A label range of 0 length was being reported as the label of trailing closure
arguments, just before the opening '{'.
For the rename refactoring, this meant that if the corresponding parameter had
an external label (e.g. 'a') the occurrence would be treated as not matching the
expected symbol name, and so not be updated at all.
For the migrator, when renaming a function with an unlabelled closure for its
last parameter to have a label, it would incorrectly insert the new label in
front of the opening '{' on all of that function's callsites with trailing
closures.
Resolves rdar://problem/42162571
This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.
Some of the implicit decls generated for lazy vars have invalid source ranges.
For now, just always walk into implicit decls when looking for name locations.
Resolves rdar://problem/35255644.
Adds support for renaming subscripts with external names, e.g.
subscript(x y: Int), and introduces a noncollapsible parameter name range for
subscript parameters, since these shouldn't be collapsed with an argument label
of the same name as function parameter names are.