[modules] Do not report missing definitions of demoted constexpr variable templates. This is a followup to regression introduced in r284284. This should fix our libstdc++ modules builds.

[manmanren]

lib/Sema/SemaDecl.cpp

10129

Is the logic correct here? The if statement says !Var->isThisDeclarationADemotedDefinition(), and we then assert Var->isThisDeclarationADemotedDefinition() && getLangOpts().Modules.

[v.g.vassilev]

lib/Sema/SemaDecl.cpp

10129

Oops, that is an old version of the patch. Uploading the new one.

[rsmith]

lib/Sema/SemaDecl.cpp

10129

Can you just remove this assertion entirely? I don't see why it's relevant to what this code is checking. If we had some other reason to demote, the logic here would still seem to be correct.

[v.g.vassilev]

Remove assert.

[v.g.vassilev]

Landed in r284577.

lib/Sema/SemaDecl.cpp

     // C++11 [dcl.constexpr]p1: The constexpr specifier shall be applied only to
     // the definition of a variable [...] or the declaration of a static data
     // member.
-    if (Var->isConstexpr() && !Var->isThisDeclarationADefinition()) {
+    if (Var->isConstexpr() && !Var->isThisDeclarationADefinition() &&
+        !Var->isThisDeclarationADemotedDefinition()) {
+      assert(Var->isThisDeclarationADemotedDefinition() && getLangOpts().Modules
+             && "Demoting decls is only in the contest of modules!");
       if (Var->isStaticDataMember()) {
         // C++1z removes the relevant rule; the in-class declaration is always
         // a definition there.

test/Modules/Inputs/merge-var-template-def/a.h

 template<typename T> struct A { static bool b; };
 template<typename T> bool A<T>::b = false;
 template<typename T> void *get() { return &(A<T>::b); }
+
+template<typename T, T v>
+struct S { static constexpr T value = v; };
+template<typename T, T v>
+constexpr T S<T, v>::value;
+
 #endif

test/Modules/Inputs/merge-var-template-def/b1.h

 template<typename T> struct A { static bool b; };
 template<typename T> bool A<T>::b = false;
 template<typename T> void *get() { return &(A<T>::b); }
+
+template<typename T, T v>
+struct S { static constexpr T value = v; };
+template<typename T, T v>
+constexpr T S<T, v>::value;
+
 #include "a.h"
 #endif

test/Modules/Inputs/merge-var-template-def/b2.h

 template<typename T> struct A { static bool b; };
 template<typename T> bool A<T>::b = false;
 template<typename T> void *get() { return &(A<T>::b); }
+
+template<typename T, T v>
+struct S { static constexpr T value = v; };
+template<typename T, T v>
+constexpr T S<T, v>::value;
+
 #endif

test/Modules/merge-var-template-def.cpp

 // RUN: rm -rf %t
-// RUN: %clang_cc1 -I%S/Inputs/merge-var-template-def -verify -fmodules -Werror=undefined-internal -fmodules-local-submodule-visibility -fmodules-cache-path=%t -fimplicit-module-maps %s
+// RUN: %clang_cc1 -I%S/Inputs/merge-var-template-def -std=c++11 -verify %s
+// RUN: %clang_cc1 -I%S/Inputs/merge-var-template-def -std=c++11 -verify -fmodules -Werror=undefined-internal -fmodules-local-submodule-visibility -fmodules-cache-path=%t -fimplicit-module-maps %s
 // expected-no-diagnostics
 
 #include "b2.h"
 namespace { struct X; }
 void *x = get<X>();
+
+const bool *y = &S<bool, false>::value;