Fix JSON graph dumping. (#5591)

* Previously this function placed a JSON-escaped string containing
   the JSON-encoded graph.

python/tvm/contrib/debugger/debug_result.py

@@ -53,9 +53,9 @@ def __init__(self, graph_json, dump_path):
         self._dump_path = dump_path
         self._output_tensor_list = []
         self._time_list = []
-        self._parse_graph(graph_json)
+        json_obj = self._parse_graph(graph_json)
         # dump the json information
-        self.dump_graph_json(graph_json)
+        self._dump_graph_json(json_obj)
 
     def _parse_graph(self, graph_json):
         """Parse and extract the JSON graph and update the nodes, shapes and dltype.
@@ -70,12 +70,12 @@ def _parse_graph(self, graph_json):
         self._shapes_list = json_obj['attrs']['shape']
         self._dtype_list = json_obj['attrs']['dltype']
         self._update_graph_json()
+        return json_obj
 
     def _update_graph_json(self):
         """update the nodes_list with name, shape and data type,
         for temporarily storing the output.
         """
-
         nodes_len = len(self._nodes_list)
         for i in range(nodes_len):
             node = self._nodes_list[i]
@@ -192,7 +192,7 @@ def node_to_events(node, times, starting_time):
         with open(os.path.join(self._dump_path, CHROME_TRACE_FILE_NAME), "w") as trace_f:
             json.dump(result, trace_f)
 
-    def dump_graph_json(self, graph):
+    def _dump_graph_json(self, graph):
         """Dump json formatted graph.
 
         Parameters

tests/python/unittest/test_runtime_graph_debug.py

@@ -14,11 +14,11 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
+import json
 import os
 import tvm
 from tvm import te
 import numpy as np
-import json
 from tvm import rpc
 from tvm.contrib import util
 from tvm.contrib.debugger import debug_runtime as graph_runtime
@@ -75,7 +75,16 @@ def check_verify():
         assert(len(os.listdir(directory)) == 1)
 
         #verify the file name is proper
-        assert(os.path.exists(os.path.join(directory, GRAPH_DUMP_FILE_NAME)))
+        graph_dump_path = os.path.join(directory, GRAPH_DUMP_FILE_NAME)
+        assert(os.path.exists(graph_dump_path))
+
+        # verify the graph contains some expected keys
+        with open(graph_dump_path) as graph_f:
+            dumped_graph = json.load(graph_f)
+
+        assert isinstance(dumped_graph, dict)
+        for k in ("nodes", "arg_nodes", "node_row_ptr", "heads", "attrs"):
+            assert k in dumped_graph, f"key {k} not in dumped graph {graph!r}"
 
         mod.run()
         #Verify the tensors are dumped