C++: Address review comments

Author: calumgrant

cpp/ql/src/change-notes/2024-12-18-return-stack-allocated-memory.md

@@ -1,4 +1,4 @@
 ---
 category: minorAnalysis
 ---
-* The "Returning stack-allocated memory" query (`cpp/return-stack-allocated-memory`) no longer produces results if there is an extraction error in the type of the function.
+* The "Returning stack-allocated memory" query (`cpp/return-stack-allocated-memory`) no longer produces results if there is an extraction error in the returned expression.

cpp/ql/test/query-tests/Likely Bugs/Memory Management/ReturnStackAllocatedMemory/test.cpp

@@ -250,7 +250,3 @@ void* test_strndupa(const char* s, size_t size) {
 	return s2; // BAD
 }
 
-UNKNOWN_TYPE test_error_type() {
-	UNKNOWN_TYPE x;
-	return x; // GOOD: Don't report error types
-}

cpp/ql/test/query-tests/Likely Bugs/Memory Management/ReturnStackAllocatedMemory/test_errors.cpp

@@ -0,0 +1,16 @@
+// semmle-extractor-options: --expect_errors
+
+UNKNOWN_TYPE test_error_value() {
+	UNKNOWN_TYPE x;
+	return x; // GOOD: Error return type
+}
+
+void* test_error_pointer() {
+	UNKNOWN_TYPE x;
+	return &x; // GOOD: Don't know what &x means
+}
+
+int* test_error_pointer_member() {
+	UNKNOWN_TYPE x;
+	return &x.y; // GOOD: Don't know what x.y means
+}