fixup

Author: mizvekov

clang/include/clang/AST/DeclTemplate.h

@@ -1015,6 +1015,17 @@ class FunctionTemplateDecl : public RedeclarableTemplateDecl {
     return getTemplatedDecl()->isInstantiatedFromMemberTemplate() ||
            isThisDeclarationADefinition();
   }
+
+  // This bit closely tracks 'RedeclarableTemplateDecl::InstantiatedFromMember',
+  // except this is per declaration, while the redeclarable field is
+  // per chain. This indicates a template redeclaration which
+  // is compatible with the definition, in the non-trivial case
+  // where this is not already a definition.
+  // This is only really needed for instantiating the definition of friend
+  // function templates, which can have redeclarations in different template
+  // contexts.
+  // The bit is actually stored in the FunctionDecl for space efficiency
+  // reasons.
   void setInstantiatedFromMemberTemplate(FunctionTemplateDecl *D) {
     getTemplatedDecl()->setInstantiatedFromMemberTemplate();
     RedeclarableTemplateDecl::setInstantiatedFromMemberTemplate(D);