Replace the use of bool and pointer returns for
`walkToXXXPre`/`walkToXXXPost`, and instead use
explicit actions such as `Action::Continue(E)`,
`Action::SkipChildren(E)`, and `Action::Stop()`.
There are also conditional variants, e.g
`Action::SkipChildrenIf`, `Action::VisitChildrenIf`,
and `Action::StopIf`.
There is still more work that can be done here, in
particular:
- SourceEntityWalker still needs to be migrated.
- Some uses of `return false` in pre-visitation
methods can likely now be replaced by
`Action::Stop`.
- We still use bool and pointer returns internally
within the ASTWalker traversal, which could likely
be improved.
But I'm leaving those as future work for now as
this patch is already large enough.
This allows us use an OptionSet parameter for
the request (as currently we can't directly use it
as a parameter due to not having an == definition
for it). It also allows us to regain default
arguments for the source loc and flag parameters.
Note that in all cases it was either nullptr or ctx.getLazyResolver().
While passing in nullptr might appear at first glance to mean something
("don't type check anything"), in practice we would check for a nullptr
value and pull out ctx.getLazyResolver() instead. Furthermore, with
the lazy resolver going away (at least for resolveDeclSignature() calls),
it won't make sense to do that anymore anyway.
The tool is currently hard-coded to find functions in the SwiftUI library that take parameters of type `(...) -> T` where `T: View` but where the parameter isn't annotated with `@ViewBuilder`. The long-term vision here, of course, is that this reads and interprets a script file, but that's quite a bit more work (especially to generate a million bindings to the AST). In the meantime, I think having a functional harness that people familiar with the C++ API can easily hack on to make their own tools is still pretty useful.
The harness does try to open a script file and lex the first token of it, because that's exactly as far as I got before deciding to hard-code the query I wanted. Since this input is otherwise ignored, you can just point the tool at any old `.swift` file (or just an empty file) and it'll be fine.
