[ASTImporter] Fix import of lambda in function param

Summary:
The current import implementation fails to import the definition of a
lambda class if the lambda class is defined in a function param.
E.g., the lambda class below will be imported without any methods:
```
  template <typename F>
  void f(F L = [](){}) {}
```

Reviewers: a_sidorin, a.sidorin, shafik

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64073

llvm-svn: 365315

Author: Gabor Marton

clang/lib/AST/ASTImporter.cpp

@@ -1708,8 +1708,18 @@ static Error setTypedefNameForAnonDecl(TagDecl *From, TagDecl *To,
 Error ASTNodeImporter::ImportDefinition(
     RecordDecl *From, RecordDecl *To, ImportDefinitionKind Kind) {
   if (To->getDefinition() || To->isBeingDefined()) {
-    if (Kind == IDK_Everything)
-      return ImportDeclContext(From, /*ForceImport=*/true);
+    if (Kind == IDK_Everything ||
+        // In case of lambdas, the class already has a definition ptr set, but
+        // the contained decls are not imported yet. Also, isBeingDefined was
+        // set in CXXRecordDecl::CreateLambda.  We must import the contained
+        // decls here and finish the definition.
+        (To->isLambda() && shouldForceImportDeclContext(Kind))) {
+      Error Result = ImportDeclContext(From, /*ForceImport=*/true);
+      // Finish the definition of the lambda, set isBeingDefined to false.
+      if (To->isLambda())
+        To->completeDefinition();
+      return Result;
+    }
 
     return Error::success();
   }
@@ -7422,19 +7432,10 @@ ExpectedStmt ASTNodeImporter::VisitLambdaExpr(LambdaExpr *E) {
     return ToClassOrErr.takeError();
   CXXRecordDecl *ToClass = *ToClassOrErr;
 
-  // NOTE: lambda classes are created with BeingDefined flag set up.
-  // It means that ImportDefinition doesn't work for them and we should fill it
-  // manually.
-  if (ToClass->isBeingDefined())
-    if (Error Err = ImportDeclContext(FromClass, /*ForceImport = */ true))
-      return std::move(Err);
-
   auto ToCallOpOrErr = import(E->getCallOperator());
   if (!ToCallOpOrErr)
     return ToCallOpOrErr.takeError();
 
-  ToClass->completeDefinition();
-
   SmallVector<LambdaCapture, 8> ToCaptures;
   ToCaptures.reserve(E->capture_size());
   for (const auto &FromCapture : E->captures()) {

clang/unittests/AST/ASTImporterTest.cpp

@@ -5083,6 +5083,45 @@ INSTANTIATE_TEST_CASE_P(ParameterizedTests, DeclContextTest,
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, CanonicalRedeclChain,
                         ::testing::Values(ArgVector()), );
 
+TEST_P(ASTImporterOptionSpecificTestBase, LambdaInFunctionBody) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      void f() {
+        auto L = [](){};
+      }
+      )",
+      Lang_CXX11, "input0.cc");
+  auto Pattern = lambdaExpr();
+  CXXRecordDecl *FromL =
+      FirstDeclMatcher<LambdaExpr>().match(FromTU, Pattern)->getLambdaClass();
+
+  auto ToL = Import(FromL, Lang_CXX11);
+  unsigned ToLSize = std::distance(ToL->decls().begin(), ToL->decls().end());
+  unsigned FromLSize =
+      std::distance(FromL->decls().begin(), FromL->decls().end());
+  EXPECT_NE(ToLSize, 0u);
+  EXPECT_EQ(ToLSize, FromLSize);
+}
+
+TEST_P(ASTImporterOptionSpecificTestBase, LambdaInFunctionParam) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      template <typename F>
+      void f(F L = [](){}) {}
+      )",
+      Lang_CXX11, "input0.cc");
+  auto Pattern = lambdaExpr();
+  CXXRecordDecl *FromL =
+      FirstDeclMatcher<LambdaExpr>().match(FromTU, Pattern)->getLambdaClass();
+
+  auto ToL = Import(FromL, Lang_CXX11);
+  unsigned ToLSize = std::distance(ToL->decls().begin(), ToL->decls().end());
+  unsigned FromLSize =
+      std::distance(FromL->decls().begin(), FromL->decls().end());
+  EXPECT_NE(ToLSize, 0u);
+  EXPECT_EQ(ToLSize, FromLSize);
+}
+
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterLookupTableTest,
                         DefaultTestValuesForRunOptions, );