Migrate llvm::Optional to std::optional

[bnbarham]

LLVM has removed llvm::Optional, move over to std::optional. Also clang-format to fix up all the renamed #includes.

[bnbarham]

@swift-ci please test

[compnerd]

Seems pretty mechanical. Thank you for clang-formatting the patch!

[bnbarham]

@swift-ci please test

[bnbarham]

@swift-ci please test

[al45tair]

(On Windows) looks like maybe a missing #include <optional> somewhere:

C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\include\swift/Basic/Lazy.h(36,3): error: no template named 'optional' in namespace 'std'; did you mean 'llvm::Optional'?
   36 |   std::optional<T> Value;
      |   ^~~~~~~~~~~~~
      |   llvm::Optional
C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\stdlib\include\llvm/ADT/Optional.h(251,29): note: 'llvm::Optional' declared here
  251 | template <typename T> class Optional {
      |                             ^
1 error generated.
[107/308][ 34%][6.689s] Building CXX object stdlib\public\CMakeFiles\swiftDemangling-windows-x86_64.dir\__\__\lib\Demangling\Demangler.cpp.obj
[108/308][ 35%][6.792s] Building CXX object stdlib\public\runtime\CMakeFiles\swiftRuntime-windows-x86_64.dir\GenericMetadataBuilder.cpp.obj
In file included from C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\stdlib\public\runtime\GenericMetadataBuilder.cpp:17:
C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\include\swift/Runtime/GenericMetadataBuilder.h(400,11): warning: unused variable 'pattern' [-Wunused-variable]
  400 |     auto *pattern = patternBuffer.ptr;
      |           ^~~~~~~
C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\swift\stdlib\public\runtime\GenericMetadataBuilder.cpp(296,25): note: in instantiation of member function 'swift::GenericMetadataBuilder<InProcessReaderWriter>::buildGenericValueMetadata' requested here
  296 |   auto result = builder.buildGenericValueMetadata({description}, arguments,
      |                         ^
1 warning generated.

[al45tair]

Looks pretty mechanical. I've skimmed over most of it, but what I looked at all seemed good. There's a Windows issue, but that looks like a missing <optional> somewhere (probably some difference in the C++ library that causes it to be pulled in on the other platforms but not on the version we're using on Windows).

I'll be especially pleased to see the back of llvm::None as that causes problems adding None cases to enums.

[mikeash]

That's a big ol' diff. I didn't read it all, but assuming it's all s/llvm::Optional/std::optional/ then I'm happy.

[bnbarham]

Looks pretty mechanical. I've skimmed over most of it, but what I looked at all seemed good. There's a Windows issue, but that looks like a missing somewhere (probably some difference in the C++ library that causes it to be pulled in on the other platforms but not on the version we're using on Windows).

Yeah, MSVC doesn't end up pulling in <optional> from <functional> like macOS does (I didn't check where it's pulled in on Linux). I can easily fix this by adding <optional> into Basic/Lazy.h but I find it strange that the stdlib uses Basic at all TBH - I certainly wouldn't expect a Basic change to possibly impact ABI (and no, I don't know if we are using it in ABI somewhere, it just makes it very easy to).

I'll be especially pleased to see the back of llvm::None as that causes problems adding None cases to enums.

Heh. So just to be clear - this still doesn't remove it from a bunch of directories, namely ABI/Demangling/Remote*/Threading. These end up being used from the stdlib (and maybe ABI somewhere) as well as from tools. Technically those are all currently using std::optional though since that's what llvm::Optional is aliased to on main.

That's a big ol' diff. I didn't read it all, but assuming it's all s/llvm::Optional/std::optional/ then I'm happy.

If only. Unfortunately:

1. More Optional were added with a using namespace llvm
2. SourceKit and unittests both had the unqualified versions still
3. There's also None and NoneType

But... close enough :)

[xedin]

Went through most of the Sema.

[bnbarham]

swiftlang/llvm-project#8120

@swift-ci please test

[bnbarham]

swiftlang/llvm-project#8120

@swift-ci please test

[bnbarham]

swiftlang/llvm-project#8120

@swift-ci please test

[bnbarham]

swiftlang/llvm-project#8120

@swift-ci please test

[bnbarham]

swiftlang/llvm-project#8120

@swift-ci please test

[bnbarham]

@swift-ci please test

[bnbarham]

@swift-ci please test

[bnbarham]

@swift-ci please smoke test

[bnbarham]

@swift-ci please test Windows platform