Recognize splices as parts of valid declaration specifiers.

Closes llvm#29.

Author: katzdm

clang/lib/Parse/ParseDecl.cpp

@@ -5862,12 +5862,15 @@ bool Parser::isDeclarationSpecifier(
     [[fallthrough]];
   case tok::kw_decltype: // decltype(T())::type
   case tok::kw_typename: // typename T::type
+  case tok::l_splice:
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.
     if (TryAnnotateTypeOrScopeToken(AllowImplicitTypename))
       return true;
     if (TryAnnotateTypeConstraint())
       return true;
+    if (Tok.is(tok::annot_splice))
+      return true;
     if (Tok.is(tok::identifier))
       return false;
 

clang/test/Reflection/splice-types.cpp

@@ -76,6 +76,10 @@ consteval auto decr(typename [:r_int:] p) -> [:r_const_int:] {
   return p - 1;
 }
 static_assert(decr(13) == 12);
+
+// 'typename' should be optional in parameter declarations.
+void fn([:r_int:]);
+class S { S([:r_int:]); };
 }  // in_fn_defs
 
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