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Fn traits with array args no longer work with const_generics enabled #67753

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Manishearth opened this issue Dec 31, 2019 · 9 comments · Fixed by #68312
Closed

Fn traits with array args no longer work with const_generics enabled #67753

Manishearth opened this issue Dec 31, 2019 · 9 comments · Fixed by #68312
Labels
A-const-generics Area: const generics (parameters and arguments) A-lazy-normalization Area: Lazy normalization (tracking issue: #60471) E-needs-test Call for participation: An issue has been fixed and does not reproduce, but no test has been added. F-const_generics `#![feature(const_generics)]` T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Manishearth
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#![feature(const_generics)]

fn main() {
    takes_closure_of_array_3(|[x, y, z]| {
        println!("args: x={}, y={}, z={}", x, y, z);
    });
}

fn takes_closure_of_array_3<F>(f: F)
where
    F: Fn([i32; 3]),
{
    f([1, 2, 3]);
}

(playpen)

Gives the error:

   Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/main.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default

error[E0391]: cycle detected when const-evaluating + checking `takes_closure_of_array_3::{{constant}}#0`
  --> src/main.rs:11:17
   |
11 |     F: Fn([i32; 3]),
   |                 ^
   |
note: ...which requires const-evaluating + checking `takes_closure_of_array_3::{{constant}}#0`...
  --> src/main.rs:11:17
   |
11 |     F: Fn([i32; 3]),
   |                 ^
......................
9  | / fn takes_closure_of_array_3<F>(f: F)
10 | | where
11 | |     F: Fn([i32; 3]),
12 | | {
13 | |     f([1, 2, 3]);
14 | | }
   | |_^

This compiles fine with const_generics not enabled, and is a regression

cc @Centril @oli-obk

@Manishearth Manishearth added the A-const-generics Area: const generics (parameters and arguments) label Dec 31, 2019
@Manishearth
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(discovered by @jcoglan)

@jonas-schievink jonas-schievink added A-lazy-normalization Area: Lazy normalization (tracking issue: #60471) requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 31, 2019
@JohnTitor JohnTitor added the F-const_generics `#![feature(const_generics)]` label Dec 31, 2019
@Centril Centril added the regression-from-stable-to-nightly Performance or correctness regression from stable to nightly. label Dec 31, 2019
@Centril
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Centril commented Dec 31, 2019

cc @nikomatsakis @eddyb @varkor

Simplified:

#![feature(const_generics)]

fn main() {
    takes_closure_of_array(|_| {});
}

fn takes_closure_of_array<F>(f: F)
where
    F: FnOnce([i32; 0]),
{
    f([]);
}

@Centril Centril added I-nominated P-high High priority labels Dec 31, 2019
@jonas-schievink
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Isn't this expected fallout?

@varkor
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varkor commented Dec 31, 2019

This is an expected consequence of #66883.

@Manishearth
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Seems like #60471 is what's supposed to eventually fix this?

@pnkfelix
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pnkfelix commented Jan 2, 2020

triage: P-medium (nightly-only regression on feature that is known to have bugs)

@pnkfelix pnkfelix added the P-medium Medium priority label Jan 2, 2020
@eddyb
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eddyb commented Jan 16, 2020

@varkor @oli-obk I think we've discussed this before, but what do you think of special-casing literals, to unblock at least some common usecases like this?

@oli-obk
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oli-obk commented Jan 17, 2020

I can't reproduce on master, this may have gotten fixed? (Note that the playground is severely outdated, a fix is underway for that though)

@varkor varkor added the E-needs-test Call for participation: An issue has been fixed and does not reproduce, but no test has been added. label Jan 17, 2020
@varkor
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varkor commented Jan 17, 2020

@eddyb pointed out that #68118 most likely fixed this.

@oli-obk oli-obk removed P-medium Medium priority regression-from-stable-to-nightly Performance or correctness regression from stable to nightly. requires-nightly This issue requires a nightly compiler in some way. labels Jan 17, 2020
tmandry added a commit to tmandry/rust that referenced this issue Jan 17, 2020
…ntril

Add regression test for integer literals in generic arguments in where clauses

Closes rust-lang#67753.
tmandry added a commit to tmandry/rust that referenced this issue Jan 18, 2020
…ntril

Add regression test for integer literals in generic arguments in where clauses

Closes rust-lang#67753.
@bors bors closed this as completed in 9d9c8c6 Jan 18, 2020
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Labels
A-const-generics Area: const generics (parameters and arguments) A-lazy-normalization Area: Lazy normalization (tracking issue: #60471) E-needs-test Call for participation: An issue has been fixed and does not reproduce, but no test has been added. F-const_generics `#![feature(const_generics)]` T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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8 participants