Support coercion between (FnDef | Closure) and (FnDef | Closure) #71599
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r? @cramertj (rust_highfive has picked a reviewer for you, use r? to override) |
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r? @eddyb |
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Hmm, so, let me double check my understanding here. The current rule for closures is:
But we are trying to extend that rule to permit coercions in other cases as well? (i.e., not just based on the expected type)? |
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@nikomatsakis Yes, that's currently how it works and what this PR is going to achieve. The Closure and FnDef are pretty similar and I think this extended rule respects the RFC 1558 (tracking issue: #39817). One thing I forget to add is the non-capturing closure restriction. I'm working on it. |
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Non-capturing closure restriction added. |
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Found this also fixes #48109, check-pass test added. |
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Side note that this PR reminded me that I think we ought to improve our diagnostics here, so I filed #71895. |
nikomatsakis
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May 4, 2020
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Nominating for discussion in the @rust-lang/lang meeting -- this PR is proposing an extension to our rules around closure capture and coercion. It is probably a good change, but I thought I would raise it so we can discuss briefly. |
nikomatsakis
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May 6, 2020
… Closure is non-capturing
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We discussed this in our rust-lang meeting and the consensus was that extending coercions for non-capturing closures to occur in other contexts was pretty reasonable. |
nikomatsakis
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May 11, 2020
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I guess this is more or less ready to land. I'm wondering whether we need to update the rust reference, but I guess its coverage of coercions is insufficiently detailed at the moment to really make that make sense. |
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@nikomatsakis I think we need it. So I filed a PR for it. rust-lang/reference#808. But sadly the RFC 401 seems to be ignoring the LUB coercion. So I haven't seen any regulation on it. |
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@ldm0 yeah, I don't think it was an RFC'd change. |
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@bors r+ |
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📌 Commit 42396b1 has been approved by |
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May 18, 2020
Support coercion between (FnDef | Closure) and (FnDef | Closure) Fixes rust-lang#46742, fixes rust-lang#48109 Inject `Closure` into the `FnDef x FnDef` coercion special case, which makes coercion of `(FnDef | Closure) x (FnDef | Closure)` possible, where closures should be **non-capturing**.
This was referenced May 18, 2020
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May 18, 2020
Rollup of 5 pull requests Successful merges: - rust-lang#71599 (Support coercion between (FnDef | Closure) and (FnDef | Closure)) - rust-lang#71973 (Lazy normalization of constants (Reprise)) - rust-lang#72283 (Drop Elaboration Elaboration) - rust-lang#72290 (Add newer rust versions to linker-plugin-lto.md) - rust-lang#72318 (Add help text for remote-test-client) Failed merges: r? @ghost
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Fixes #46742, fixes #48109
Inject
Closureinto theFnDef x FnDefcoercion special case, which makes coercion of(FnDef | Closure) x (FnDef | Closure)possible, where closures should be non-capturing.