Servo has used this since forever, and it'd be useful to be able to use
rustfmt stable there so that we can use the same rustfmt version in
both Firefox and Servo.

Feel free to close this if there's any reason it shouldn't be done.

Closes rust-lang#3368

Previously, non-trivial type aliases in extern blocks were dropped by
rustfmt because only the type alias name would be passed to a rewritter.
This commit fixes that by passing all type information (generics,
bounds, and assignments) to a type alias rewritter, and consolidates
`rewrite_type_alias` and `rewrite_associated_type` as one function.

Closes rust-lang#4159

…#4166)

Previously the indetation of a line was compared with the configured
number of spaces per tab, which could cause lines that were formatted
with hard tabs not to be recognized as indented ("\t".len() < "    ".len()).

Closes rust-lang#4152

* Exclude code block delimiters when wrapping comments

Closes rust-lang#4158

* fixup! Exclude code block delimiters when wrapping comments

For an end user, the number of characters in a string is most likely
interpreted as the number of [grapheme cluster](http://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries)s in the string,
which may be different than either the number of unicode codepoints or
bytes. Use the number of graphemes to determine list comment alignment
rather than the byte length of the line.

Closes rust-lang#4151

I'm not sure there's a better way to do this without a larger refactor
of this method.

Closes rust-lang#4104

rustfmt tries to preserve the comment between a fn return type and the
start of the fn body if there are no where clauses following the return
type. However, even if there are no where clauses present, the "where"
keyword may be. To elide the "where" keyword in this context, just get
the comment snippet starting after the where clause span, which always
includes the "where" keyword if present.

Closes rust-lang#4001

Servo has used this since forever, and it'd be useful to be able to use
rustfmt stable there so that we can use the same rustfmt version in
both Firefox and Servo.

Feel free to close this if there's any reason it shouldn't be done.

Closes rust-lang#3380

* Preserve comments in empty statements

Closes rust-lang#4018

* fixup! Preserve comments in empty statements

…ving a struct's commas (rust-lang#4201)

…om/bradleypmartin/rustfmt into bradleypmartin-test-recursive-mode