[clang] Add scoped enum support to `StreamingDiagnostic` (#138089)

This patch adds templated `operator<<` for diagnostics that pass scoped
enums, saving people from `llvm::to_underlying()` clutter on the side of
emitting the diagnostic. This eliminates 80 out of 220 usages of
`llvm::to_underlying()` in Clang.

I also backported `std::is_scoped_enum_v` from C++23.

1 files changed, 3 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index b77cbdb..890df09 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -1670,24 +1670,21 @@ Sema::AccessResult Sema::CheckConstructorAccess(SourceLocation UseLoc,
   case InitializedEntity::EK_Base:
     PD = PDiag(diag::err_access_base_ctor);
     PD << Entity.isInheritedVirtualBase()
-       << Entity.getBaseSpecifier()->getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+       << Entity.getBaseSpecifier()->getType() << getSpecialMember(Constructor);
     break;
 
   case InitializedEntity::EK_Member:
   case InitializedEntity::EK_ParenAggInitMember: {
     const FieldDecl *Field = cast<FieldDecl>(Entity.getDecl());
     PD = PDiag(diag::err_access_field_ctor);
-    PD << Field->getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+    PD << Field->getType() << getSpecialMember(Constructor);
     break;
   }
 
   case InitializedEntity::EK_LambdaCapture: {
     StringRef VarName = Entity.getCapturedVarName();
     PD = PDiag(diag::err_access_lambda_capture);
-    PD << VarName << Entity.getType()
-       << llvm::to_underlying(getSpecialMember(Constructor));
+    PD << VarName << Entity.getType() << getSpecialMember(Constructor);
     break;
   }