Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add long explanation for E0757 #87342

Merged
merged 3 commits into from
Jul 21, 2021
Merged
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion compiler/rustc_error_codes/src/error_codes.rs
Original file line number Diff line number Diff line change
@@ -449,6 +449,7 @@ E0753: include_str!("./error_codes/E0753.md"),
E0754: include_str!("./error_codes/E0754.md"),
E0755: include_str!("./error_codes/E0755.md"),
E0756: include_str!("./error_codes/E0756.md"),
E0757: include_str!("./error_codes/E0757.md"),
E0758: include_str!("./error_codes/E0758.md"),
E0759: include_str!("./error_codes/E0759.md"),
E0760: include_str!("./error_codes/E0760.md"),
@@ -638,6 +639,5 @@ E0783: include_str!("./error_codes/E0783.md"),
// E0723, unstable feature in `const` context
E0726, // non-explicit (not `'_`) elided lifetime in unsupported position
// E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
E0757, // `#[ffi_const]` functions cannot be `#[ffi_pure]`
E0772, // `'static' obligation coming from `impl dyn Trait {}` or `impl Foo for dyn Bar {}`.
}
33 changes: 33 additions & 0 deletions compiler/rustc_error_codes/src/error_codes/E0757.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
A function was given both the `ffi_const` and `ffi_pure` attributes.

Erroneous code example:

```compile_fail,E0757
#![feature(ffi_const, ffi_pure)]

extern "C" {
#[ffi_const]
#[ffi_pure] // error: `#[ffi_const]` function cannot be `#[ffi_pure]`
pub fn square(num: i32) -> i32;
}
```

As `ffi_const` provides stronger guarantees than `ffi_pure`, remove the
`ffi_pure` attribute:

```
#![feature(ffi_const)]

extern "C" {
#[ffi_const]
pub fn square(num: i32) -> i32;
}
```

You can get more information about `const` and `pure` in the [GCC documentation
on Common Function Attributes]. The unstable Rust Book has more information
about [`ffi_const`] and [`ffi_pure`].

[GCC documentation on Common Function Attributes]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
[`ffi_const`]: https://doc.rust-lang.org/nightly/unstable-book/language-features/ffi-const.html
[`ffi_pure`]: https://doc.rust-lang.org/nightly/unstable-book/language-features/ffi-pure.html
1 change: 1 addition & 0 deletions src/test/ui/ffi_const2.stderr
Original file line number Diff line number Diff line change
@@ -6,3 +6,4 @@ LL | #[ffi_pure]

error: aborting due to previous error

For more information about this error, try `rustc --explain E0757`.