diag: methods sharing names with struct fields produce confusing diagnostic message

[bqwstt]

Unsure if this is a diagnostic or IR issue.

When lowering calls, we are not handling callable items that share names with identifiers. For example, struct methods called the same as one of their fields get treated as identifiers, thus lowering fails.

To me, this looks like an IR issue, but following the Language Guide, this may well be expected. If this is intentional, we should improve the error diagnostic to mention these name collisions (which can be confusing).

Example (playground example below):

struct A {
    field: u32,
}

impl A {
    fn field(self: &A) -> u32 {
        self.field
    }
}

fn main() {
    let a = A { field: 42 };
    println!("a.field={}", a.field());
}

Output:

error: function or static expected
  --> [program.alu:13:28](https://play.alumina-lang.net/#)

This happens in ir/mono/mod.rs's lower_call:

alumina/src/alumina-boot/src/ir/mono/mod.rs

Lines 5067 to 5093 in 304bf3f

	let (arg_types, return_type, callee) = match callee.ty {
	ir::Ty::FunctionPointer(arg_types, return_type) => (*arg_types, *return_type, callee),
	ir::Ty::Item(item) => match item.get().with_backtrace(&self.diag)? {
	ir::Item::Closure(closure) => {
	self_arg = Some(self.r#ref(callee, callee.span));
	let fun_item = closure.function.get().unwrap();
	let fun = fun_item.get_function().with_backtrace(&self.diag)?;
	fn_arg_types = fun.args.iter().skip(1).map(|p| p.ty).collect();
	(
	&fn_arg_types[..],
	fun.return_type,
	self.exprs.function(fun_item, callee.span),
	)
	}
	ir::Item::Function(fun) => {
	if fun.varargs {
	varargs = true;
	}
	fn_arg_types = fun.args.iter().map(|p| p.ty).collect();
	(&fn_arg_types[..], fun.return_type, callee)
	}
	_ => {
	bail!(self, CodeDiagnostic::FunctionOrStaticExpectedHere);
	}

Reproducible Example

https://play.alumina-lang.net/?code=1695451deb28b0f0

The above is a rather silly example (could just use field directly), but similar situations may happen (e.g., with a builder struct).

Compilation Info

Revision: 304bf3f4ff1f77739f31f3f7fe8c88c0f5b9e9fb

304bf3f4 (HEAD -> master, origin/master, origin/HEAD) chore: Add settings for Github Linguist (#117)

[tibordp]

Fields have precedence over methods in name resolution, so from the behavior perspective, this is expected, but I agree that it deserves a better error message.

Check out #119 for an improvement.

[bqwstt]

That was quick! Thanks, it's much more clear now.