ANSI coloring in emacs start-process output buffer

Question

I am running a process from within emacs which uses ANSI color codes in its output.

I'm using start-process to create the process, and provided a custom buffer name for the process's output

(start-process "foo" "*Foo*" foo-command foo-args)

If I open *Foo* buffer, the ANSI color codes are printed in their raw format to the buffer

^[[36msome output message^[[m
^[[1;35msome output message^[[m
^[[1;34msome output message^[[m

I see in this SO answer it is possible to add colorization to a buffer; however I'm unsure as to how to do it with a buffer created using start-process

Is it possible to convert those ANSI color codes to colorised output in my *Foo* buffer?

Answer 1

It doesn't look like the linked answers had any solutions not involving comint-mode. You can use ansi-color-apply-on-region to colorize the output buffer, eg.

(set-process-sentinel
 (start-process "foo" "*Foo*" foo-command foo-args)
 (lambda (p _m)
   (when (eq 0 (process-exit-status p))
     (with-current-buffer (process-buffer p)
       (ansi-color-apply-on-region (point-min) (point-max))))))

Answer 2

Here's a solution that will display the colors while the process is executing (rather than after the process is complete and calling ansi-color-apply-on-region)

The key is the last line: set-process-filter.

(defun runserver ()
  (interactive)
  (setq *server-buffer* (get-buffer-create "server"))
  (with-current-buffer *server-buffer*
    (ansi-color-for-comint-mode-on)
    (comint-mode))
  (let ((default-directory "~/server/"))
    (setq *server-process*
          (start-process-shell-command
           "server" *server-buffer* "./run_server")))
  (set-process-filter *server-process* 'comint-output-filter))

A process filter function is a function that receives the standard output from the associated process. All output from that process is passed to the filter. The default filter simply outputs directly to the process buffer.