jsonc: handle parse errors from 'json' gracefully (fixes #2858)

- JSONDecodeError is only available in simplejson, use ValueError
- imporove error context output

ox/jsonc.py

@@ -3,6 +3,8 @@
 # vi:si:et:sw=4:sts=4:ts=4
 from __future__ import with_statement, print_function
 
+import re
+
 from .js import minify
 from .utils import json
 
@@ -14,8 +16,18 @@ def loads(source):
     try:
         minified = minify(source)
         return json.loads(minified)
-    except json.JSONDecodeError as e:
-        s = minified.split('\n')
-        context = s[e.lineno-1][max(0, e.colno-1):e.colno+30]
-        msg = e.msg + ' at ' + context
-        raise json.JSONDecodeError(msg, minified, e.pos)
+    except ValueError as e:
+        msg = e.message if hasattr(e, 'message') else str(e)
+        lineno = None
+        colno = None
+        try:
+            m = re.search(r'line (\d+) column (\d+)', msg)
+            if m:
+                (lineno, colno) = map(int, m.groups())
+        except:
+            pass
+        if lineno and colno:
+            s = minified.split('\n')
+            context = s[lineno-1][max(0, colno-30):colno+30]
+            msg += ' at:\n\n %s\n %s\033[1m^\033[0m' %(context, ' ' * (colno - max(0, colno-30) - 2))
+        raise ValueError(msg)