Show the full error trace with Cr 0.30.0+

[bew]

With Crystal 0.30.0+, a compilation error only shows the last frame, e.g:

Showing last frame. Use --error-trace for full trace.

In /usr/lib/crystal/json/from_json.cr:136:13

 136 | yield T.new(pull)
               ^--
Error: wrong number of arguments for 'M.new' (given 1, expected 0)

Overloads are:
 - Reference.new()

When the full error trace would be:

In some_file.cr:31:5

 31 | p Q.from_json(json_queue)
          ^--------
Error: instantiating 'Array(M).class#from_json(String)'


In /usr/local/Cellar/crystal/0.30.1/src/json/from_json.cr:13:3

 13 | new parser
      ^--
Error: instantiating 'new(JSON::PullParser)'


In /usr/local/Cellar/crystal/0.30.1/src/json/from_json.cr:128:3

 128 | new(pull) do |element|
       ^--
Error: instantiating 'new(JSON::PullParser)'


In /usr/local/Cellar/crystal/0.30.1/src/json/from_json.cr:135:8

 135 | pull.read_array do
            ^---------
Error: instantiating 'JSON::PullParser#read_array()'


In /usr/local/Cellar/crystal/0.30.1/src/json/from_json.cr:135:8

 135 | pull.read_array do
            ^---------
Error: instantiating 'JSON::PullParser#read_array()'


In /usr/local/Cellar/crystal/0.30.1/src/json/from_json.cr:136:13

 136 | yield T.new(pull)
               ^--
Error: wrong number of arguments for 'M.new' (given 1, expected 0)

Overloads are:
 - Reference.new()

Which provides much more intel on the actual error.

[jhass]

Given playground examples are all single file and mostly self contained and small (way below 200LOC on average) and given the playground is a demonstration and not a development tool, I wonder if it actually wouldn't be counterproductive to do this. Wouldn't we rather risk overwhelming newcomers with the full output? After all the shortened output was introduced in the compiler, which is a development tool, to make it easier to understand even for experienced Crystal developers.

[bew]

Sure but people coming on gitter/irc uses this playground to show their ideas and more importantly their errors. And when we try to help someone with an error we might need the full error trace to help them.

For example by default the short error (a single frame) could be displayed, with a button to re-run and return the full error trace if needed.

[watzon]

There could always be an option to set flags, or at least a checkbox allowing the full error output to be displayed. That way things could be kept short and sweet normally, but if you need the full output you can get it. I'd recommend as well that flags/options like that be persisted to the database as well so that when links are shared others see exactly the same thing as you.

I've needed to be able to show the full error trace a number of times when requesting support.