Consider shortened debug output when there is a failure in a macro

[paulcsmith]

Let's say I have something like this that generates quite a bit of code

macro gen_tag_helpers
  {% for tag in [:a, :img, :hr, :div, :many_more_tags] %}
    def {{ tag.id }}(text)
      puts text.upcase
    end
  {% end %}
end

gen_tag_helpers

not_string = 1
# This will blow up because `1` does not implement `upcase`
img(not_string)

The output is this:

Error in macro_errors.cr:12: instantiating 'img(Int32)'

img(not_string)
^~~

in macro_errors.cr:9: expanding macro

gen_tag_helpers
^

in macro 'gen_tag_helpers' /Users/paulcsmith/learning/crystal-playground/macro_errors.cr:1, line 7:

   1.
   2.     def a(text)
   3.       puts text.upcase
   4.     end
   5.
   6.     def img(text)
>  7.       puts text.upcase
   8.     end
   9.
  10.     def hr(text)
  11.       puts text.upcase
  12.     end
  13.
  14.     def div(text)
  15.       puts text.upcase
  16.     end
  17.
+ many many more lines!

undefined method 'upcase' for Int32
Rerun with --error-trace to show a complete error trace.

The problem here is that I would expect this to be last

img(not_string)
^~~

It is super helpful that the compiler prints the macro so you can see what's wrong, but sometimes macros generate a bunch of code so finding the line that's the problem can be quite difficult. I wonder if it could print just some of the code. Maybe the 10 lines around the failure area with a compiler flag for showing everything if it's not enough. In my experience only a few lines of context are needed to see what the problem is.

It may also be helpful to colorize the line as :red so it draws attention, but that may be a separate issue.

Thanks for taking a look. Crystal rocks!

[asterite]

The last line in the error output is:

undefined method 'upcase' for Int32

The compiler always shows the relevant error last, because that's what you immediately see above the prompt. I don't think we'll change this.