Warn if function or variable cannot be implicitly instantiated

With this patch compiler emits warning if it tries to make implicit instantiation
of a template but cannot find the template definition. The warning can be suppressed
by explicit instantiation declaration or by command line options
-Wundefined-var-template and -Wundefined-func-template. The implementation follows
the discussion of http://reviews.llvm.org/D12326.

Differential Revision: http://reviews.llvm.org/D16396

llvm-svn: 266719

clang/include/clang/AST/DeclBase.h

@@ -52,6 +52,7 @@ struct PrintingPolicy;
 class RecordDecl;
 class Stmt;
 class StoredDeclsMap;
+class TemplateDecl;
 class TranslationUnitDecl;
 class UsingDirectiveDecl;
 }
@@ -905,6 +906,10 @@ class Decl {
            DeclKind == FunctionTemplate;
   }
 
+  /// \brief If this is a declaration that describes some template, this
+  /// method returns that template declaration.
+  TemplateDecl *getDescribedTemplate() const;
+
   /// \brief Returns the function itself, or the templated function if this is a
   /// function template.
   FunctionDecl *getAsFunction() LLVM_READONLY;

clang/include/clang/Basic/DiagnosticGroups.td

@@ -75,6 +75,8 @@ def : DiagGroup<"ctor-dtor-privacy">;
 def GNUDesignator : DiagGroup<"gnu-designator">;
 def GNUStringLiteralOperatorTemplate :
   DiagGroup<"gnu-string-literal-operator-template">;
+def UndefinedVarTemplate : DiagGroup<"undefined-var-template">;
+def UndefinedFuncTemplate : DiagGroup<"undefined-func-template">;
 
 def DeleteIncomplete : DiagGroup<"delete-incomplete">;
 def DeleteNonVirtualDtor : DiagGroup<"delete-non-virtual-dtor">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3883,7 +3883,18 @@ def note_template_type_alias_instantiation_here : Note<
   "in instantiation of template type alias %0 requested here">;
 def note_template_exception_spec_instantiation_here : Note<
   "in instantiation of exception specification for %0 requested here">;
-
+def warn_var_template_missing : Warning<"instantiation of variable %q0 "
+  "required here, but no definition is available">,
+  InGroup<UndefinedVarTemplate>;
+def warn_func_template_missing : Warning<"instantiation of function %q0 "
+  "required here, but no definition is available">,
+  InGroup<UndefinedFuncTemplate>, DefaultIgnore;
+def note_forward_template_decl : Note<
+  "forward declaration of template entity is here">;
+def note_inst_declaration_hint : Note<"add an explicit instantiation "
+  "declaration to suppress this warning if %q0 is explicitly instantiated in "
+  "another translation unit">;
+
 def note_default_arg_instantiation_here : Note<
   "in instantiation of default argument for '%0' required here">;
 def note_default_function_arg_instantiation_here : Note<

clang/include/clang/Sema/Sema.h

@@ -7171,7 +7171,8 @@ class Sema {
   void InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                      FunctionDecl *Function,
                                      bool Recursive = false,
-                                     bool DefinitionRequired = false);
+                                     bool DefinitionRequired = false,
+                                     bool AtEndOfTU = false);
   VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
       VarTemplateDecl *VarTemplate, VarDecl *FromVar,
       const TemplateArgumentList &TemplateArgList,
@@ -7195,7 +7196,8 @@ class Sema {
       const MultiLevelTemplateArgumentList &TemplateArgs);
   void InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                      VarDecl *Var, bool Recursive = false,
-                                     bool DefinitionRequired = false);
+                                     bool DefinitionRequired = false,
+                                     bool AtEndOfTU = false);
   void InstantiateStaticDataMemberDefinition(
                                      SourceLocation PointOfInstantiation,
                                      VarDecl *Var,

clang/lib/AST/DeclBase.cpp

@@ -196,6 +196,17 @@ bool Decl::isTemplateDecl() const {
   return isa<TemplateDecl>(this);
 }
 
+TemplateDecl *Decl::getDescribedTemplate() const {
+  if (auto *FD = dyn_cast<FunctionDecl>(this))
+    return FD->getDescribedFunctionTemplate();
+  else if (auto *RD = dyn_cast<CXXRecordDecl>(this))
+    return RD->getDescribedClassTemplate();
+  else if (auto *VD = dyn_cast<VarDecl>(this))
+    return VD->getDescribedVarTemplate();
+
+  return nullptr;
+}
+
 const DeclContext *Decl::getParentFunctionOrMethod() const {
   for (const DeclContext *DC = getDeclContext();
        DC && !DC->isTranslationUnit() && !DC->isNamespace(); 

clang/lib/Sema/SemaOverload.cpp

@@ -9324,11 +9324,8 @@ static void DiagnoseArityMismatch(Sema &S, OverloadCandidate *Cand,
 }
 
 static TemplateDecl *getDescribedTemplate(Decl *Templated) {
-  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(Templated))
-    return FD->getDescribedFunctionTemplate();
-  else if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Templated))
-    return RD->getDescribedClassTemplate();
-
+  if (TemplateDecl *TD = Templated->getDescribedTemplate())
+    return TD;
   llvm_unreachable("Unsupported: Getting the described template declaration"
                    " for bad deduction diagnosis");
 }

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -3530,7 +3530,8 @@ TemplateDeclInstantiator::InitMethodInstantiation(CXXMethodDecl *New,
 void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                          FunctionDecl *Function,
                                          bool Recursive,
-                                         bool DefinitionRequired) {
+                                         bool DefinitionRequired,
+                                         bool AtEndOfTU) {
   if (Function->isInvalidDecl() || Function->isDefined())
     return;
 
@@ -3604,6 +3605,16 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
       assert(!Recursive);
       PendingInstantiations.push_back(
         std::make_pair(Function, PointOfInstantiation));
+    } else if (Function->getTemplateSpecializationKind()
+                 == TSK_ImplicitInstantiation) {
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
+        Diag(PointOfInstantiation, diag::warn_func_template_missing)
+          << Function;
+        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
+        if (getLangOpts().CPlusPlus11)
+          Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
+            << Function;
+      }
     }
 
     return;
@@ -3951,7 +3962,7 @@ void Sema::InstantiateStaticDataMemberDefinition(
 
 void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                          VarDecl *Var, bool Recursive,
-                                         bool DefinitionRequired) {
+                                      bool DefinitionRequired, bool AtEndOfTU) {
   if (Var->isInvalidDecl())
     return;
 
@@ -4083,6 +4094,16 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                  == TSK_ExplicitInstantiationDefinition) {
       PendingInstantiations.push_back(
         std::make_pair(Var, PointOfInstantiation));
+    } else if (Var->getTemplateSpecializationKind()
+                 == TSK_ImplicitInstantiation) {
+      // Warn about missing definition at the end of translation unit.
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
+        Diag(PointOfInstantiation, diag::warn_var_template_missing)
+          << Var;
+        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
+        if (getLangOpts().CPlusPlus11)
+          Diag(PointOfInstantiation, diag::note_inst_declaration_hint) << Var;
+      }
     }
 
     return;
@@ -4852,7 +4873,7 @@ void Sema::PerformPendingInstantiations(bool LocalOnly) {
       bool DefinitionRequired = Function->getTemplateSpecializationKind() ==
                                 TSK_ExplicitInstantiationDefinition;
       InstantiateFunctionDefinition(/*FIXME:*/Inst.second, Function, true,
-                                    DefinitionRequired);
+                                    DefinitionRequired, true);
       continue;
     }
 
@@ -4893,7 +4914,7 @@ void Sema::PerformPendingInstantiations(bool LocalOnly) {
     // Instantiate static data member definitions or variable template
     // specializations.
     InstantiateVariableDefinition(/*FIXME:*/ Inst.second, Var, true,
-                                  DefinitionRequired);
+                                  DefinitionRequired, true);
   }
 }
 

clang/test/CXX/temp/temp.decls/temp.mem/p1.cpp

@@ -10,6 +10,7 @@ template <class T> struct A {
     }
   };
 };
+extern template bool A<bool>::cond;
 
 int foo() {
   A<bool>::cond = true;

clang/test/OpenMP/parallel_ast_print.cpp

@@ -227,4 +227,7 @@ void foo(const Foo<int> &arg) {
   }
 }
 
+template<typename T>
+T S<T>::TS = 0;
+
 #endif

clang/test/OpenMP/parallel_sections_ast_print.cpp

@@ -141,4 +141,7 @@ int main(int argc, char **argv) {
   return tmain<int, 5>(b, &b) + tmain<long, 1>(x, &x);
 }
 
+template<typename T>
+T S<T>::TS = 0;
+
 #endif

clang/test/OpenMP/target_parallel_ast_print.cpp

@@ -227,4 +227,7 @@ int main (int argc, char **argv) {
   return tmain<int, 5>(argc, &argc) + tmain<char, 1>(argv[0][0], argv[0]);
 }
 
+extern template int S<int>::TS;
+extern template char S<char>::TS;
+
 #endif

clang/test/OpenMP/task_ast_print.cpp

@@ -149,4 +149,7 @@ int main(int argc, char **argv) {
   return tmain<int, 5>(b, &b) + tmain<long, 1>(x, &x);
 }
 
+extern template int S<int>::TS;
+extern template long S<long>::TS;
+
 #endif

clang/test/OpenMP/teams_ast_print.cpp

@@ -109,4 +109,6 @@ int main (int argc, char **argv) {
   return tmain<int, 5>(b, &b) + tmain<long, 1>(x, &x);
 }
 
+extern template int S<int>::TS;
+extern template long S<long>::TS;
 #endif

clang/test/OpenMP/threadprivate_ast_print.cpp

@@ -69,4 +69,5 @@ int main () {
   return (foo<int>());
 }
 
+extern template int ST<int>::m;
 #endif

clang/test/SemaCXX/PR10177.cpp

@@ -54,6 +54,7 @@ namespace N {
 
 namespace { template<typename> extern int n; }
 template<typename T> int g() { return n<int>; }
+namespace { extern template int n<int>; }
 
 #endif
 

clang/test/SemaCXX/undefined-internal.cpp

@@ -82,6 +82,7 @@ namespace test5 {
     static int var; // expected-warning {{variable 'test5::B<test5::(anonymous namespace)::A>::var' has internal linkage but is not defined}}
     static void foo(); // expected-warning {{function 'test5::B<test5::(anonymous namespace)::A>::foo' has internal linkage but is not defined}}
   };
+  extern template int B<A>::var;
 
   void test() {
     B<A>::var = 0; // expected-note {{used here}}

clang/test/SemaTemplate/undefined-template.cpp

@@ -0,0 +1,139 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 -Wundefined-func-template %s
+
+template <class T> struct C1 {
+  static char s_var_1;       // expected-note{{forward declaration of template entity is here}}
+  static char s_var_2;       // expected-note{{forward declaration of template entity is here}}
+  static void s_func_1();    // expected-note{{forward declaration of template entity is here}}
+  static void s_func_2();    // expected-note{{forward declaration of template entity is here}}
+  void meth_1();             // expected-note2{{forward declaration of template entity is here}}
+  void meth_2();
+  template <class T1> static char s_tvar_2;      // expected-note{{forward declaration of template entity is here}}
+  template <class T1> static void s_tfunc_2();   // expected-note{{forward declaration of template entity is here}}
+  template<typename T1> struct C2 {
+    static char s_var_2;     // expected-note{{forward declaration of template entity is here}}
+    static void s_func_2();  // expected-note{{forward declaration of template entity is here}}
+    void meth_2();           // expected-note{{forward declaration of template entity is here}}
+    template <class T2> static char s_tvar_2;    // expected-note{{forward declaration of template entity is here}}
+    template <class T2> void tmeth_2();          // expected-note{{forward declaration of template entity is here}}
+  };
+};
+
+extern template char C1<int>::s_var_2;
+extern template void C1<int>::s_func_2();
+extern template void C1<int>::meth_2();
+extern template char C1<int>::s_tvar_2<char>;
+extern template void C1<int>::s_tfunc_2<char>();
+extern template void C1<int>::C2<long>::s_var_2;
+extern template void C1<int>::C2<long>::s_func_2();
+extern template void C1<int>::C2<long>::meth_2();
+extern template char C1<int>::C2<long>::s_tvar_2<char>;
+extern template void C1<int>::C2<long>::tmeth_2<char>();
+
+char func_01() {
+  return C1<int>::s_var_2;
+}
+
+char func_02() {
+  return C1<int>::s_var_1; // expected-warning{{instantiation of variable 'C1<int>::s_var_1' required here, but no definition is available}}
+                           // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::s_var_1' is explicitly instantiated in another translation unit}}
+}
+
+char func_03() {
+  return C1<char>::s_var_2; // expected-warning{{instantiation of variable 'C1<char>::s_var_2' required here, but no definition is available}}
+                            // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<char>::s_var_2' is explicitly instantiated in another translation unit}}
+}
+
+void func_04() {
+  C1<int>::s_func_1(); // expected-warning{{instantiation of function 'C1<int>::s_func_1' required here, but no definition is available}}
+                       // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::s_func_1' is explicitly instantiated in another translation unit}}
+}
+
+void func_05() {
+  C1<int>::s_func_2();
+}
+
+void func_06() {
+  C1<char>::s_func_2(); // expected-warning{{instantiation of function 'C1<char>::s_func_2' required here, but no definition is available}}
+                        // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<char>::s_func_2' is explicitly instantiated in another translation unit}}
+}
+
+void func_07(C1<int> *x) {
+  x->meth_1();  // expected-warning{{instantiation of function 'C1<int>::meth_1' required here, but no definition is available}}
+                // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::meth_1' is explicitly instantiated in another translation unit}}
+}
+
+void func_08(C1<int> *x) {
+  x->meth_2();
+}
+
+void func_09(C1<char> *x) {
+  x->meth_1();  // expected-warning{{instantiation of function 'C1<char>::meth_1' required here, but no definition is available}}
+                // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<char>::meth_1' is explicitly instantiated in another translation unit}}
+}
+
+char func_10() {
+  return C1<int>::s_tvar_2<char>;
+}
+
+char func_11() {
+  return C1<int>::s_tvar_2<long>; // expected-warning{{instantiation of variable 'C1<int>::s_tvar_2<long>' required here, but no definition is available}}
+                                  // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::s_tvar_2<long>' is explicitly instantiated in another translation unit}}
+}
+
+void func_12() {
+  C1<int>::s_tfunc_2<char>();
+}
+
+void func_13() {
+  C1<int>::s_tfunc_2<long>(); // expected-warning{{instantiation of function 'C1<int>::s_tfunc_2<long>' required here, but no definition is available}}
+                              // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::s_tfunc_2<long>' is explicitly instantiated in another translation unit}}
+}
+
+char func_14() {
+  return C1<int>::C2<long>::s_var_2;
+}
+
+char func_15() {
+  return C1<int>::C2<char>::s_var_2;  //expected-warning {{instantiation of variable 'C1<int>::C2<char>::s_var_2' required here, but no definition is available}}
+                                      // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::C2<char>::s_var_2' is explicitly instantiated in another translation unit}}
+}
+
+void func_16() {
+  C1<int>::C2<long>::s_func_2();
+}
+
+void func_17() {
+  C1<int>::C2<char>::s_func_2(); // expected-warning{{instantiation of function 'C1<int>::C2<char>::s_func_2' required here, but no definition is available}}
+                        // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::C2<char>::s_func_2' is explicitly instantiated in another translation unit}}
+}
+
+void func_18(C1<int>::C2<long> *x) {
+  x->meth_2();
+}
+
+void func_19(C1<int>::C2<char> *x) {
+  x->meth_2();   // expected-warning{{instantiation of function 'C1<int>::C2<char>::meth_2' required here, but no definition is available}}
+                        // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::C2<char>::meth_2' is explicitly instantiated in another translation unit}}
+}
+
+char func_20() {
+  return C1<int>::C2<long>::s_tvar_2<char>;
+}
+
+char func_21() {
+  return C1<int>::C2<long>::s_tvar_2<long>; // expected-warning{{instantiation of variable 'C1<int>::C2<long>::s_tvar_2<long>' required here, but no definition is available}}
+                                  // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::C2<long>::s_tvar_2<long>' is explicitly instantiated in another translation unit}}
+}
+
+void func_22(C1<int>::C2<long> *x) {
+  x->tmeth_2<char>();
+}
+
+void func_23(C1<int>::C2<long> *x) {
+  x->tmeth_2<int>();    // expected-warning{{instantiation of function 'C1<int>::C2<long>::tmeth_2<int>' required here, but no definition is available}}
+                        // expected-note@-1{{add an explicit instantiation declaration to suppress this warning if 'C1<int>::C2<long>::tmeth_2<int>' is explicitly instantiated in another translation unit}}
+}
+
+int main() {
+  return 0;
+}