[PATCH] completion: correct zsh detection when run from git-completion.zsh (Re: [PATCH v2] completion: reduce overhead of clearing cached --options)

From: SZEDER Gábor <szeder.dev@gmail.com>
Subject: completion: correct zsh detection when run from git-completion.zsh

v2.18.0-rc0~90^2 (completion: reduce overhead of clearing cached --options, 2018-04-18) worked around a bug in bash's "set" builtin on MacOS by using compgen instead. It was careful to avoid breaking zsh by guarding this workaround with

	if [[ -n ${ZSH_VERSION-}} ]]

Alas, this interacts poorly with git-completion.zsh's bash emulation:

	ZSH_VERSION='' . "$script"

Correct it by instead using a new GIT_SOURCING_ZSH_COMPLETION shell variable to detect whether git-completion.bash is being sourced from git-completion.zsh. This way, the zsh variant is used both when run from zsh directly and when run via git-completion.zsh.

Reproduction recipe:

 1. cd git/contrib/completion && cp git-completion.zsh _git
 2. Put the following in a new ~/.zshrc file:

 	autoload -U compinit; compinit
	autoload -U bashcompinit; bashcompinit
	fpath=(~/src/git/contrib/completion $fpath)

 3. Open zsh and "git <TAB>".

With this patch: Triggers nice git-completion.bash based tab completion

Without:
 contrib/completion/git-completion.bash:354: read-only variable: QISUFFIX
 zsh:12: command not found: ___main
 zsh:15: _default: function definition file not found
 _dispatch:70: bad math expression: operand expected at `/usr/bin/g...'
 Segmentation fault

Reported-by: Rick van Hattem <wolph@wol.ph>
Reported-by: Dave Borowitz <dborowitz@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
SZEDER Gábor wrote:

Thanks again. May we have your sign-off?

 contrib/completion/git-completion.bash | 5 ++++-
 contrib/completion/git-completion.zsh  | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)