[lldb] Add a test for user-defined objc_copyRealizedClassList_nolock

LLDB evaluates some utility expression to update the Objective-C class list that
ends up calling function such as `free` or `objc_copyRealizedClassList_nolock`.
This adds a test that just tries to define our own bogus version of
`objc_copyRealizedClassList_nolock`. It just tests that LLDB doesn't crash as we
currently don't have a way to tell LLDB to look for the function in a specific
library.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D107778

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/Makefile

@@ -0,0 +1,4 @@
+OBJC_SOURCES := main.m
+LD_EXTRAS := -lobjc -framework Foundation
+
+include Makefile.rules

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/TestObjCClassListFunctionFromUser.py

@@ -0,0 +1,30 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    # LLDB ends up calling the user-defined function (but at least doesn't
+    # crash).
+    @expectedFailureDarwin
+    def test(self):
+        """
+        Tests LLDB's behaviour if the user defines their own conflicting
+        objc_copyRealizedClassList_nolock function.
+        """
+
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.m"))
+
+        # Get the (dynamic) type of our 'id' variable so that our Objective-C
+        # runtime information is updated.
+        str_val = self.expect_expr("custom_class")
+        dyn_val = str_val.GetDynamicValue(lldb.eDynamicCanRunTarget)
+
+        # We should have retrieved the proper class list even in presence of
+        # the user-defined function.
+        self.assertEqual(dyn_val.GetTypeName(), "CustomClass *")

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/main.m

@@ -0,0 +1,27 @@
+#import <Foundation/Foundation.h>
+#include <stdlib.h>
+
+// A function with this signature will be called by LLDB to retrieve the
+// Objective-C class list. We shouldn't call this function that is defined
+// by the user if possible.
+Class *objc_copyRealizedClassList_nolock(unsigned int *outCount) {
+  // Don't try to implement this properly but just abort.
+  abort();
+}
+
+// Define some custom class that makes LLDB read the Objective-C class list.
+@interface CustomClass : NSObject {
+};
+@end
+@implementation CustomClass
+@end
+
+int main(int argc, char **argv) {
+  id custom_class = [[CustomClass alloc] init];
+  // Make sure our trap function is emitted but never called (the test doesn't
+  // launch the executable with any args).
+  if (argc == 123) {
+    objc_copyRealizedClassList_nolock(0);
+  }
+  return 0; // break here
+}