Fix the parameter handling

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -419,6 +419,8 @@ Improvements to Clang's diagnostics
 - ``-Winitializer-overrides`` and ``-Wreorder-init-list`` are now grouped under
   the ``-Wc99-designator`` diagnostic group, as they also are about the
   behavior of the C99 feature as it was introduced into C++20. Fixes #GH47037
+- ``-Wreserved-identifier`` now fires on reserved parameter names in a function
+  declaration which is not a definition.
 
 Improvements to Clang's time-trace
 ----------------------------------

clang/lib/Sema/SemaDecl.cpp

@@ -10438,6 +10438,15 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   // Finally, we know we have the right number of parameters, install them.
   NewFD->setParams(Params);
 
+  // If this declarator is a declaration and not a definition, its parameters
+  // will not be pushed onto a scope chain. That means we will not issue any
+  // reserved identifier warnings for the declaration, but we will for the
+  // definition. Handle those here.
+  if (!Params.empty() && !D.isFunctionDefinition()) {
+    for (const ParmVarDecl *PVD : Params)
+      warnOnReservedIdentifier(PVD);
+  }
+
   if (D.getDeclSpec().isNoreturnSpecified())
     NewFD->addAttr(
         C11NoReturnAttr::Create(Context, D.getDeclSpec().getNoreturnSpecLoc()));
@@ -15333,7 +15342,6 @@ Decl *Sema::ActOnParamDeclarator(Scope *S, Declarator &D,
   if (D.isInvalidType())
     New->setInvalidDecl();
 
-  warnOnReservedIdentifier(New);
   CheckExplicitObjectParameter(*this, New, ExplicitThisLoc);
 
   assert(S->isFunctionPrototypeScope());