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Wonky diagnostics on unsatisfied implicit Sized bounds #120178

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Flying-Toast opened this issue Jan 20, 2024 · 1 comment · Fixed by #120323
Closed

Wonky diagnostics on unsatisfied implicit Sized bounds #120178

Flying-Toast opened this issue Jan 20, 2024 · 1 comment · Fixed by #120323
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@estebank
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A-diagnostics Area: Messages for errors, warnings, and lints D-terse Diagnostics: An error or lint that doesn't give enough information about the problem at hand. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Flying-Toast
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Flying-Toast commented Jan 20, 2024 •
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Code

fn main() {
    let _ = std::mem::size_of::<[i32]>();
}

Current output

312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by this bound in `size_of`

The "this bound" doesn't actually point to a bound.

Desired output

Instead of "required by this bound"/"unsatisfied trait bound introduced here" we should say "note: T has an implicit bound of Sized"

Rationale and extra context

No response

Other cases

trait Foo {
    const VAL: usize;
}

impl<T> Foo for T {
    const VAL: usize = std::mem::size_of::<T>();
}

fn main() {
    println!("{}", <[i32] as Foo>::VAL);
}

Produces:

5  | impl<T> Foo for T {
   |      -  ^^^     ^
   |      |
   |      unsatisfied trait bound introduced here

Rust Version

rustc 1.75.0 (82e1608df 2023-12-21)
binary: rustc
commit-hash: 82e1608dfa6e0b5569232559e3d385fea5a93112
commit-date: 2023-12-21
host: x86_64-unknown-linux-gnu
release: 1.75.0
LLVM version: 17.0.6

Anything else?

No response
@Flying-Toast Flying-Toast added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 20, 2024
@Flying-Toast Flying-Toast changed the title Wonky diagnostic for size_of an unsized type Wonky diagnostics with auto trait bounds Jan 20, 2024
@fmease fmease changed the title Wonky diagnostics with auto trait bounds Wonky diagnostics on unsatisfied implicit Sized bounds Jan 21, 2024
@fmease
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fmease commented Jan 21, 2024

I've updated the title since Sized is not an auto trait and since this diagnostic issue is specific to Sized only.

@fmease fmease added the D-terse Diagnostics: An error or lint that doesn't give enough information about the problem at hand. label Jan 22, 2024
@estebank estebank self-assigned this Jan 24, 2024
estebank added a commit to estebank/rust that referenced this issue Jan 24, 2024
@estebank
On E0277 be clearer about implicit Sized bounds on type params and …
0421608 
…assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
@estebank estebank mentioned this issue Jan 24, 2024
Merged
estebank added a commit to estebank/rust that referenced this issue Jan 26, 2024
@estebank
On E0277 be clearer about implicit Sized bounds on type params and …
7ac2dea 
…assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
estebank added a commit to estebank/rust that referenced this issue Jan 30, 2024
@estebank
On E0277 be clearer about implicit Sized bounds on type params and …
2875d7e 
…assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
Nadrieril added a commit to Nadrieril/rust that referenced this issue Jan 31, 2024
@Nadrieril
Rollup merge of rust-lang#120323 - estebank:issue-120178, r=fmease
384a303 
On E0277 be clearer about implicit `Sized` bounds on type params and assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 1, 2024
@matthiaskrgr
Rollup merge of rust-lang#120323 - estebank:issue-120178, r=fmease
3f08692 
On E0277 be clearer about implicit `Sized` bounds on type params and assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 1, 2024
@matthiaskrgr
Rollup merge of rust-lang#120323 - estebank:issue-120178, r=fmease
3bfa58a 
On E0277 be clearer about implicit `Sized` bounds on type params and assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 4, 2024
@matthiaskrgr
Rollup merge of rust-lang#120323 - estebank:issue-120178, r=fmease
6af0458 
On E0277 be clearer about implicit `Sized` bounds on type params and assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
@bors bors closed this as completed in c4c22b0 Feb 5, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 5, 2024
@rust-timer
Unrolled build for rust-lang#120323
e890bd9 
Rollup merge of rust-lang#120323 - estebank:issue-120178, r=fmease

On E0277 be clearer about implicit `Sized` bounds on type params and assoc types

```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> f100.rs:2:33
    |
2   |     let _ = std::mem::size_of::<[i32]>();
    |                                 ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
   --> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
    |
312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by the implicit `Sized` requirement on this bound in `size_of`
```

Fix rust-lang#120178.
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A-diagnostics Area: Messages for errors, warnings, and lints D-terse Diagnostics: An error or lint that doesn't give enough information about the problem at hand. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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On E0277 be clearer about implicit Sized bounds on type params and assoc types estebank/rust
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@estebank @fmease @Flying-Toast