Rollup merge of #76489 - GuillaumeGomez:add-explanation-e0756, r=jyn514
Add explanation for E0756 r? @pickfire
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ef6c3a7bca
@ -441,6 +441,7 @@
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E0753: include_str!("./error_codes/E0753.md"),
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E0754: include_str!("./error_codes/E0754.md"),
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E0755: include_str!("./error_codes/E0755.md"),
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E0756: include_str!("./error_codes/E0756.md"),
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E0758: include_str!("./error_codes/E0758.md"),
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E0759: include_str!("./error_codes/E0759.md"),
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E0760: include_str!("./error_codes/E0760.md"),
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@ -633,7 +634,6 @@
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E0722, // Malformed `#[optimize]` attribute
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E0726, // non-explicit (not `'_`) elided lifetime in unsupported position
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// E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
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E0756, // `#[ffi_const]` is only allowed on foreign functions
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E0757, // `#[ffi_const]` functions cannot be `#[ffi_pure]`
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E0772, // `'static' obligation coming from `impl dyn Trait {}` or `impl Foo for dyn Bar {}`.
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}
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29
compiler/rustc_error_codes/src/error_codes/E0756.md
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29
compiler/rustc_error_codes/src/error_codes/E0756.md
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@ -0,0 +1,29 @@
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The `ffi_const` attribute was used on something other than a foreign function
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declaration.
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Erroneous code example:
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```compile_fail,E0756
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#![feature(ffi_const)]
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#[ffi_const] // error!
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pub fn foo() {}
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# fn main() {}
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```
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The `ffi_const` attribute can only be used on foreign function declarations
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which have no side effects except for their return value:
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```
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#![feature(ffi_const)]
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extern "C" {
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#[ffi_const] // ok!
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pub fn strlen(s: *const i8) -> i32;
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}
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# fn main() {}
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```
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You can get more information about it in the [unstable Rust Book].
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[unstable Rust Book]: https://doc.rust-lang.org/nightly/unstable-book/language-features/ffi-const.html
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@ -6,3 +6,4 @@ LL | #[ffi_const]
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0756`.
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