colors.theme.bash: pre-compute colors, startup 3x faster

[bmalehorn]

bash-it takes rather a while to startup, around 0.5 seconds on my
laptop. After a bit of timing it appears the majority of the time is
spent in themes/colors.theme.bash. The reason for that is the fancy
abstraction layers that use $(). For example, consider this code:

red="$(color reset red)"

It will go through 9 forkexecs to evaluate:

red="$(color reset red)"
    "$(__color_parse make_ansi reset red)"
    "$(__make_ansi reset red)"
    "\[\e[$(__reset red)m\]"
    "\[\e[0;$(__red)m\]"
    "\[\e[0;$(__color red)m\]"
    "\[\e[0;$(__color_normal_fg $(__color_red))m\]"
    "\[\e[0;$(__color_normal_fg 1)m\]"
    "\[\e[0;31m\]"

With all the variables in colors.theme.bash, this adds up to hundreds of
forks:

$ strace -f bash ./colors.theme.bash 2>&1 | grep clone | wc -l
649

The solution is to replace the function with its result:

-red="$(color reset red)"
+red='\[\e[0;31m\]'

This is safe, since colors.theme.bash never calls external functions or
takes any input. So, its result can be safely hard-coded.

This improves startup time dramatically. Try adding "time" to your .bashrc:

# Load Bash It
time source $BASH_IT/bash_it.sh

before:

real    0m0.462s
user    0m0.100s
sys     0m0.399s

after:

real    0m0.150s
user    0m0.091s
sys     0m0.064s

[nwinkler]

This is great - thanks!

Depending on the number of plugins that the user has enabled, the startup will still take a long time, but this is a great step to shave off a couple of seconds.

[bmalehorn]

No problem, I like making things faster.

FWIW, most of the remaining time is split between completions and plugins:

overall:
    forks: 89
    real    0m0.164s
    user    0m0.095s
    sys     0m0.072s

completion:
    forks: 7
    real    0m0.043s
    user    0m0.030s
    sys     0m0.013s

plugins:
    forks: 76
    real    0m0.104s
    user    0m0.053s
    sys     0m0.053s

alias-completion.plugin.bash:57 is the culprit for me, causing a fork() per alias, and I have about 76 aliases.

The real problem is that bash makes it difficult to get the output of bash builtins / functions without using $(). So even though completion -p may only take a few microseconds to run, we have to make it 1000x slower by forking a separate process.

[edubxb]

Great! Thanks for this big improvement!

[nwinkler]

If you have a suggestion for improving the alias completion plugin, feel free to provide a PR for it! I simply copied the code from a StackOverflow answer, and it worked fine. I must confess that I didn't look into timing or anything like that. The functionality that it provides easily makes up for the time it consumes during opening a new shell - at least for me...