code review 81260043: encoding/json: include Offset in SyntaxError.Error()

encoding/json: include Offset in SyntaxError.Error()
Fixes issue 7636.

[minux1, 2014-03-27 05:14:08]

Hello bradfitz@golang.org (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go

[bradfitz, 2014-03-27 18:56:46]

I'm not sure this is worth it, especially this late into Go 1.3.

A byte offset is almost always useless.  In my projects I have code to convert
it to a line & column number as well.  We might just want to do that here too. 
But not now.

[minux1, 2014-03-27 19:09:20]

On Thu, Mar 27, 2014 at 2:56 PM, <bradfitz@golang.org> wrote:

> I'm not sure this is worth it, especially this late into Go 1.3.
>
Well we exposed Offset in SyntaxError, so it makes sense to include byte
offset in error messages. Otherwise people will have to remember to also
print out err.(*SyntaxError).Offset when handling syntax errors.
(I believe most of the users just print out err, so having offset in message
might be a great help to them. Also, including all info in err.Error() seems
very common.)

>
> A byte offset is almost always useless.  In my projects I have code to
> convert it to a line & column number as well.  We might just want to do
> that here too.  But not now.
>
the user could let their editor to jump to an absolute byte offset, so I
don't
think it's useless.
line & column info is useful for human readable json, but what if the json
is
minified and it's a just huge one line string?

[bradfitz, 2014-03-27 19:24:03]

On Thu, Mar 27, 2014 at 12:09 PM, minux <minux.ma@gmail.com> wrote:

>
> On Thu, Mar 27, 2014 at 2:56 PM, <bradfitz@golang.org> wrote:
>
>> I'm not sure this is worth it, especially this late into Go 1.3.
>>
> Well we exposed Offset in SyntaxError, so it makes sense to include byte
> offset in error messages.
>

I exposed Offset in SyntaxError so Camlistore could provide good error
messages.

This patch doesn't ensure good error messages.  It just dumps the raw data
at the user.  If the user wanted the raw data, they can type-assert the
error to a SyntaxError.

I see no rush to get this in for Go 1.3.

[bradfitz, 2014-04-14 23:48:58]

R=close

Until Go 1.4.

[rsc, 2014-05-21 14:31:57]

not lgtm
the offset is often misleading because you are inside some bigger thing.
it's also a byte offset which is often useless to a person reading the error.
the one thing it is good for is extracting the offending text from the original
input argument, and for that it only needs to be an exported field.
so i think this is working as intended.