libreadline: When is the function "_rl_parse_colors()" called?

Question

I am working on Bash 5.0 from GNU repository. I wanted to debug the functions that parse the colors so I went to the colors files:

1. bash-5.0/lib/readline/colors.c - link
2. bash-5.0/lib/readline/parse-colors.c - link

I added prints like that in the function _rl_parse_colors:

printf ("[*] INSIDE _rl_parse_colors");  

I did it almost in any function but after I compiled it, I ran it but it didn't print my debug prints:

root@ubuntu:~/Desktop/bash-5.0# ./bash -c 'echo -e "\033[31mHello\e[0m World"'
Hello World

I also tried to access the bash and then run it:

root@ubuntu:~/Desktop/bash-5.0# ./bash
root@ubuntu:~/Desktop/bash-5.0# echo $BASH_VERSION                                                         
5.0.0(8)-release
root@ubuntu:~/Desktop/bash-5.0# ./bash -c 'echo -e "\033[31mHello\e[0m World"'
Hello World

It print the "Hello" with red but not my prints.
Is it related to the fact that I am using echo? I don't see how it could affect because eventfully, the bash wraps the STDOUT of the command so it should draw the string with red.

Answer 1

Found the code (I'm on the bash-5.1-testing branch) --

In file lib/readline/parse-colors.c:

300 void _rl_parse_colors(void)
301 {
302 #if defined (COLOR_SUPPORT)
303   const char *p;                /* Pointer to character being parsed */
304   char *buf;                    /* color_buf buffer pointer */
305   int state;                    /* State of parser */
306   int ind_no;                   /* Indicator number */
307   char label[3];                /* Indicator label */
308   COLOR_EXT_TYPE *ext;          /* Extension we are working on */
309
310   p = sh_get_env_value ("LS_COLORS");
311   if (p == 0 || *p == '\0')
312     {
313       _rl_color_ext_list = NULL;
314       return;
315     }
...

There's only one call of _rl_parse_colors() in file lib/readline/readline.c:

1215 /* Initialize the entire state of the world. */
1216 static void
1217 readline_initialize_everything (void)
1218 {
....
1287
1288 #if defined (COLOR_SUPPORT)
1289   if (_rl_colored_stats || _rl_colored_completion_prefix)
1290     _rl_parse_colors ();
1291 #endif
1292

The vars names _rl_colored_stats and _rl_colored_completion_prefix sound to be for these readline settings:

[STEP 101] $ bind -v | grep color
set colored-completion-prefix off
set colored-stats off
[STEP 102] $

I just verified that these steps would enter _rl_parse_colors():

1. Turn on colored-completion-prefix or colored-stats in ~/.inputrc.
2. [optional] Set (and export) LS_COLORS
3. Start an interactive shell with your compiled bash (./bash)

---

According to bash manual (man bash):

colored-completion-prefix (Off)

If set to On, when listing completions, readline displays the common prefix of the set of possible completions using a different color. The color definitions are taken from the value of the LS_COLORS environment variable.

colored-stats (Off)

If set to On, readline displays possible completions using different colors to indicate their file type. The color definitions are taken from the value of the LS_COLORS environment variable.