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]

rust/src/libsyntax/parse/parser.rs

Line 5386 in 9649c1f

fn parse_fn_args(&mut self, named_args: bool, allow_variadic: bool)

should have a call on the first argument to

rust/src/libsyntax/parse/parser.rs

Line 5463 in 9649c1f

fn parse_self_arg(&mut self) -> PResult<'a, Option<Arg>> {

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

You can look at

rust/src/libsyntax/parse/parser.rs

Line 5567 in 9649c1f

fn parse_fn_decl_with_self<F>(&mut self, parse_arg_fn: F) -> PResult<'a, P<FnDecl>>

to see how trait fns parse arguments.

You can see how a diagnostic is created here

rust/src/libsyntax/parse/parser.rs

Lines 803 to 821 in 9649c1f

	fn expected_ident_found(&self) -> DiagnosticBuilder<'a> {
	let mut err = self.struct_span_err(self.span,
	&format!("expected identifier, found {}",
	self.this_token_descr()));
	if let Some(token_descr) = self.token_descr() {
	err.span_label(self.span, format!("expected identifier, found {}", token_descr));
	} else {
	err.span_label(self.span, "expected identifier");
	if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
	err.span_suggestion_with_applicability(
	self.span,
	"remove this comma",
	String::new(),
	Applicability::MachineApplicable,
	);
	}
	}
	err
	}

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 👍 will do