[clang] [clang][ASTImporter] support import return with UnaryTransformType (PR #101517)

[Ding Fei via cfe-commits]

https://github.com/danix800 created https://github.com/llvm/llvm-project/pull/101517

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

>From 3b787c88dafc287b9a5a7aea2afba6c3fc6dead1 Mon Sep 17 00:00:00 2001
From: dingfei <fding at feysh.com>
Date: Fri, 2 Aug 2024 00:46:57 +0800
Subject: [PATCH] [clang][ASTImporter] support import return with
 UnaryTransformType

This fixes infinite recursion crash on return with UnaryTransformType,
whose underlying type is a SubstTemplateTypeParmType which is associated
with current imported function.
---
 clang/lib/AST/ASTImporter.cpp           |  4 ++++
 clang/unittests/AST/ASTImporterTest.cpp | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

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) {