refactor: simplify command extraction in zsh completion

[LangLangBart]

Description

• Resolve Completion in zsh is always based on first command #1992

The idea is to gain acces to the words array.

man 1 zshcompwid | less --pattern="^\s+words"
#   words  This  array  contains the words present on the command line currently being edited.

The great thing about this array is that the first element contains the name of
the command. The only downside is that the words array is available only in
user-defined completion widgets, which are created with zle -C, as opposed
to user-defined widgets created with zle -N.

In a command like ls; foo=bar kill **[TAB], words[1] will be kill.

To understand how the words array is constructed, one must read the zsh
source code¹.

[…] the completion system has already done the hard job (and that's not an
overstatement, I can tell you) of deciding what makes up a word on the command
line, taking into account quoting and special characters. The array of words
is stored, unsurprisingly, in the array $words.[…]

Source: A User's Guide to the Z-Shell - Chapter 6: Completion²

---

Notes

Does that mean the user has to run autoload -Uz compinit && compinit in their
setup to use fzf's completion from now on?

NO.

The new zsh completion system basically relies on shell functions, and all
of them become available as soon as the user calls compinit. Since we don't
use any of these functions here, nothing in the setup changes.

The fzf completion system is designed to be quite minimal for a couple of
commands, like kill, and to be easily extended with a shell function.

Zsh's system has become more and more sophisticated, and in version 3.1.6 a
new completion system appeared which is supposed to do everything for you: you
simply call a function, compinit, from an initialization file, after which zsh
knows, for example, that gunzip should be followed by files ending in .gz. The
new system is based on shell functions, an added bonus since they are
extremely flexible and you already know the syntax. However, given the
complexity it's quite difficult to get started writing your own completions
now, and hard enough to know what to do to change the settings the way you
like.

Source: A User's Guide to the Z-Shell - Chapter 6: Completion²

There is a very nice debug hotkey one can press, control-X + ?, and it will
list the function calls in a debug file.

man 1 zshcompsys | less --pattern _complete_debug

In the debug example below, we actually see that zsh also relies on the
words array in their _set_command³ function to extract the command that
shall be completed, and this is where the entire idea for this patch came from.

command env -i HOME=$HOME TERM=$TERM USER=$USER PATH=$PATH PAGER=$PAGER zsh -f
autoload -Uz compinit && compinit

# Enter a command, for example 'ls' and press 'control-X + ?'
ls [^X?]
# Trace output left in /tmp/zsh58725ls1 (up-history to view)
# ...

less /tmp/zsh58725ls1 ;: 'ls '
# ...
#   +_normal:37> _set_command
#    +_set_command:6> local command
#    +_set_command:8> command=ls
# ...

Footnotes

1. zsh/Code - Src/Zle/complete.c ↩

2. A User's Guide to the Z-Shell - Chapter 6: Completion, old and new ↩ ↩²

3. zsh/Code - Completion/Base/Utility/_set_command ↩

[LangLangBart]

why the test failed

  2) Failure:
TestZsh#test_dir_completion [test/test_go.rb:3684]:
Expected: "cd /tmp/fzf-test/d55/"
  Actual: "cd /tmp/fzf-test/d55"

254 runs, 2627 assertions, 1 failures, 0 errors, 1 skips

The test seems to fail due to a zsh oddity, explained below:

As it turns out, if you attempt to use completion without first defining at
least one widget, zsh automatically loads zsh/compctl just so that something
sensible will happen. The illusion of predefined completion widgets is
maintained, but it really is an illusion.

Source: https://zsh.org/mla/workers/2003/msg00703.html

Running the Docker command below and entering cd /tmp followed by pressing
TAB will not add a / (slash).

docker run --rm --tty --interactive ubuntu:24.10 sh -uec '
apt-get update && apt-get install -y zsh
rm -rf /etc/zsh
echo "testing() { : }; zle -C testing .complete-word testing" > ~/.zshenv
/usr/bin/zsh'

Running the same command without the ~/.zshenv line will cause cd /tmp[TAB]
to add the / (slash).

Widgets can be listed with zle -l.

---

The following test has been added to prevent future issues:

# Check if at least one completion system (old or new) is active
if ! zmodload -e zsh/compctl || ! (( $+functions[compdef] )); then
  zmodload -i zsh/compctl
fi

[LangLangBart]

The following test has been added to prevent future issues:

# Check if at least one completion system (old or new) is active
if ! zmodload -e zsh/compctl || ! (( $+functions[compdef] )); then
  zmodload -i zsh/compctl
fi

I would suggest adjusting the test_go.rb file instead of adding this if case
to the fzf-completion widget.

--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -3681,4 +3681,9 @@ module CompletionTest
     tmux.send_keys :BSpace, :BSpace, :BSpace
     tmux.until { |lines| assert_equal 'cd /tmp/fzf-test/d55', lines[-1] }
+    if instance_of?(TestZsh)
+      tmux.send_keys 'C-c'
+      tmux.send_keys 'zmodload -i zsh/compctl', :Enter
+      tmux.send_keys 'cd /tmp/fzf-test/d55'
+    end
     tmux.send_keys :Tab
     tmux.until { |lines| assert_equal 'cd /tmp/fzf-test/d55/', lines[-1] }

Mostly, I believe that there isn't an actual person with such a bizarre setup,
except when testing an edge case like this. (And for the use of functions, one
would need to add another check to see if the zsh/parameter module was loaded.)

Should I adjust the test file instead of the fzf-completion widget?

---

EDIT: Disregard the comment above, it is indeed a possible setup.

EDIT2: The command zmodload -i zsh/compctl should remain and be executed,
as the mere presence of zle -C … somehow hinders the dynamic loading of
zsh/compctl.

[junegunn]

Thanks! it works great as expected.