[clang][ASTImporter] support import return with UnaryTransformType

[danix800]

This fixes infinite recursion crash on return with UnaryTransformType,
whose underlying type is a SubstTemplateTypeParmType which is
associated with current imported function.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Ding Fei (danix800)

Changes

This fixes infinite recursion crash on return with UnaryTransformType,
whose underlying type is a SubstTemplateTypeParmType which is
associated with current imported function.

---

Full diff: https://github.com/llvm/llvm-project/pull/101517.diff

2 Files Affected:

• (modified) clang/lib/AST/ASTImporter.cpp (+4)
• (modified) clang/unittests/AST/ASTImporterTest.cpp (+19)

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 103235547f482..157fa40163122 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -3636,6 +3636,10 @@ class IsTypeDeclaredInsideVisitor
     return {};
   }
 
+  std::optional<bool> VisitUnaryTransformType(const UnaryTransformType *T) {
+    return CheckType(T->getBaseType());
+  }
+
   std::optional<bool>
   VisitSubstTemplateTypeParmType(const SubstTemplateTypeParmType *T) {
     // The "associated declaration" can be the same as ParentDC.
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
index 57242ff49fe3b..fd9be92d3792a 100644
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -7581,6 +7581,25 @@ TEST_P(ImportAutoFunctions, ReturnWithSubstNonTypeTemplateParmExpr) {
   EXPECT_TRUE(ToBar);
 }
 
+TEST_P(ImportAutoFunctions, ReturnWithUnaryTransformType) {
+  const char *Code =
+      R"(
+        enum E { E1 };
+
+        template<typename T>
+        auto foo(T v) { return static_cast<__underlying_type(T)>(v); }
+
+        bool bar() { return foo(E1); }
+      )";
+  Decl *FromTU = getTuDecl(Code, Lang_CXX17);
+
+  auto *FromBar = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("bar")));
+
+  auto *ToBar = Import(FromBar, Lang_CXX17);
+  EXPECT_TRUE(ToBar);
+}
+
 struct ImportSourceLocations : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ImportSourceLocations, PreserveFileIDTreeStructure) {

[mizvekov]

LGTM

You can limit the amount of nodes traversed, but I don't expect this will have a significant impact.

[mizvekov]

Strictly speaking, you only need to visit the base type if the UnaryTransformType is not sugared, which currently is the same as being dependent.

Otherwise previous CheckType should have already stepped through it.