Disco prompt produces "Unknown function" error for some paths

[tocic]

1. install fish, version 3.5.1
2. cp /usr/share/fish/tools/web_config/sample_prompts/disco.fish ~/.config/fish/functions/fish_prompt.fish
3. mkdir -p /home/tocic/backup
4. cd /home/tocic/backup

Expected behaviour

Colorize the directory.

Actual behaviour

math: Error: Unknown function
'0.2126 x 0x52 + 0.7152 x 0x6b + 0.0722 x'
                                        ^
test: Missing argument at index 3
-lt 120
        ^
~/.config/fish/functions/fish_prompt.fish (line 27): 
        while test (math 0.2126 x $col[1] + 0.7152 x $col[2] + 0.0722 x $col[3]) -lt 120
              ^
in function 'fish_prompt'
in command substitution
set_color: Unknown color “526b”

Notes

The problem is that math --base=hex returns 0x526b3 for that specific path. The value can't be splitted using string match -ra .. as 3 bytes 05, 26, b3. Actually it returns just 2 52 and 6b, so $col[3] is undefined and results in the error.

The simplest solution (as far as I can tell) is to add string pad -c 0 -w 8 -r after string sub -s 3 (right padding to preserve the previous behaviour of using 0x$shas[1..3] instead of 0x$shas[2..4]; 8 because cksum uses CRC32 by default). Now we can also remove the further string pad -c 0 -w 2 call.

But with this code it's still impossible to disambiguate paths with checksums 0x526b301 and 0x526b302 because the least significant byte doesn't participate in color selection. So I think the best solution is to correctly pad the checksum (using string pad -c 0 -w 8 instead of right padding or using xargs printf '%08x' instead of math --base=hex | string sub -s 3), split it into 4 bytes and somehow use all of them to generate a color.

[faho]

Sure, done.

Using string pad is least odious. xargs in particular is an external tool and tbh terribly overused.