Rust: Erroneous self arguments on bare functions emit subpar compilation error

[nox]

When refactoring methods as bare functions and forgetting to remove the self argument, the compiler fails to parse the new function entirely instead of emitting a better error.

error: expected one of `::` or `:`, found `,`
    --> components/canvas_traits/webgl.rs:1000:10
     |
1000 |     &self,
     |          ^ expected one of `::` or `:` here

[estebank]

https://github.com/rust-lang/rust/blob/9649c1f70fddd01843024932df97fb5a2b10bfe8/src/libsyntax/parse/parser.rs#L5386

should have a call on the first argument to

https://github.com/rust-lang/rust/blob/9649c1f70fddd01843024932df97fb5a2b10bfe8/src/libsyntax/parse/parser.rs#L5463

which if the result is Ok(Some(_)) a custom diagnostic should be raised pointing at the argument.

You can look at

https://github.com/rust-lang/rust/blob/9649c1f70fddd01843024932df97fb5a2b10bfe8/src/libsyntax/parse/parser.rs#L5567

to see how trait fns parse arguments.

You can see how a diagnostic is created here

https://github.com/rust-lang/rust/blob/9649c1f70fddd01843024932df97fb5a2b10bfe8/src/libsyntax/parse/parser.rs#L803-L821

and after that all that is needed for that error to be outputted is to call err.emit().

---

https://forge.rust-lang.org has information on the compiler itself, you'll want to at the very least look at https://forge.rust-lang.org/x-py.html.

[lcnr]

Hello, I would like to work on this

[lcnr]

As this is also causing the same error message, I think that it might actually be better to check for self in every argument position:

struct Foo {}

impl Foo {
    fn foo(a: u32, &mut self) {

    }
}

fn bar(a: u32, self) {}

playground

[estebank]

@Axary

As this is also causing the same error message

That is a good point. It's probably a good idea to have _different_ error message for the (so far) three cases. On Foo::foo, you should complain that self should appear first, if there are many that there should be one, in bar you should complain that self is only valid in trait fns.

[lcnr]

Ok :+1: will do