[ASTImporter] Support functions with placeholder return types ...

Summary:
Support functions with placeholder return types even in cases when the type is
declared in the body of the function.
Example: auto f() { struct X{}; return X(); }

Reviewers: balazske, a_sidorin, a.sidorin, shafik

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D70819

clang/lib/AST/ASTImporter.cpp

@@ -648,6 +648,11 @@ namespace clang {
 
     Expected<FunctionDecl *> FindFunctionTemplateSpecialization(
         FunctionDecl *FromFD);
+
+    // Returns true if the given function has a placeholder return type and
+    // that type is declared inside the body of the function.
+    // E.g. auto f() { struct X{}; return X(); }
+    bool hasAutoReturnTypeDeclaredInside(FunctionDecl *D);
   };
 
 template <typename InContainerTy>
@@ -1547,6 +1552,10 @@ Error ASTNodeImporter::ImportDeclParts(
     DeclarationName &Name, NamedDecl *&ToD, SourceLocation &Loc) {
   // Check if RecordDecl is in FunctionDecl parameters to avoid infinite loop.
   // example: int struct_in_proto(struct data_t{int a;int b;} *d);
+  // FIXME: We could support these constructs by importing a different type of
+  // this parameter and by importing the original type of the parameter only
+  // after the FunctionDecl is created. See
+  // VisitFunctionDecl::UsedDifferentProtoType.
   DeclContext *OrigDC = D->getDeclContext();
   FunctionDecl *FunDecl;
   if (isa<RecordDecl>(D) && (FunDecl = dyn_cast<FunctionDecl>(OrigDC)) &&
@@ -3005,6 +3014,46 @@ Error ASTNodeImporter::ImportFunctionDeclBody(FunctionDecl *FromFD,
   return Error::success();
 }
 
+// Returns true if the given D has a DeclContext up to the TranslationUnitDecl
+// which is equal to the given DC.
+bool isAncestorDeclContextOf(const DeclContext *DC, const Decl *D) {
+  const DeclContext *DCi = D->getDeclContext();
+  while (DCi != D->getTranslationUnitDecl()) {
+    if (DCi == DC)
+      return true;
+    DCi = DCi->getParent();
+  }
+  return false;
+}
+
+bool ASTNodeImporter::hasAutoReturnTypeDeclaredInside(FunctionDecl *D) {
+  QualType FromTy = D->getType();
+  const FunctionProtoType *FromFPT = FromTy->getAs<FunctionProtoType>();
+  assert(FromFPT && "Must be called on FunctionProtoType");
+  if (AutoType *AutoT = FromFPT->getReturnType()->getContainedAutoType()) {
+    QualType DeducedT = AutoT->getDeducedType();
+    if (const RecordType *RecordT =
+            DeducedT.isNull() ? nullptr : dyn_cast<RecordType>(DeducedT)) {
+      RecordDecl *RD = RecordT->getDecl();
+      assert(RD);
+      if (isAncestorDeclContextOf(D, RD)) {
+        assert(RD->getLexicalDeclContext() == RD->getDeclContext());
+        return true;
+      }
+    }
+  }
+  if (const TypedefType *TypedefT =
+          dyn_cast<TypedefType>(FromFPT->getReturnType())) {
+    TypedefNameDecl *TD = TypedefT->getDecl();
+    assert(TD);
+    if (isAncestorDeclContextOf(D, TD)) {
+      assert(TD->getLexicalDeclContext() == TD->getDeclContext());
+      return true;
+    }
+  }
+  return false;
+}
+
 ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
 
   SmallVector<Decl *, 2> Redecls = getCanonicalForwardRedeclChain(D);
@@ -3128,22 +3177,37 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
     return std::move(Err);
 
   QualType FromTy = D->getType();
-  bool usedDifferentExceptionSpec = false;
-
-  if (const auto *FromFPT = D->getType()->getAs<FunctionProtoType>()) {
+  // Set to true if we do not import the type of the function as is. There are
+  // cases when the original type would result in an infinite recursion during
+  // the import. To avoid an infinite recursion when importing, we create the
+  // FunctionDecl with a simplified function type and update it only after the
+  // relevant AST nodes are already imported.
+  bool UsedDifferentProtoType = false;
+  if (const auto *FromFPT = FromTy->getAs<FunctionProtoType>()) {
+    QualType FromReturnTy = FromFPT->getReturnType();
+    // Functions with auto return type may define a struct inside their body
+    // and the return type could refer to that struct.
+    // E.g.: auto foo() { struct X{}; return X(); }
+    // To avoid an infinite recursion when importing, create the FunctionDecl
+    // with a simplified return type.
+    if (hasAutoReturnTypeDeclaredInside(D)) {
+      FromReturnTy = Importer.getFromContext().VoidTy;
+      UsedDifferentProtoType = true;
+    }
     FunctionProtoType::ExtProtoInfo FromEPI = FromFPT->getExtProtoInfo();
     // FunctionProtoType::ExtProtoInfo's ExceptionSpecDecl can point to the
     // FunctionDecl that we are importing the FunctionProtoType for.
     // To avoid an infinite recursion when importing, create the FunctionDecl
-    // with a simplified function type and update it afterwards.
+    // with a simplified function type.
     if (FromEPI.ExceptionSpec.SourceDecl ||
         FromEPI.ExceptionSpec.SourceTemplate ||
         FromEPI.ExceptionSpec.NoexceptExpr) {
       FunctionProtoType::ExtProtoInfo DefaultEPI;
-      FromTy = Importer.getFromContext().getFunctionType(
-          FromFPT->getReturnType(), FromFPT->getParamTypes(), DefaultEPI);
-      usedDifferentExceptionSpec = true;
+      FromEPI = DefaultEPI;
+      UsedDifferentProtoType = true;
     }
+    FromTy = Importer.getFromContext().getFunctionType(
+        FromReturnTy, FromFPT->getParamTypes(), FromEPI);
   }
 
   QualType T;
@@ -3277,14 +3341,6 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
     }
   }
 
-  if (usedDifferentExceptionSpec) {
-    // Update FunctionProtoType::ExtProtoInfo.
-    if (ExpectedType TyOrErr = import(D->getType()))
-      ToFunction->setType(*TyOrErr);
-    else
-      return TyOrErr.takeError();
-  }
-
   // Import the describing template function, if any.
   if (FromFT) {
     auto ToFTOrErr = import(FromFT);
@@ -3316,6 +3372,14 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
       return std::move(Err);
   }
 
+  // Import and set the original type in case we used another type.
+  if (UsedDifferentProtoType) {
+    if (ExpectedType TyOrErr = import(D->getType()))
+      ToFunction->setType(*TyOrErr);
+    else
+      return TyOrErr.takeError();
+  }
+
   // FIXME: Other bits to merge?
 
   // If it is a template, import all related things.

clang/unittests/AST/ASTImporterTest.cpp

@@ -10,9 +10,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/ASTMatchers/ASTMatchers.h"
 #include "llvm/ADT/StringMap.h"
 
 #include "clang/AST/DeclContextInternals.h"
+#include "gtest/gtest.h"
 
 #include "ASTImporterFixtures.h"
 #include "MatchVerifier.h"
@@ -5623,6 +5625,188 @@ TEST_P(ASTImporterOptionSpecificTestBase, ImplicitlyDeclareSelf) {
   EXPECT_TRUE(ToMethod->getSelfDecl() != nullptr);
 }
 
+struct ImportAutoFunctions : ASTImporterOptionSpecificTestBase {};
+
+TEST_P(ImportAutoFunctions, ReturnWithTypedefDeclaredInside) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto X = [](long l) {
+        using int_type = long;
+        auto dur = 13;
+        return static_cast<int_type>(dur);
+      };
+      )",
+      Lang_CXX14, "input0.cc");
+  CXXMethodDecl *From =
+      FirstDeclMatcher<CXXMethodDecl>().match(FromTU, cxxMethodDecl());
+
+  // Explicitly set the return type of the lambda's operator() to the TypeAlias.
+  // Normally the return type would be the built-in 'long' type. However, there
+  // are cases when Clang does not use the canonical type and the TypeAlias is
+  // used. I could not create such an AST from regular source code, it requires
+  // some special state in the preprocessor. I've found such an AST when Clang
+  // parsed libcxx/src/filesystem/directory_iterator.cpp, but could not reduce
+  // that with creduce, because after preprocessing, the AST no longer
+  // contained the TypeAlias as a return type of the lambda.
+  ASTContext &Ctx = From->getASTContext();
+  TypeAliasDecl *FromTA =
+      FirstDeclMatcher<TypeAliasDecl>().match(FromTU, typeAliasDecl());
+  QualType TT = Ctx.getTypedefType(FromTA);
+  const FunctionProtoType *FPT = cast<FunctionProtoType>(From->getType());
+  QualType NewFunType =
+      Ctx.getFunctionType(TT, FPT->getParamTypes(), FPT->getExtProtoInfo());
+  From->setType(NewFunType);
+
+  CXXMethodDecl *To = Import(From, Lang_CXX14);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<TypedefType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithStructDeclaredInside) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto foo() {
+        struct X {};
+        return X();
+      }
+      )",
+      Lang_CXX14, "input0.cc");
+  FunctionDecl *From =
+      FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+
+  FunctionDecl *To = Import(From, Lang_CXX14);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithStructDeclaredInside2) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto foo() {
+        struct X {};
+        return X();
+      }
+      )",
+      Lang_CXX14, "input0.cc");
+  FunctionDecl *From =
+      FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+
+  // This time import the type directly.
+  QualType ToT = ImportType(From->getType(), From, Lang_CXX14);
+  const FunctionProtoType *FPT = cast<FunctionProtoType>(ToT);
+  EXPECT_TRUE(isa<AutoType>(FPT->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithTypedefToStructDeclaredInside) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto foo() {
+        struct X {};
+        using Y = X;
+        return Y();
+      }
+      )",
+      Lang_CXX14, "input0.cc");
+  FunctionDecl *From =
+      FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+
+  FunctionDecl *To = Import(From, Lang_CXX14);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithStructDeclaredNestedInside) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto foo() {
+        struct X { struct Y{}; };
+        return X::Y();
+      }
+      )",
+      Lang_CXX14, "input0.cc");
+  FunctionDecl *From =
+      FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+
+  FunctionDecl *To = Import(From, Lang_CXX14);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithInternalLambdaType) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto f() {
+        auto l = []() {
+          struct X {};
+          return X();
+        };
+        return l();
+      }
+      )",
+      Lang_CXX17, "input0.cc");
+  FunctionDecl *From = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("f")));
+
+  FunctionDecl *To = Import(From, Lang_CXX17);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithTypeInIf) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto f() {
+        if (struct X {} x; true)
+          return X();
+        else
+          return X();
+      }
+      )",
+      Lang_CXX17, "input0.cc");
+  FunctionDecl *From = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("f")));
+
+  FunctionDecl *To = Import(From, Lang_CXX17);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithTypeInFor) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto f() {
+        for (struct X {} x;;)
+          return X();
+      }
+      )",
+      Lang_CXX17, "input0.cc");
+  FunctionDecl *From = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("f")));
+
+  FunctionDecl *To = Import(From, Lang_CXX17);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
+TEST_P(ImportAutoFunctions, ReturnWithTypeInSwitch) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      auto f() {
+        switch (struct X {} x; 10) {
+        case 10:
+          return X();
+        }
+      }
+      )",
+      Lang_CXX17, "input0.cc");
+  FunctionDecl *From = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("f")));
+
+  FunctionDecl *To = Import(From, Lang_CXX17);
+  EXPECT_TRUE(To);
+  EXPECT_TRUE(isa<AutoType>(To->getReturnType()));
+}
+
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterLookupTableTest,
                         DefaultTestValuesForRunOptions, );
 
@@ -5650,6 +5834,9 @@ INSTANTIATE_TEST_CASE_P(ParameterizedTests, RedirectingImporterTest,
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFunctions,
                         DefaultTestValuesForRunOptions, );
 
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportAutoFunctions,
+                        DefaultTestValuesForRunOptions, );
+
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFunctionTemplates,
                         DefaultTestValuesForRunOptions, );
 

clang/unittests/AST/Language.cpp

@@ -34,6 +34,9 @@ ArgVector getBasicRunOptionsForLanguage(Language Lang) {
   case Lang_CXX14:
     BasicArgs = {"-std=c++14", "-frtti"};
     break;
+  case Lang_CXX17:
+    BasicArgs = {"-std=c++17", "-frtti"};
+    break;
   case Lang_CXX2a:
     BasicArgs = {"-std=c++2a", "-frtti"};
     break;

clang/unittests/AST/Language.h

@@ -28,6 +28,7 @@ enum Language {
     Lang_CXX,
     Lang_CXX11,
     Lang_CXX14,
+    Lang_CXX17,
     Lang_CXX2a,
     Lang_OpenCL,
     Lang_OBJCXX

clang/unittests/AST/MatchVerifier.h

@@ -108,6 +108,10 @@ testing::AssertionResult MatchVerifier<NodeType>::match(
     Args.push_back("-std=c++14");
     FileName = "input.cc";
     break;
+  case Lang_CXX17:
+    Args.push_back("-std=c++17");
+    FileName = "input.cc";
+    break;
   case Lang_CXX2a:
     Args.push_back("-std=c++2a");
     FileName = "input.cc";