encoding/json: UnmarshalTypeError should tell you what key you were unmarshaling

[kbloom]

As seen at
http://stackoverflow.com/questions/24325210/get-field-name-that-errs-in-go-json-unmarshal,
it would make it easier to debug JSON decoding errors, if UnmarshalTypeError would tell
you which key you were unmarshaling when you encountered the type error.

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-go1.4.

[gopherbot]

Comment 2:

CL https://golang.org/cl/101420043 mentions this issue.

[rsc]

Comment 3:

Some kind of better reporting would be nice but I don't think this is the right answer.

Labels changed: added release-none, removed release-go1.4.

Status changed to Accepted.

[petemoore]

I think it would be helpful here for json.UnmarshalTypeError to have a reference to the full set of bytes that were being unmarshalled, and the character location where the decoding failed. It could even print context lines with an extra line with a ^ character pointing to the problem character:

json: cannot unmarshal #/Person/properties/job/description into Go value of type string.
Failed on line 42 at character 33:
  40     "properties": {
  41         "job": {
  42             "description": 7,
                                ^
  43             "salary": 100000
  45         },

[rjeczalik]

@petemoore it's already in master by #9693. Using an offset you can then write your own tool for visualization.