Bonus points for recognizing idiomatic C-style for loops that could trivially be rewritten as for-in loops and providing a Fix-It to help with migration. For example:

for var x = 0; x != n; ++x { ... }

could be migrated to:

for x in 0..n { ... }

when x isn't written to.

I've been doing some diagnoses fixing recently and getting somewhat familiar with this area. Would be happy to take this on, if no one else has code in the works.

Still need to clean up the fix it ranges, but here's most of it: <https://github.com/apple/swift/pull/552\>.