emacs rust-mode: Cannot indent second line of a struct instantiation in some cases

[mwillsey]

Example:

Foo {a: 1, b: 2, c: 3,
d: 4, e: 5}

if you indent the second line, it will work and result in:

Foo {a: 1, b: 2, c: 3,
     d: 4, e: 5}

However, if there were a space after the '{':

Foo { a: 1, b: 2, c: 3,
d: 4, e: 5}

you would expect pressing tab on the second line to indent to:

Foo { a: 1, b: 2, c: 3,
      d: 4, e: 5}

instead an error is raised, saying that forward-to-word's definition is void.

[huonw]

cc #8793 and #8787

[johnwalker]

I just figured this out and am submitting a pull request for the fix.