When converting a call or function, rename declarations such that
redeclaration errors and shadowing are avoided. In some cases this will
be overly conservative, but since any renamed variable can be fixed with
edit all in scope, this is preferred over causing redeclaration errors
or possible shadowing.
Resolves rdar://73973517
Adds three refactorings intended to help users migrate their existing
code to use the new async language features:
1. Convert call to use async alternative
2. Convert function to async
3. Add async alternative function
A function is considered to have an async alternative if it has a void
return type and has a void returning closure as its last parameter. A
method to explicitly mark functions as having an async alternative may
be added to make this more accurate in the future (required for eg.
a warning about a call to the non-async version of a function in an
async context).
(1) converts a call to use the new `await` async language syntax. If the
async alternative throws, it will also add `try`. The closure itself is
hoisted out of the call, see the comments on
`AsyncConversionStringBuilder` for specifics.
(2) converts a whole function to `async`, using (1) to convert any calls
in the function to their async alternatives. (3) is similar to (2), but
instead *adds* a function and replaces calls to its
completion/handler/callback closure parameter with `return` or `throws`.
Resolves rdar://68254700
These were duplicated in 11 different files, and as they've gotten more
complex a few inconsistencies have snuck in. Sharing them should make future
changes easier and less bug-prone.
