[clang][ASTImporter] add processing of SubstNonTypeTemplateParmExpr i…

…n isAncestorDeclContextOf (#74991)

Lack of processing of `SubstNonTypeTemplateParmExpr` in
`isAncestorDeclContextOf` would make `hasAutoReturnTypeDeclaredInside`
returns false and lead to infinite recursion. This patch adds the
processor and try to fix [this
issue](#74839)

Co-authored-by: huqizhi <836744285@qq.com>

clang/lib/AST/ASTImporter.cpp

@@ -3418,10 +3418,16 @@ static bool isAncestorDeclContextOf(const DeclContext *DC, const Stmt *S) {
   while (!ToProcess.empty()) {
     const Stmt *CurrentS = ToProcess.pop_back_val();
     ToProcess.append(CurrentS->child_begin(), CurrentS->child_end());
-    if (const auto *DeclRef = dyn_cast<DeclRefExpr>(CurrentS))
+    if (const auto *DeclRef = dyn_cast<DeclRefExpr>(CurrentS)) {
       if (const Decl *D = DeclRef->getDecl())
         if (isAncestorDeclContextOf(DC, D))
           return true;
+    } else if (const auto *E =
+                   dyn_cast_or_null<SubstNonTypeTemplateParmExpr>(CurrentS)) {
+      if (const Decl *D = E->getAssociatedDecl())
+        if (isAncestorDeclContextOf(DC, D))
+          return true;
+    }
   }
   return false;
 }

clang/unittests/AST/ASTImporterTest.cpp

@@ -7250,6 +7250,26 @@ TEST_P(ImportAutoFunctions, ReturnWithAutoTemplateType) {
       Lang_CXX14, /*FindLast=*/true);
 }
 
+TEST_P(ImportAutoFunctions, ReturnWithSubstNonTypeTemplateParmExpr) {
+  const char *Code =
+      R"(
+      template<int>
+      struct array {};
+
+      template <int N>
+      auto foo() { return array<N>(); }
+
+      void bar() { foo<0>(); }
+      )";
+  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) {