[TOOLS] JSON upgrader to upgrade serialized json. (#4730)

During Unified IR refactor we will change the structure of IRs.
This will cause certain historical modules stored via json no longer
able to be loaded by the current version.

This PR introduces a backward compatible layer to try its best effort
to upgrade json from previous version(this case 0.6) to the current version.
We mainly aim to support update of high-level ir(relay).

python/tvm/api.py

@@ -20,7 +20,7 @@
 
 from numbers import Integral as _Integral
 
-from ._ffi.base import string_types
+from ._ffi.base import string_types, TVMError
 from ._ffi.object import register_object, Object
 from ._ffi.object import convert_to_object as _convert_to_object
 from ._ffi.object_generic import _scalar_type_inference
@@ -35,6 +35,7 @@
 from . import schedule as _schedule
 from . import container as _container
 from . import tag as _tag
+from . import json_compact
 
 int8 = "int8"
 int32 = "int32"
@@ -154,7 +155,12 @@ def load_json(json_str):
     node : Object
         The loaded tvm node.
     """
-    return _api_internal._load_json(json_str)
+
+    try:
+        return _api_internal._load_json(json_str)
+    except TVMError:
+        json_str = json_compact.upgrade_json(json_str)
+        return _api_internal._load_json(json_str)
 
 
 def save_json(node):

python/tvm/json_compact.py

@@ -0,0 +1,93 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""Tool to upgrade json from historical versions."""
+import json
+
+def create_updater(node_map, from_ver, to_ver):
+    """Create an updater to update json loaded data.
+
+    Parameters
+    ----------
+    node_map : Map[str, Function]
+        Map from type_key to updating function
+
+    from_ver : str
+        Prefix of version that we can accept,
+
+    to_ver : str
+        The target version.
+
+    Returns
+    -------
+    fupdater : function
+        The updater function
+    """
+    def _updater(data):
+        assert data["attrs"]["tvm_version"].startswith(from_ver)
+        nodes = data["nodes"]
+        for idx, item in enumerate(nodes):
+            f = node_map.get(item["type_key"], None)
+            if f:
+                nodes[idx] = f(item, nodes)
+        data["attrs"]["tvm_version"] = to_ver
+        return data
+    return _updater
+
+
+def create_updater_06_to_07():
+    """Create an update to upgrade json from v0.6 to v0.7
+
+    Returns
+    -------
+    fupdater : function
+        The updater function
+    """
+    def _ftype_var(item, nodes):
+        vindex = int(item["attrs"]["var"])
+        item["attrs"]["name_hint"] = nodes[vindex]["attrs"]["name"]
+        # set vindex to null
+        nodes[vindex]["type_key"] = ""
+        del item["attrs"]["var"]
+        return item
+
+    node_map = {
+        "relay.TypeVar": _ftype_var,
+        "relay.GlobalTypeVar": _ftype_var,
+    }
+    return create_updater(node_map, "0.6", "0.7")
+
+
+def upgrade_json(json_str):
+    """Update json from a historical version.
+
+    Parameters
+    ----------
+    json_str : str
+        A historical json file.
+
+    Returns
+    -------
+    updated_json : str
+        The updated version.
+    """
+    data = json.loads(json_str)
+    from_version = data["attrs"]["tvm_version"]
+    if from_version.startswith("0.6"):
+        data = create_updater_06_to_07()(data)
+    else:
+        raise ValueError("Cannot update from version %s" % from_version)
+    return json.dumps(data, indent=2)

tests/python/relay/test_json_compact.py

@@ -0,0 +1,47 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+import tvm
+from tvm import relay
+import json
+
+def test_type_var():
+    # type var in 0.6
+    nodes = [
+        {"type_key": ""},
+        {"type_key": "relay.TypeVar",
+         "attrs": {"kind": "0", "span": "0", "var": "2"}},
+        {"type_key": "Variable",
+         "attrs": {"dtype": "int32", "name": "in0"}},
+        ]
+    data = {
+        "root" : 1,
+        "nodes": nodes,
+        "attrs": {"tvm_version": "0.6.0"},
+        "b64ndarrays": [],
+    }
+    tvar = tvm.load_json(json.dumps(data))
+    assert isinstance(tvar, relay.TypeVar)
+    assert tvar.name_hint == "in0"
+    nodes[1]["type_key"] = "relay.GlobalTypeVar"
+    tvar = tvm.load_json(json.dumps(data))
+    assert isinstance(tvar, relay.GlobalTypeVar)
+    assert tvar.name_hint == "in0"
+
+
+if __name__ == "__main__":
+    test_type_var()