Reformatting everything now that we have `llvm` namespaces. I've
separated this from the main commit to help manage merge-conflicts and
for making it a bit easier to read the mega-patch.
This is phase-1 of switching from llvm::Optional to std::optional in the
next rebranch. llvm::Optional was removed from upstream LLVM, so we need
to migrate off rather soon. On Darwin, std::optional, and llvm::Optional
have the same layout, so we don't need to be as concerned about ABI
beyond the name mangling. `llvm::Optional` is only returned from one
function in
```
getStandardTypeSubst(StringRef TypeName,
bool allowConcurrencyManglings);
```
It's the return value, so it should not impact the mangling of the
function, and the layout is the same as `std::optional`, so it should be
mostly okay. This function doesn't appear to have users, and the ABI was
already broken 2 years ago for concurrency and no one seemed to notice
so this should be "okay".
I'm doing the migration incrementally so that folks working on main can
cherry-pick back to the release/5.9 branch. Once 5.9 is done and locked
away, then we can go through and finish the replacement. Since `None`
and `Optional` show up in contexts where they are not `llvm::None` and
`llvm::Optional`, I'm preparing the work now by going through and
removing the namespace unwrapping and making the `llvm` namespace
explicit. This should make it fairly mechanical to go through and
replace llvm::Optional with std::optional, and llvm::None with
std::nullopt. It's also a change that can be brought onto the
release/5.9 with minimal impact. This should be an NFC change.
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.
