Re: [PATCH 1/2] Allow __git_ps1 to be used in PROMPT_COMMAND

[Junio C Hamano <gitster@pobox.com>]

Simon Oosthoek <s.oosthoek@xs4all.nl> writes:

> changes __git_ps1 to not just allow use in setting PS1
> with __git_ps1 in a command substitution, but also allows
> __git_ps1 to be used as PROMPT_COMMAND in bash.
> This has advantages for using color and I think it is more
> elegant

Is "and I think" necessary?  I do not think it matters what _you_
think when judging it is worth including in the future releases ;-)

A lot more important thing to say is why it has advantages for using
color (remember, it took a few rounds of back and forth with me).
Unless you are going to explain the same to all the people who are
reading the "git log" output 6 months down the road, that is a more
appropriate thing to write here.

>  contrib/completion/git-prompt.sh |   51 +++++++++++++++++++++++++++++++++-----
>  1 file changed, 45 insertions(+), 6 deletions(-)
>
> diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
> index 29b1ec9..c50c94a 100644
> --- a/contrib/completion/git-prompt.sh
> +++ b/contrib/completion/git-prompt.sh
> @@ -10,9 +10,14 @@
>  #    1) Copy this file to somewhere (e.g. ~/.git-prompt.sh).
>  #    2) Add the following line to your .bashrc/.zshrc:
>  #        source ~/.git-prompt.sh
> -#    3) Change your PS1 to also show the current branch:
> -#         Bash: PS1='[\u@\h \W$(__git_ps1 " (%s)")]\$ '
> -#         ZSH:  PS1='[%n@%m %c$(__git_ps1 " (%s)")]\$ '
> +#    3a) In ~/.bashrc set PROMPT_COMMAND=__git_ps1
> +#        To customize the prompt, provide start/end arguments
> +#        PROMPT_COMMAND="__git_ps1 '\u@\h:\w (' ')\$ '"
> +#    3b) Alternatively change your PS1 to call __git_ps1 as
> +#        command-substitution:
> +#        Bash: PS1='[\u@\h \W$(__git_ps1 " (%s)")]\$ '
> +#        ZSH:  PS1='[%n@%m %c$(__git_ps1 " (%s)")]\$ '
> +#        the optional argument will be used as format string
>  #
>  # The argument to __git_ps1 will be displayed only if you are currently
>  # in a git repository.  The %s token will be the name of the current
> @@ -194,11 +199,41 @@ __git_ps1_show_upstream ()
>  
>  
>  # __git_ps1 accepts 0 or 1 arguments (i.e., format string)
> +# when called from PS1 using command substitution
> +# in this mode it returns text to add to bash PS1 prompt (includes branch name) or
> +# __git_ps1 accepts 0 or 2 arguments when called from PROMPT_COMMAND
> +# in that case it _sets_ PS1. The arguments are parts of a PS1 string.
> +# when both arguments are given, the first is prepended and the second appended
> +# to the state string when assigned to PS1, otherwise default start/end strings
> +# are used.

Sorry, but I cannot parse this.  Is this meant to be a two-item list,
one describing the command substitution mode (zero or 1 arguments) and
the other describing the prompt command mode?  If so, perhaps replacing
the " or" at the end of the first item with ".\n#\n" would make it readable.

>  __git_ps1 ()
>  {
> +	local pcmode=yes
> +	local ps1pc_start='\u@\h:\w '
> +	local ps1pc_end='\$ '
> +
> +	case "$PROMPT_COMMAND" in
> +		__git_ps1*)
> +			if [ $# = 2 ]; then
> +				ps1pc_start="$1"
> +				ps1pc_end="$2"
> +			fi
> +			case "$PS1" in
> +			*__git_ps1*)
> +				echo '__git_ps1: overwriting PS1 due to PROMPT_COMMAND'

Is this supposed to be an error and/or warning message?  Why is it
worth warning only when you are overwriting __git_ps1 style of PS1
and not other user customization?

> +			;;
> +			esac
> +		;;
> +		*)  pcmode=no ;; #no output
> +	esac

Please align outer "case" "its arms)" and "esac" at the same column,
like you did for the inner "case/esac".

Auto-detetction based on PROMPT_COMMAND is a flaky approach.  In
practice, nobody will call PROMPT_COMMAND with the __git_ps1 without
any parameter (100% people want their prompt to end with some sort
of whitespace so they want the "what comes after what is computed",
aka $2), and even more importantly, nobody has been relying on use
of 0 argument form of __git_ps1 in PROMPT_COMMAND.  So why not
always require 2 args and take that as a cue to go into the pc mode?

> +
>  	local g="$(__gitdir)"
> -	if [ -n "$g" ]; then
> +	if [ -z "$g" ]; then
> +		if [ $pcmode = yes ]; then
> +			#In PC mode PS1 always needs to be set
> +			PS1="$ps1pc_start$ps1pc_end"
> +		fi
> +	else
>  		local r=""
>  		local b=""
>  		if [ -f "$g/rebase-merge/interactive" ]; then
> @@ -284,6 +319,10 @@ __git_ps1 ()
>  		fi
>  
>  		local f="$w$i$s$u"
> -		printf -- "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r$p"
> +		if [ $pcmode = yes ]; then
> +			PS1="$ps1pc_start($c${b##refs/heads/}${f:+ $f}$r$p)$ps1pc_end"
> +		elif [ $pcmode = no ]; then
> +			printf -- "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r$p"
> +		fi

Are there $pcmode other than yes or no?  Why not just "else",
instead of performing the test twice?

>  	fi
>  }