add a compile error note for field name shadowing struct member function

[andrewrk]

const xxx = struct {
    bar: u8,
    pub fn bar(self: *const xxx) void {}
};

pub fn main() !void {
    var x: xxx = undefined;
    x.bar();
}

O:\zig0.1.1\b.zig:10:4: error: type 'u8' not a function
  x.bar();
   ^

[andrewrk]

I'm going to call this "working as designed". The function is not actually shadowed by the field. It can be referenced like this:

const xxx = struct {
    bar: u8,
    pub fn bar(self: *const xxx) void {}
};

test "non-member fn call" {
    var x: xxx = undefined;
    xxx.bar(&x);
}

However, the error message could be improved with a note that says "note: 'bar' is both a field and a top level declaration". That's a relatively low priority though.

If we had different syntax for field access and for method calls, this would not be an issue. I wonder how well-received it would be for method calls to be a->b().

[daurnimator]

What about when you take the address of a member?

const xxx = struct {
    bar: u8,
    pub fn bar(self: *const xxx) void {}
};

test "non-member fn call" {
    var x: xxx = undefined;
    var bar = &x.bar; // do I now have a function pointer? or a pointer to the member
    bar(x); // what about now?
}

[tgschultz]

Related: #1836