Review performance of ZSH_HIGHLIGHT_DIRS_BLACKLIST

[danielshahaf]

Here's the implementation of ZSH_HIGHLIGHT_DIRS_BLACKLIST:

zsh-syntax-highlighting/highlighters/main/main-highlighter.zsh

Lines 1229 to 1240 in e851724

	# Check if this is a blacklisted path
	if [[ $expanded_path[1] == / ]]; then
	tmp_path=$expanded_path
	else
	tmp_path=$PWD/$expanded_path
	fi
	tmp_path=$tmp_path:a
	while [[ $tmp_path != / ]]; do
	[[ -n ${(M)ZSH_HIGHLIGHT_DIRS_BLACKLIST:#$tmp_path} ]] && return 1
	tmp_path=$tmp_path:h
	done

That runs a nested loop for each ordinary (non-option) word on the command line. I suspect that's not very performant.

• Confirm whether that's performing acceptably or not

In case that's an issue, ideas:

• Special case the common case that ZSH_HIGHLIGHT_DIRS_BLACKLIST is empty.
• Join the blacklist entries into a pattern that uses alternations.
• Join the blacklist entries with NULs and use plain substring matching

The last option should be something like this:

readonly NUL=$'\0'
local -a t=( "" "${ZSH_HIGHLIGHT_DIRS_BLACKLIST[@]}" "" )
haystack="${(pj.\0.)^ZSH_HIGHLIGHT_DIRS_BLACKLIST[@]%/}/"
needle=${NUL}${expanded_arg%/}/${NUL}
if [[ $haystack == *$needle* ]]; then

That munges both the needle and the haystack by ensuring each path has a trailing slash and is both prefixed and suffixed by NULs (the latter is because /foo shouldn't match /foobar or /baz/foo).