[ASTImporter] Fix 'isVirtual()' assert failure while import overridde…

…n methods

CXXMethodDecl::isVirtual() count the number of overridden methods.
This assertion is not true before overridden methods are fully loaded.
The body of this CXXMethodDecl can introduce deps on a derived class
which contains a method overriding this method, causing the assertion failure.

ImportOverriddenMethods() is moved before body loading to fix this issue.

Testcase is contributed by Balázs Kéri (balazske)

Differential Revision: https://reviews.llvm.org/D154701

clang/lib/AST/ASTImporter.cpp

@@ -3783,6 +3783,11 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
   if (Error Err = ImportTemplateInformation(D, ToFunction))
     return std::move(Err);
 
+  if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
+    if (Error Err = ImportOverriddenMethods(cast<CXXMethodDecl>(ToFunction),
+                                            FromCXXMethod))
+      return std::move(Err);
+
   if (D->doesThisDeclarationHaveABody()) {
     Error Err = ImportFunctionDeclBody(D, ToFunction);
 
@@ -3806,11 +3811,6 @@ ExpectedDecl ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
 
   addDeclToContexts(D, ToFunction);
 
-  if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
-    if (Error Err = ImportOverriddenMethods(cast<CXXMethodDecl>(ToFunction),
-                                            FromCXXMethod))
-      return std::move(Err);
-
   // Import the rest of the chain. I.e. import all subsequent declarations.
   for (++RedeclIt; RedeclIt != Redecls.end(); ++RedeclIt) {
     ExpectedDecl ToRedeclOrErr = import(*RedeclIt);

clang/unittests/AST/ASTImporterTest.cpp

@@ -2332,6 +2332,43 @@ TEST_P(ImportFunctions,
   EXPECT_EQ(ToDFOutOfClass->getPreviousDecl(), ToDFInClass);
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase,
+       ImportVirtualOverriddenMethodOnALoopTest) {
+  // B::f() calls => f1() ==> C ==> C::f()
+  //     \
+  //      \---- A::f()
+  //
+  // C::f()'s ImportOverriddenMethods() asserts B::isVirtual(), so B::f()'s
+  // ImportOverriddenMethods() should be completed before B::f()'s body
+  const char *Code =
+      R"(
+      void f1();
+      class A {
+        virtual void f(){}
+      };
+      class B: public A {
+        void f() override {
+          f1();
+        }
+      };
+      class C: public B {
+        void f() override {}
+      };
+      void f1() { C c; }
+      )";
+  Decl *FromTU = getTuDecl(Code, Lang_CXX11);
+
+  auto *FromF = FirstDeclMatcher<CXXMethodDecl>().match(
+      FromTU, cxxMethodDecl(hasName("B::f")));
+
+  auto *ToBF = Import(FromF, Lang_CXX11);
+  EXPECT_TRUE(ToBF->isVirtual());
+
+  auto *ToCF = FirstDeclMatcher<CXXMethodDecl>().match(
+      ToBF->getTranslationUnitDecl(), cxxMethodDecl(hasName("C::f")));
+  EXPECT_TRUE(ToCF->isVirtual());
+}
+
 TEST_P(ASTImporterOptionSpecificTestBase, ImportVariableChainInC) {
     std::string Code = "static int v; static int v = 0;";
     auto Pattern = varDecl(hasName("v"));