Missing "unnecessary parentheses" warning

[leonardo-m]

This program compiles without warnings:

fn main() {
    use std::ops::Range;
    fn foo(r1: Range<u32>, r2: Range<u32>) {
        for _ in r1 {}
        for _ in r2 {}
    }
    foo((0 .. 10), (0 .. 10)); // ***
    foo(0 .. 10, 0 .. 10);
}

I expected a "unnecessary parentheses" warning on the first call to foo() because #[warn(unused_parens)] is on by default.

[zackmdavis]

This is because we currently don't check for unused parens in call arguments:

rust/src/librustc_lint/unused.rs

Lines 294 to 306 in 1699293

	let (value, msg, struct_lit_needs_parens) = match e.node {
	If(ref cond, ..) => (cond, "`if` condition", true),
	While(ref cond, ..) => (cond, "`while` condition", true),
	IfLet(_, ref cond, ..) => (cond, "`if let` head expression", true),
	WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
	ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
	Match(ref head, _) => (head, "`match` head expression", true),
	Ret(Some(ref value)) => (value, "`return` value", false),
	Assign(_, ref value) => (value, "assigned value", false),
	AssignOp(.., ref value) => (value, "assigned value", false),
	InPlace(_, ref value) => (value, "emplacement value", false),
	_ => return,
	};

(notice: no ast::ExprKind::Call or ::MethodCall in the match).

So another example would be:

fn add_one(n: usize) -> usize {
    n + 1
}

fn main() {
    add_one((2));
}