E0495 documentation wrongly states it is no longer emitted by the compiler

[nodakai]

Location

https://doc.rust-lang.org/error_codes/E0495.html

Note: this error code is no longer emitted by the compiler.

Summary

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=0a915b8449387a0b5162ada85854dfa6

It is emitted by the latest stable 1.84.1 & nightly

[workingjubilee]

Nice catch!

[chenyukang]

E0495 now is emitted at here, https://github.com/chenyukang/rust/blob/a917fd5f98913a04b839cccca43558f4e4fc831b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs#L1032-L1038

the meaning of error seems changed, we need to update the document for E0495.

[xizheyin]

Could I help with update the doc?

[chenyukang]

Could I help with update the doc?

yeah, go ahead!

[xizheyin]

@rustbot claim

[workingjubilee]

Either the doc for the error code should be updated or another error code should be used and the diagnostics with the drifted meaning should be attached to this new error. I'm not attached to either particular course of action.

[progressive-galib]

#137042 documentation update done

[progressive-galib]

A trait implementation returns a reference without an explicit lifetime linking it to self`.

trait Tr<X> {
    fn f(&self) -> X;
}

struct Wr<'b> {
    ri: &'b i32,
    f: f32,
}

impl<'b> Tr<&f32> for Wr<'b> {
    fn f(&self) -> &f32 { // error: missing lifetime linking &f32 to self
        &self.f
    }
}

Specify an explicit lifetime in the trait to ensure that the reference returned is valid for at least as long as self:

trait Tr<'a, X> {
    fn f(&'a self) -> X;
}

struct Wr<'b> {
    ri: &'b i32,
    f: f32,
}

impl<'a, 'b: 'a> Tr<'a, &'a f32> for Wr<'b> {
    fn f(&'a self) -> &'a f32 { // ok!
        &self.f
    }
}

`

[progressive-galib]

E0495 now is emitted at here, https://github.com/chenyukang/rust/blob/a917fd5f98913a04b839cccca43558f4e4fc831b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs#L1032-L1038

the meaning of error seems changed, we need to update the document for E0495.

after reading this and doing some digging i think current error from
`trait Tr {
fn f(&self) -> X;
}

struct Wr<'b> {
ri: &'b i32,
f: f32,
}

impl<'b> Tr<&f32> for Wr<'b> {
fn f(&self) -> &f32 {
&self.f
}
}`

is very different from current E095, so we should create a new error and document his behavior there. that way we can preserve documentation for old versions of compiler and keep the documentation consistent.

[xizheyin]

Ok, I have alloced a new errorcode.