test: Make a dedicated testsuite for rustfix

This commit adds a dedicated mode to compiletest for running rustfix tests,
adding a new `src/test/rustfix` directory which will execute all tests as a
"rustfix" test, namely requiring that a `*.fixed` is next to the main file which
is the result of the rustfix project's application of fixes.

The `rustfix` crate is pulled in to actually perform the fixing, and the rustfix
compiletest mode will assert a few properties about the fixing:

* The expected fixed output must be the same as rustc's output suggestions
  applied to the original code.
* The fixed code must compile successfully
* The fixed code must have no further diagnostics emitted about it

1 files changed, 15 insertions, 0 deletions

diff --git a/src/test/rustfix/tuple-float-index.fixed b/src/test/rustfix/tuple-float-index.fixed
new file mode 100644
index 00000000000..9cb7537b428
--- /dev/null
+++ b/src/test/rustfix/tuple-float-index.fixed
@@ -0,0 +1,15 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+fn main () {
+    ((1, (2, 3)).1).1;
+}