PR20625: Instantiate static constexpr member function of a local struct in a function template earlier.

This is necessary in order to allow the use of a constexpr member function, or
a member function with deduced return type, of a local class within a
surrounding instantiated function template specialization.

Patch by Michael Park!

This re-commits r236063, which was reverted in r236134, along with a fix for a
delayed template parsing bug that was exposed by this change.

llvm-svn: 237064

clang/lib/Parse/ParseTemplate.cpp

@@ -14,6 +14,7 @@
 #include "clang/Parse/Parser.h"
 #include "RAIIObjectsForParser.h"
 #include "clang/AST/ASTConsumer.h"
+#include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/Parse/ParseDiagnostic.h"
 #include "clang/Sema/DeclSpec.h"
@@ -1301,7 +1302,8 @@ void Parser::ParseLateTemplatedFuncDef(LateParsedTemplate &LPT) {
   TemplateParameterDepthRAII CurTemplateDepthTracker(TemplateParameterDepth);
 
   // To restore the context after late parsing.
-  Sema::ContextRAII GlobalSavedContext(Actions, Actions.CurContext);
+  Sema::ContextRAII GlobalSavedContext(
+      Actions, Actions.Context.getTranslationUnitDecl());
 
   SmallVector<ParseScope*, 4> TemplateParamScopeStack;
 

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1302,11 +1302,19 @@ Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
   // DR1484 clarifies that the members of a local class are instantiated as part
   // of the instantiation of their enclosing entity.
   if (D->isCompleteDefinition() && D->isLocalClass()) {
+    Sema::SavePendingLocalImplicitInstantiationsRAII
+        SavedPendingLocalImplicitInstantiations(SemaRef);
+
     SemaRef.InstantiateClass(D->getLocation(), Record, D, TemplateArgs,
                              TSK_ImplicitInstantiation,
                              /*Complain=*/true);
+
     SemaRef.InstantiateClassMembers(D->getLocation(), Record, TemplateArgs,
                                     TSK_ImplicitInstantiation);
+
+    // This class may have local implicit instantiations that need to be
+    // performed within this scope.
+    SemaRef.PerformPendingInstantiations(/*LocalOnly=*/true);
   }
 
   SemaRef.DiagnoseUnusedNestedTypedefs(Record);

clang/test/SemaTemplate/instantiate-local-class.cpp

@@ -1,4 +1,6 @@
 // RUN: %clang_cc1 -verify -std=c++11 %s
+// RUN: %clang_cc1 -verify -std=c++11 -fdelayed-template-parsing %s
+
 template<typename T>
 void f0() {
   struct X;
@@ -342,3 +344,16 @@ namespace PR18653 {
   };
   template struct S06<int>;
 }
+
+namespace PR20625 {
+template <typename T>
+void f() {
+  struct N {
+    static constexpr int get() { return 42; }
+  };
+  constexpr int n = N::get();
+  static_assert(n == 42, "n == 42");
+}
+
+void g() { f<void>(); }
+}