PR18275: If a member function of a class template is declared with a

const-qualified parameter type and the defined with a non-const-qualified
parameter type, the parameter is not const inside its body. Ensure that
the type we use when instantiating the body is the right one. Patch by
suyog sarda!

This is still rather unsatisfactory; it seems like it might be better to
instantiate at least the function parameters, and maybe the complete function
declaration, when we instantiate the definition for such a member function
(instead of reusing the declaration from inside the instantiated class
definition).

llvm-svn: 203741

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -2991,6 +2991,14 @@ static void addInstantiatedParametersToScope(Sema &S, FunctionDecl *Function,
       // Simple case: not a parameter pack.
       assert(FParamIdx < Function->getNumParams());
       ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
+      // If the parameter's type is not dependent, update it to match the type
+      // in the pattern. They can differ in top-level cv-qualifiers, and we want
+      // the pattern's type here. If the type is dependent, they can't differ,
+      // per core issue 1668.
+      // FIXME: Updating the type to work around this is at best fragile.
+      if (!PatternDecl->getType()->isDependentType())
+        FunctionParam->setType(PatternParam->getType());
+
       FunctionParam->setDeclName(PatternParam->getDeclName());
       Scope.InstantiatedLocal(PatternParam, FunctionParam);
       ++FParamIdx;
@@ -3005,6 +3013,9 @@ static void addInstantiatedParametersToScope(Sema &S, FunctionDecl *Function,
            "should only be called when all template arguments are known");
     for (unsigned Arg = 0; Arg < *NumArgumentsInExpansion; ++Arg) {
       ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
+      if (!PatternDecl->getType()->isDependentType())
+        FunctionParam->setType(PatternParam->getType());
+
       FunctionParam->setDeclName(PatternParam->getDeclName());
       Scope.InstantiatedLocalPackArg(PatternParam, FunctionParam);
       ++FParamIdx;

clang/test/SemaTemplate/dependent-type-identity.cpp

@@ -98,3 +98,27 @@ namespace PR7460 {
   template <typename T>
   T TemplateClass2<T>::member[TemplateClass2<T>::SIZE];
 }
+
+namespace PR18275 {
+  template<typename T> struct A {
+    void f(const int);
+    void g(int);
+    void h(const T);
+    void i(T);
+  };
+
+  template<typename T>
+  void A<T>::f(int x) { x = 0; }
+
+  template<typename T>
+  void A<T>::g(const int x) { x = 0; } // expected-error {{not assignable}}
+
+  template<typename T>
+  void A<T>::h(T) {} // FIXME: Should reject this. Type is different from prior decl if T is an array type.
+
+  template<typename T>
+  void A<T>::i(const T) {} // FIXME: Should reject this. Type is different from prior decl if T is an array type.
+
+  template struct A<int>;
+  template struct A<int[1]>;
+}