If a function decl cannot be merged, mark it as invalid.

Clang currently crashes on

    class C {
      C() = default;
      C() = delete;
    };

My cunning plan for fixing this was to change the `if (!FnD)` in
Parser::ParseCXXInlineMethodDef() to `if (!FnD || FnD->isInvalidDecl)` – but
alas, the second constructor decl wasn't marked as invalid.  This lets
Sema::MergeFunctionDecl() return true on function redeclarations, which leads
to them being marked invalid.

This also improves error messages when functions are redeclared.

llvm-svn: 226365

clang/lib/Sema/SemaDecl.cpp

@@ -2761,6 +2761,7 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD,
             << New << New->getType();
         }
         Diag(OldLocation, PrevDiag) << Old << Old->getType();
+        return true;
 
       // Complain if this is an explicit declaration of a special
       // member that was initially declared implicitly.

clang/test/Parser/DelayedTemplateParsing.cpp

@@ -10,8 +10,8 @@ class A {
 
 template <class T>
 class B {
-   void foo4() { } // expected-note {{previous definition is here}}  expected-note {{previous definition is here}}
-   void foo4() { } // expected-error {{class member cannot be redeclared}} expected-error {{redefinition of 'foo4'}}
+   void foo4() { } // expected-note {{previous definition is here}}
+   void foo4() { } // expected-error {{class member cannot be redeclared}}
    void foo5() { } // expected-note {{previous definition is here}}
 
    friend void foo3() {

clang/test/Parser/cxx0x-ambig.cpp

@@ -110,8 +110,8 @@ namespace ellipsis {
   template<typename...T>
   struct S {
     void e(S::S());
-    void f(S(...args[sizeof(T)])); // expected-note {{here}}
-    void f(S(...args)[sizeof(T)]); // expected-error {{redeclared}} expected-note {{here}}
+    void f(S(...args[sizeof(T)])); // expected-note {{here}} expected-note {{here}}
+    void f(S(...args)[sizeof(T)]); // expected-error {{redeclared}}
     void f(S ...args[sizeof(T)]); // expected-error {{redeclared}}
     void g(S(...[sizeof(T)])); // expected-note {{here}} expected-warning {{ISO C++11 requires a parenthesized pack declaration to have a name}}
     void g(S(...)[sizeof(T)]); // expected-error {{function cannot return array type}}

clang/test/SemaCXX/class.cpp

@@ -119,9 +119,9 @@ struct C4 {
 // PR5415 - don't hang!
 struct S
 {
-  void f(); // expected-note 1 {{previous declaration}}
-  void S::f() {} // expected-error {{extra qualification on member}} expected-error {{class member cannot be redeclared}} expected-note {{previous declaration}} expected-note {{previous definition}}
-  void f() {} // expected-error {{class member cannot be redeclared}} expected-error {{redefinition}}
+  void f(); // expected-note 1 {{previous declaration}} expected-note {{previous declaration}}
+  void S::f() {} // expected-error {{extra qualification on member}} expected-error {{class member cannot be redeclared}}
+  void f() {} // expected-error {{class member cannot be redeclared}}
 };
 
 // Don't crash on this bogus code.

clang/test/SemaCXX/cxx1y-constexpr-not-const.cpp

@@ -11,8 +11,6 @@ struct X {
 
 // expected-error@6 {{class member cannot be redeclared}}
 // expected-note@5 {{previous}}
-// expected-error@6 {{non-constexpr declaration of 'f' follows constexpr declaration}}
-// expected-note@5 {{previous}}
 #else
 // expected-warning@5 {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const' to avoid a change in behavior}}
 #endif

clang/test/SemaCXX/cxx1y-deduced-return-type.cpp

@@ -21,8 +21,8 @@ int conv1c = conv1.operator auto();
 int conv1d = conv1.operator int(); // expected-error {{no member named 'operator int'}}
 
 struct Conv2 {
-  operator auto() { return 0; }  // expected-note 2{{previous}}
-  operator auto() { return 0.; } // expected-error {{cannot be redeclared}} expected-error {{redefinition of 'operator auto'}}
+  operator auto() { return 0; }  // expected-note {{previous}}
+  operator auto() { return 0.; } // expected-error {{cannot be redeclared}} expected-error {{cannot initialize return object of type 'auto' with an rvalue of type 'double'}}
 };
 
 struct Conv3 {

clang/test/SemaCXX/overload-decl.cpp

@@ -30,10 +30,8 @@ class X {
   static void g(int); // expected-error {{static and non-static member functions with the same parameter types cannot be overloaded}}
   static void g(float); // expected-error {{class member cannot be redeclared}}
 
-  void h(); // expected-note {{previous declaration is here}} \
-               expected-note {{previous declaration is here}}
-  void h() __restrict; // expected-error {{class member cannot be redeclared}} \
-                          expected-error {{conflicting types for 'h'}}
+  void h(); // expected-note {{previous declaration is here}}
+  void h() __restrict; // expected-error {{class member cannot be redeclared}}
 };
 
 int main() {} // expected-note {{previous definition is here}}