[ASTImporter] Fix missing implict CXXRecordDecl

[martong]

Summary

Implicit CXXRecordDecl is not added to its DeclContext during import, but in
the original AST it is. This patch fixes this.

[a.sidorin]

So, we fail to add injected name to a CXXRecordDecl that has a described class template? Nice catch! LGTM.

[martong]

In D46958#1101570, @a.sidorin wrote:

So, we fail to add injected name to a CXXRecordDecl that has a described class template?

Yes, we failed to import the implicit CXXRecordDecl.
Here is how it looked before the fix:

From:
ClassTemplateDecl 0xecae28 <input.cc:2:7, line:4:7> line:3:14 declToImport
|-TemplateTypeParmDecl 0xecacd8 <line:2:17, col:26> col:26 typename depth 0 index 0 U
`-CXXRecordDecl 0xecad90 <line:3:7, line:4:7> line:3:14 struct declToImport definition
  |-DefinitionData empty aggregate standard_layout trivially_copyable pod trivial literal has_constexpr_non_copy_move_ctor can_const_default_init
  | |-DefaultConstructor exists trivial constexpr needs_implicit defaulted_is_constexpr
  | |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
  | |-MoveConstructor exists simple trivial needs_implicit
  | |-CopyAssignment trivial has_const_param needs_implicit implicit_has_const_param
  | |-MoveAssignment exists simple trivial needs_implicit
  | `-Destructor simple irrelevant trivial needs_implicit
  `-CXXRecordDecl 0xecb0a0 <col:7, col:14> col:14 implicit struct declToImport
To:
ClassTemplateDecl 0xf97cb0 <input.cc:2:7, line:3:14> col:14 declToImport
|-TemplateTypeParmDecl 0xf97c00 <line:2:17, col:26> col:26 typename depth 0 index 0 U
`-CXXRecordDecl 0xf97a48 <line:3:7, col:14> col:14 struct declToImport definition
  `-DefinitionData pass_in_registers empty aggregate standard_layout trivially_copyable pod trivial literal has_constexpr_non_copy_move_ctor can_const_default_init
    |-DefaultConstructor exists trivial constexpr needs_implicit defaulted_is_constexpr
    |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
    |-MoveConstructor exists simple trivial needs_implicit
    |-CopyAssignment trivial has_const_param needs_implicit implicit_has_const_param
    |-MoveAssignment exists simple trivial needs_implicit
    `-Destructor simple irrelevant trivial needs_implicit

Thanks for the review.

cfe/trunk/lib/AST/ASTImporter.cpp

if (auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
         D2CXX = CXXRecordDecl::Create(Importer.getToContext(),
                                       D->getTagKind(),
                                       DC, StartLoc, Loc,
                                       Name.getAsIdentifierInfo());
       }
       D2 = D2CXX;
       D2->setAccess(D->getAccess());
       D2->setLexicalDeclContext(LexicalDC);
-      if (!DCXX->getDescribedClassTemplate())
+      if (!DCXX->getDescribedClassTemplate() || DCXX->isImplicit())
         LexicalDC->addDeclInternal(D2);
 
       Importer.Imported(D, D2);
 
       if (ClassTemplateDecl *FromDescribed =
           DCXX->getDescribedClassTemplate()) {
         auto *ToDescribed = cast_or_null<ClassTemplateDecl>(
             Importer.Import(FromDescribed));

cfe/trunk/unittests/AST/ASTImporterTest.cpp

TEST_P(ASTImporterTestBase,
 
   MatchVerifier<Decl> Verifier;
   ASSERT_TRUE(
       Verifier.match(From, cxxRecordDecl(hasFieldOrder({"a", "b", "c"}))));
   EXPECT_TRUE(
       Verifier.match(To, cxxRecordDecl(hasFieldOrder({"a", "b", "c"}))));
 }
 
-TEST_P(ASTImporterTestBase, DISABLED_ShouldImportImplicitCXXRecordDecl) {
+TEST_P(ASTImporterTestBase, ShouldImportImplicitCXXRecordDecl) {
   Decl *From, *To;
   std::tie(From, To) = getImportedDecl(
       R"(
       template <typename U>
       struct declToImport {
       };
       )",
       Lang_CXX, "", Lang_CXX);