[ASTMatchers] Migrate away from ArrayRef(std::nullopt) (NFC)

[kazutakahirata]

ArrayRef has a constructor that accepts std::nullopt. This
constructor dates back to the days when we still had llvm::Optional.

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, I would like to move
away from the constructor and eventually remove it.

This patch migrates away from std::nullopt in favor of ArrayRef().
Note that {} would be ambiguous for perfect forwarding to work here.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Kazu Hirata (kazutakahirata)

Changes

ArrayRef has a constructor that accepts std::nullopt. This
constructor dates back to the days when we still had llvm::Optional.

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, I would like to move
away from the constructor and eventually remove it.

This patch migrates away from std::nullopt in favor of ArrayRef<T>().
Note that {} would be ambiguous for perfect forwarding to work here.

---

Full diff: https://github.com/llvm/llvm-project/pull/145840.diff

1 Files Affected:

• (modified) clang/lib/ASTMatchers/Dynamic/Marshallers.h (+1-1)

diff --git a/clang/lib/ASTMatchers/Dynamic/Marshallers.h b/clang/lib/ASTMatchers/Dynamic/Marshallers.h
index 0e640cbada726..d44e42a524f27 100644
--- a/clang/lib/ASTMatchers/Dynamic/Marshallers.h
+++ b/clang/lib/ASTMatchers/Dynamic/Marshallers.h
@@ -1060,7 +1060,7 @@ makeMatcherAutoMarshall(ReturnType (*Func)(), StringRef MatcherName) {
   BuildReturnTypeVector<ReturnType>::build(RetTypes);
   return std::make_unique<FixedArgCountMatcherDescriptor>(
       matcherMarshall0<ReturnType>, reinterpret_cast<void (*)()>(Func),
-      MatcherName, RetTypes, std::nullopt);
+      MatcherName, RetTypes, ArrayRef<ArgKind>());
 }
 
 /// 1-arg overload