r? @nikomatsakis
bors
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Mar 20, 2017
eddyb
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@nikomatsakis @brson If this made it into the stable release but wasn't merged on nightly, it might be missing from beta. I'll re-nominate it to make sure we don't forget to check (and backport if needed). |
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Partial fix for #31260 to maximize backwards-compatibility, i.e. the hint is provided but not coerced to.
The added test works because
{...; x}with a hint ofTcoercesxtoT, and the reasoning why that is slightly different has to do with DSTs:&Struct { tail: [x] }: &Struct<[T]>has a hint of[T]for[x], but the inferred type should be[T; 1]to succeed later, so[x]shouldn't be forced to be[T].However, implementing that complete behavior in a backwards-compatible way may be non-trivial, and has not yet been fully investigated, while this PR fixes #40355 and can be backported.
r? @nikomatsakis