dune runtest and colored strings in terminal

[sapristi]

Hello,
I noticed a strange behaviour of dune runtest.
Say I have the following file test_colors.ml :

let f s =
  output_string stdout ( "\027[34m" ^ s ^ "\027[39m"); flush stdout
    in

    for i= 1 to 20 do
      f (string_of_int i)
    done

And the dune file

(test
 (name test_colors) )

When executing dune runtest, i get the following :

where I would have expected all the characters to be colorized instead.

I have (quickly) tested with different versions of dune; I think the problem appeared in version 1.11.0

[ghost]

Ah, it's because of the way Dune handles colors in the output of commands. Basically, it's not completely pass-through; Dune parses the output of command to interpret ANSI escape sequences and then re-synthetise them. This is unless you pass --no-buffer.

I checked with strace and the string dune sends to the terminal is \33[34m1\33[0m\33[34;39;34m2\33[0m\33[34;39;34;39;34m3\33[0m\33[34;39;34;39;34;39;34m4\33[0m\33[34;39;34;39;34;39;34;39;34m5\33[0m\33[34;39;34;39;34;39;34;39;34;39;34m6.... The problem is that the ANSI escape code parser is not good enough.

Any chance you'd be interested in contributing to Dune? That's a fun self-contained project :-)

[sapristi]

Any chance you'd be interested in contributing to Dune? That's a fun self-contained project :-)
--

I will try to submit a PR when I have time to work on it :)

[ghost]

Sounds good. The code to modify is in src/stdune/ansi_colors.ml. There is a function parse that parses a string with ANSI escape sequences. It needs to be extended to recognise all SGR parameters as described on https://en.wikipedia.org/wiki/ANSI_escape_code. Then we can use a better representation of a set of styles and avoid such sequences to be generated. Feel free to change the Style.t type as well or to represent a set of styles using something else than a Style.t list.

[sapristi]

Ok, I'll check that out !