by value closure's span starts at `||` instead of at `move`

[oli-obk]

The related piece of code is

// libsyntax/parse/parser.rs:2104
                if try!(self.eat_keyword(keywords::Move) ){
                    return self.parse_lambda_expr(CaptureByValue);
                }

Since move got eaten, self.span.lo will point behind the move

// libsyntax/parse/parser.rs:2864
    pub fn parse_lambda_expr(&mut self, capture_clause: CaptureClause)
                             -> PResult<P<Expr>>
    {
        let lo = self.span.lo;

I don't know anything about the code in libsyntax. I'd probably make a mess of it.
My intuition says simply adding self.span.lo = lo; just before the return self.parse_lambda_expr(CaptureByValue); might not be the best idea, since other code might depend on lo not getting modified here.

[bombless]

I have a feeling that we don't have good regression test to see if codemap works correctly.
I hope it would help if we add some unit tests to libsyntax.

[oli-obk]

I guess one could use rustfmt as a regression test :D

Testing this indirectly is not too hard. One needs to find a diagnostic that uses a closure's span and then test that that diagnostic spans the closure correctly by breaking up the code by tokens into multiple lines.

move
||
{
// ...
}