Unnecessary parens could warn on `let foo = (bar);`

[alexcrichton]

Just another case that the unnecessary-parens lint could warn about. I don't think that the parens serve any use in that situation.

[milibopp]

I'll give it a try. I think this could be extended to operator assignments, too:

let mut foo = 0;
let bar = 1;
foo += (bar); // here

[huonw]

@aepsil0n sounds good: it should be possible to extend the match in rustc::middle::lint::check_unnecessary_parens to include ExprAssign and ExprAssignOp.

[pnkfelix]

I sometimes use "unnecessary" parens in order to compensate for my editor's (Emacs with rust-mode.el) auto-indent, e.g.:

    let a = if b { c }
        else { d };
    // versus
    let a = (if b { c }
             else { d });

Not sure whether I would just disable the unnecessary-parens lint in my projects, or if I would try to add an exception to the lint when the contained expression spans multiple lines in the source file.

[milibopp]

@pnkfelix Since there is no significant whitespace in Rust (unlike e.g. Python, where this totally makes sense), I'd intuitively say, that's an editor issue and not a syntax issue. Anyway, how would you check the expression for whether it's multiline?

[pnkfelix]

@aepsil0n You could check whether the expression crosses lines by using the expression's Span and CodeMap::lookup_char_pos , I think?

But as I tried to indicate, it could just be a matter of personal preference, and I can always disable the lint in my own projects.

[milibopp]

Yeah, I'll leave it out for now. Just being curious. ^^