[Clang][P1061] Fix template arguments in local classes

Author: ricejasonf

clang/docs/ReleaseNotes.rst

@@ -955,6 +955,7 @@ Bug Fixes to C++ Support
   consistently treat the initializer as manifestly constant-evaluated.
   (#GH135281)
 - Fix a crash in the presence of invalid base classes. (#GH147186)
+- Fix a crash with NTTP when instantiating local class.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -4412,8 +4412,12 @@ Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
       // No need to instantiate in-class initializers during explicit
       // instantiation.
       if (Field->hasInClassInitializer() && TSK == TSK_ImplicitInstantiation) {
+        // Handle local classes which could have substituted template params.
         CXXRecordDecl *ClassPattern =
-            Instantiation->getTemplateInstantiationPattern();
+            Instantiation->isLocalClass()
+                ? Instantiation->getInstantiatedFromMemberClass()
+                : Instantiation->getTemplateInstantiationPattern();
+
         DeclContext::lookup_result Lookup =
             ClassPattern->lookup(Field->getDeclName());
         FieldDecl *Pattern = Lookup.find_first<FieldDecl>();

clang/test/SemaCXX/local-class-template-param-crash.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+// expected-no-diagnostics
+
+template <int i>
+int g() {
+  return [] (auto) -> int {
+    struct L {
+      int m = i;
+    };
+    return 0;
+  } (42);
+}
+
+int v = g<1>();