[modules] Set the lexical DC for dummy tag decls that refer to hidden

declarations that are made visible after the dummy is parsed and ODR verified

Prior to this commit the
"(getContainingDC(DC) == CurContext && "The next DeclContext should be lexically contained in the current one."),"
assertion failure was triggered during semantic analysis of the dummy
tag declaration that was declared in another tag declaration because its
lexical context did not point to the outer tag decl.

rdar://32292196

llvm-svn: 310706

clang/lib/Sema/SemaDecl.cpp

@@ -13722,6 +13722,7 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                   // comparison.
                   SkipBody->CheckSameAsPrevious = true;
                   SkipBody->New = createTagFromNewDecl();
+                  SkipBody->New->setLexicalDeclContext(CurContext);
                   SkipBody->Previous = Hidden;
                 } else {
                   SkipBody->ShouldSkip = true;

clang/test/Modules/Inputs/innerstructredef.h

@@ -0,0 +1,6 @@
+struct Outer {
+// This definition is actually hidden since only submodule 'one' is imported.
+struct Inner {
+  int x;
+} field;
+};

clang/test/Modules/Inputs/module.map

@@ -451,3 +451,12 @@ module DebugNestedB {
 module objcAtKeywordMissingEnd {
   header "objcAtKeywordMissingEnd.h"
 }
+
+module innerstructredef {
+  module one {
+    header "empty.h"
+  }
+  module two {
+   header "innerstructredef.h"
+  }
+}

clang/test/Modules/inner-struct-redefines-invisible.m

@@ -0,0 +1,12 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fsyntax-only -I%S/Inputs -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -verify %s
+// expected-no-diagnostics
+
+@import innerstructredef.one;
+
+struct Outer {
+// Should set lexical context when parsing 'Inner' here, otherwise there's a crash:
+struct Inner {
+  int x;
+} field;
+};