Re: [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>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Matthew Coleman" <matt@1eanda.com>,
	"Stephon Harris" <theonestep4@gmail.com>,
	"Duy Nguyen" <pclouds@gmail.com>,
	"Jakub Narębski" <jnareb@gmail.com>,
	"Git mailing list" <git@vger.kernel.org>,
	"Rick van Hattem" <wolph@wol.ph>,
	"Dave Borowitz" <dborowitz@google.com>
Subject: Re: [PATCH] completion: correct zsh detection when run from git-completion.zsh (Re: [PATCH v2] completion: reduce overhead of clearing cached --options)
Date: Tue, 12 Jun 2018 11:48:35 +0200	[thread overview]
Message-ID: <CAM0VKjm7Nap_tH-0Nd_QxabEPDL=71sVifo8cqhjMkqZOERJTA@mail.gmail.com> (raw)
In-Reply-To: <20180611182053.GA20665@aiede.svl.corp.google.com>

On Mon, Jun 11, 2018 at 8:20 PM, Jonathan Nieder <jrnieder@gmail.com> wrote:
> 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

Btw, even if ZSH were not to segfault, the resulting shell would be
next to useless.  The thing is that 'compgen -v foo' is supposed to
list only variable names starting with 'foo', at least that's what it
does under Bash.  In ZSH's Bash emulation, however, it lists _all_
variable names, including such fundamental env vars like PATH, HOME,
and IFS.  So when ZSH took the wrong if branch and run that

  unset $(compgen -v __gitcomp_builtin_)

then it would unset PATH and everything else as well.