Give better error messages when parsing fails

An attempt to give slightly more helpful error messages when we have a problem
parsing an event schema file (in particular, which file contains the problem,
and which property within it).

A bit of light refactoring to make it tractable.

templating/matrix_templates/units.py

@@ -14,6 +14,7 @@ import json
 import os
 import re
 import subprocess
+import sys
 import urllib
 import yaml
 
@@ -153,21 +154,41 @@ def get_json_schema_object_fields(obj, enforce_title=False,
 
     required_keys = set(obj.get("required", []))
 
-    fields = {
-        "title": obj.get("title"),
-        "rows": []
-    }
-
-    tables = [fields]
+    obj_title = obj.get("title")
+    first_table_rows = []
+    tables = []
 
     for key_name in props:
-        logger.debug("Processing property %s.%s", obj.get('title'), key_name)
-        prop = inherit_parents(props[key_name])
+        try:
+            logger.debug("Processing property %s.%s", obj_title, key_name)
+            required = key_name in required_keys
+            res = process_prop(key_name, props[key_name], required,
+                               mark_required)
+
+            first_table_rows.append(res["row"])
+            tables.extend(res["tables"])
+            logger.debug("Done property %s" % key_name)
+
+        except Exception, e:
+            e2 = Exception("Error reading property %s.%s: %s" %
+                           (obj_title, key_name, str(e)))
+            raise e2, None, sys.exc_info()[2]
+
+
+    tables.insert(0, {
+        "title": obj_title,
+        "rows": first_table_rows,
+    })
+
+    return tables
+
+def process_prop(key_name, prop, required, mark_required):
+    prop = inherit_parents(prop)
 
     value_type = None
-        required = key_name in required_keys
     desc = prop.get("description", "")
     prop_type = prop.get('type')
+    tables = []
 
     if prop_type is None:
         raise KeyError("Property '%s' of object '%s' missing 'type' field"
@@ -233,18 +254,20 @@ def get_json_schema_object_fields(obj, enforce_title=False,
         if isinstance(value_type, list):
             value_type = " or ".join(value_type)
 
+
     if required and mark_required:
         desc = "**Required.** " + desc
-        fields["rows"].append({
+
+    return {
+        "row": {
             "key": key_name,
             "type": value_type,
             "id": value_id,
             "required": required,
             "desc": desc,
-        })
-        logger.debug("Done property %s" % key_name)
-
-    return tables
+        },
+        "tables": tables,
+    }
 
 
 def get_tables_for_schema(schema, mark_required=True):
@@ -611,9 +634,21 @@ class MatrixUnits(Units):
             if not filename.startswith("m."):
                 continue
             filepath = os.path.join(path, filename)
+            try:
+                schemata[filename] = self.read_event_schema(filepath)
+            except Exception, e:
+                e2 = Exception("Error reading event schema "+filepath+": "+
+                               str(e))
+                raise e2, None, sys.exc_info()[2]
+
+        return schemata
+
+    def read_event_schema(self, filepath):
         self.log("Reading %s" % filepath)
+
         with open(filepath, "r") as f:
             json_schema = yaml.load(f)
+
         schema = {
             "typeof": None,
             "typeof_info": "",
@@ -692,8 +727,7 @@ class MatrixUnits(Units):
                 raise Exception("Missing description for state_key")
             schema["typeof_info"] = "``state_key``: %s" % skey_desc
 
-                schemata[filename] = schema
-        return schemata
+        return schema
 
     def load_changelogs(self):
         changelogs = {}