Prevent modifying existing targets.

A warning will be printed if it is attempted.

tools/targets/__init__.py

@@ -128,23 +128,6 @@ class Target(namedtuple("Target", "name json_data resolution_order resolution_or
     # Extra custom targets files
     __extra_target_json_files = []
 
-    @staticmethod
-    def _merge_dict(dct, merge_dct):
-        """ Recursive dict merge. Inspired by `dict.update()` however instead of
-        updating only top-level keys, dict_merge recurses down into dicts nested
-        to an arbitrary depth, updating keys. 
-        The provided  ``merge_dct`` is merged into ``dct`` in place.
-        :param dct: dict onto which the merge is executed
-        :param merge_dct: dct merged into dct
-        :return: None
-        """
-        for k, v in merge_dct.iteritems():
-            if (k in dct and isinstance(dct[k], dict)
-                    and isinstance(merge_dct[k], Mapping)):
-                Target._merge_dict(dct[k], merge_dct[k])
-            else:
-                dct[k] = merge_dct[k]
-
     @staticmethod
     @cached
     def get_json_target_data():
@@ -153,7 +136,11 @@ class Target(namedtuple("Target", "name json_data resolution_order resolution_or
                                     Target.__targets_json_location_default)
 
         for extra_target in Target.__extra_target_json_files:
-            Target._merge_dict(targets, json_file_to_dict(extra_target))
+            for k, v in json_file_to_dict(extra_target).iteritems():
+                if k in targets:
+                    print 'WARNING: Custom target "%s" cannot replace existing target.' % k
+                else:
+                    targets[k] = v
 
         return targets
 

tools/test/targets/target_test.py

@@ -76,7 +76,7 @@ class TestTargets(unittest.TestCase):
             assert TARGET_MAP['Test_Target'].core is None, \
                    "attributes should be inherited from Target"
 
-    def test_modify_default_target(self):
+    def test_modify_existing_target(self):
         """Set default targets file, then override base Target definition"""
         initial_target_json = """
         {
@@ -132,8 +132,9 @@ class TestTargets(unittest.TestCase):
                 update_target_data()
 
                 assert TARGET_MAP["Test_Target"].core == "Cortex-M4"
-                assert TARGET_MAP["Test_Target"].default_toolchain == 'GCC_ARM'
-                assert TARGET_MAP["Test_Target"].bootloader_supported == True
+                # The existing target should not be modified by custom targets
+                assert TARGET_MAP["Test_Target"].default_toolchain != 'GCC_ARM'
+                assert TARGET_MAP["Test_Target"].bootloader_supported != True
 
 
 if __name__ == '__main__':