PR47176: Don't read from an inactive union member if a friend function

has default arguments and an exception specification.

Author: zygoloid

clang/include/clang/Parse/Parser.h

@@ -1367,7 +1367,7 @@ class Parser : public CodeCompletionHandler {
 
     void ParseLexedMethodDeclarations() override;
 
-    Parser* Self;
+    Parser *Self;
 
     /// Method - The method declaration.
     Decl *Method;

clang/lib/Parse/ParseDecl.cpp

@@ -6486,6 +6486,10 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
       InitCXXThisScopeForDeclaratorIfRelevant(D, DS, ThisScope);
 
       // Parse exception-specification[opt].
+      // FIXME: Per [class.mem]p6, all exception-specifications at class scope
+      // should be delayed, including those for non-members (eg, friend
+      // declarations). But only applying this to member declarations is
+      // consistent with what other implementations do.
       bool Delayed = D.isFirstDeclarationOfMember() &&
                      D.isFunctionDeclaratorAFunctionDeclaration();
       if (Delayed && Actions.isLibstdcxxEagerExceptionSpecHack(D) &&

clang/lib/Parse/ParseDeclCXX.cpp

@@ -2186,17 +2186,20 @@ void Parser::HandleMemberFunctionDeclDelays(Declarator& DeclaratorInfo,
     auto LateMethod = new LateParsedMethodDeclaration(this, ThisDecl);
     getCurrentClass().LateParsedDeclarations.push_back(LateMethod);
 
-    // Stash the exception-specification tokens in the late-pased method.
-    LateMethod->ExceptionSpecTokens = FTI.ExceptionSpecTokens;
-    FTI.ExceptionSpecTokens = nullptr;
-
-    // Push tokens for each parameter.  Those that do not have
-    // defaults will be NULL.
+    // Push tokens for each parameter. Those that do not have defaults will be
+    // NULL. We need to track all the parameters so that we can push them into
+    // scope for later parameters and perhaps for the exception specification.
     LateMethod->DefaultArgs.reserve(FTI.NumParams);
     for (unsigned ParamIdx = 0; ParamIdx < FTI.NumParams; ++ParamIdx)
       LateMethod->DefaultArgs.push_back(LateParsedDefaultArgument(
           FTI.Params[ParamIdx].Param,
           std::move(FTI.Params[ParamIdx].DefaultArgTokens)));
+
+    // Stash the exception-specification tokens in the late-pased method.
+    if (FTI.getExceptionSpecType() == EST_Unparsed) {
+      LateMethod->ExceptionSpecTokens = FTI.ExceptionSpecTokens;
+      FTI.ExceptionSpecTokens = nullptr;
+    }
   }
 }
 

clang/test/Parser/cxx0x-decl.cpp

@@ -199,6 +199,11 @@ namespace AliasDeclEndLocation {
   B something_else;
 }
 
+class PR47176 {
+  friend void f(PR47176, int = 0) noexcept(true) {}
+};
+static_assert(noexcept(f(PR47176())), "");
+
 struct Base { virtual void f() = 0; virtual void g() = 0; virtual void h() = 0; };
 struct MemberComponentOrder : Base {
   void f() override __asm__("foobar") __attribute__(( )) {}