[PATCH] fix: do not complete indices for empty array subscripts

[Kyle Andelin <andelink@xxxxxxxx>]

From: Kyle Andelin <7277377+andelink@xxxxxxxxxxxxxxxxxxxxxxxx>

Small patch to ensure nonexistent indices are not offered as completion
choices when subscripting empty arrays.

The problem:

    # Clean zsh environment
    $ env -i TERM=${TERM} TERMINFO=${TERMINFO} zsh -f
    $ zmodload -i zsh/complist zsh/zle zsh/zutil
    $ autoload -Uz compinit; compinit -D
    $ zstyle ':completion:*:*:-subscript-:*' tag-order indexes parameters

    # Example arrays
    $ typeset -a arrfoo=(wheeler jump routine) arrbar=()

    $ echo ${arrfoo[        # <TAB> produces expected completion options
    1 -- wheeler  2 -- jump     3 -- routine

    $ echo ${arrbar[        # <TAB> completes to [0] and [1] despite being empty
    1  0

In the above, `arrbar` is empty and thus should not have any indices
as completion choices. After applying the attached patch, we get the
expected results:

    # Clean zsh environment
    $ env -i TERM=${TERM} TERMINFO=${TERMINFO} dist/bin/zsh-5.9.0.1-dev -f
    $ zmodload -i zsh/complist zsh/zle zsh/zutil
    $ autoload -Uz compinit; compinit -D
    $ zstyle ':completion:*:*:-subscript-:*' tag-order indexes parameters

    # Example arrays
    $ typeset -a arrfoo=(wheeler jump routine) arrbar=()

    $ echo ${arrfoo[        # <TAB> produces expected completion options
    1 -- wheeler  2 -- jump     3 -- routine

    $ echo ${arrbar[        # <TAB> instead completes to parameters as expected
    zsh: do you wish to see all 148 possibilities (25 lines)?


First time contributor here so please let me know if there is anything I need
to do different or if there are any changes you'd like to see. I also opened
a PR on GitHub as I wasn't sure which would be preferred:
https://github.com/zsh-users/zsh/pull/130

Thanks!
Kyle

---
 Completion/Zsh/Context/_subscript | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Completion/Zsh/Context/_subscript b/Completion/Zsh/Context/_subscript
index 25cedd193..67bad2862 100644
--- a/Completion/Zsh/Context/_subscript
+++ b/Completion/Zsh/Context/_subscript
@@ -98,6 +98,9 @@ elif [[ ${(Pt)${compstate[parameter]}} = array* ]]; then
   while _tags; do
     if _requested indexes; then
       ind=( {1..${#${(P)${compstate[parameter]}}}} )
+      if [[ ${ind[-1]} -eq 0 ]]; then
+        ind=()
+      fi
       if zstyle -T ":completion:${curcontext}:indexes" verbose; then
         list=()
         for i in "$ind[@]"; do
-- 
2.49.0