Auto merge of #50084 - killercup:compiletest-rustfix, r=Manishearth

First step towards rustfix compiletest mode

This is the first small step towards testing auto-fixable compiler
suggestions using compiletest. Currently, it only checks if next to a
UI test there also happens to a `*.rs.fixed` file, and then uses rustfix
(added as external crate) on the original file, and asserts that it
produces the fixed version.

To show that this works, I've included one such test. I picked this test
case at random (and because it was simple) -- It is not relevant to the
2018 edition. Indeed, in the near future, we want to be able to restrict
rustfix to edition-lints, so this test cast might go away soon.

In case you still think this is somewhat feature-complete, here's a
quick list of things currently missing that I want to add before telling
people they can use this:

- [x] Make this an actual compiletest mode, with `test [fix] …` output
  and everything
- [x] Assert that fixed files still compile
- [x] Assert that fixed files produce no (or a known set of) diagnostics
  output
- [x] Update `update-references.sh` to support rustfix
- [x] Use a published version of rustfix (i.e.: publish a new version
  rustfix that exposes a useful API for this)

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;
+}