Tweak the fix to PR8977: an empty expression-list represents value initialization, not default initialization. Fixes PR11712.

llvm-svn: 147620

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1172,6 +1172,8 @@ def err_auto_var_requires_init : Error<
   "declaration of variable %0 with type %1 requires an initializer">;
 def err_auto_new_requires_ctor_arg : Error<
   "new expression for type %0 requires a constructor argument">;
+def err_auto_var_init_no_expression : Error<
+  "initializer for variable %0 with type %1 is empty">;
 def err_auto_var_init_multiple_expressions : Error<
   "initializer for variable %0 with type %1 contains multiple expressions">;
 def err_auto_new_ctor_multiple_expressions : Error<

clang/lib/Sema/SemaDeclCXX.cpp

@@ -8898,8 +8898,6 @@ void Sema::AddCXXDirectInitializerToDecl(Decl *RealDecl,
                                          MultiExprArg Exprs,
                                          SourceLocation RParenLoc,
                                          bool TypeMayContainAuto) {
-  assert(Exprs.size() != 0 && Exprs.get() && "missing expressions");
-
   // If there is no declaration, there was an error parsing it.  Just ignore
   // the initializer.
   if (RealDecl == 0)
@@ -8912,9 +8910,18 @@ void Sema::AddCXXDirectInitializerToDecl(Decl *RealDecl,
     return;
   }
 
-  // C++0x [decl.spec.auto]p6. Deduce the type which 'auto' stands in for.
+  // C++0x [dcl.spec.auto]p6. Deduce the type which 'auto' stands in for.
   if (TypeMayContainAuto && VDecl->getType()->getContainedAutoType()) {
-    // FIXME: n3225 doesn't actually seem to indicate this is ill-formed
+    if (Exprs.size() == 0) {
+      // It isn't possible to write this directly, but it is possible to
+      // end up in this situation with "auto x(some_pack...);"
+      Diag(LParenLoc, diag::err_auto_var_init_no_expression)
+        << VDecl->getDeclName() << VDecl->getType()
+        << VDecl->getSourceRange();
+      RealDecl->setInvalidDecl();
+      return;
+    }
+
     if (Exprs.size() > 1) {
       Diag(Exprs.get()[1]->getSourceRange().getBegin(),
            diag::err_auto_var_init_multiple_expressions)

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -393,16 +393,15 @@ Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
     if (!SemaRef.InstantiateInitializer(D->getInit(), TemplateArgs, LParenLoc,
                                         InitArgs, RParenLoc)) {
       bool TypeMayContainAuto = true;
-      // Attach the initializer to the declaration, if we have one.
-      if (InitArgs.size() == 0)
-        SemaRef.ActOnUninitializedDecl(Var, TypeMayContainAuto);
-      else if (D->hasCXXDirectInitializer()) {
+      if (D->hasCXXDirectInitializer()) {
         // Add the direct initializer to the declaration.
         SemaRef.AddCXXDirectInitializerToDecl(Var,
                                               LParenLoc,
                                               move_arg(InitArgs),
                                               RParenLoc,
                                               TypeMayContainAuto);
+      } else if (InitArgs.size() == 0) {
+        SemaRef.ActOnUninitializedDecl(Var, TypeMayContainAuto);
       } else {
         assert(InitArgs.size() == 1);
         Expr *Init = InitArgs.take()[0];

clang/test/CXX/temp/temp.decls/temp.variadic/p4.cpp

@@ -37,7 +37,8 @@ template void initializer_list_expansion<1, 2, 3, 4, 5, 6>(); // expected-note{{
 namespace PR8977 {
   struct A { };
   template<typename T, typename... Args> void f(Args... args) {
-    T t(args...);
+    // An empty expression-list performs value initialization.
+    constexpr T t(args...);
   };
 
   template void f<A>();

clang/test/SemaCXX/dependent-auto.cpp

@@ -8,7 +8,7 @@ struct only {
 
 template<typename ...T>
 void f(T ...t) {
-  auto x(t...); // expected-error {{requires an initializer}} expected-error {{contains multiple expressions}}
+  auto x(t...); // expected-error {{is empty}} expected-error {{contains multiple expressions}}
   only<int> check = x;
 }