Re: [PATCH 3/5] diff: add --default-prefix option

> You can change the output of prefixes with diff.noprefix and
> diff.mnemonicprefix, but there's no easy way to override them from the
> command-line. We do have "--no-prefix", but there's no way to get back
> to the default prefix. So let's add an option to do that.
> 
> Signed-off-by: Jeff King <peff@peff.net>

> ---
> This isn't strictly necessary for the series, but it seemed like a gap.
> You can always do:
> 
>   git -c diff.noprefix=false -c diff.mnemonicprefix=false ...
> 
> but that's rather a mouthful.
> 
> Note that there isn't a command-line equivalent for mnemonicprefix,
> either. I don't think it's worth adding unless somebody really wants it.
> 
>  Documentation/diff-options.txt |  5 +++++
>  diff.c                         | 14 ++++++++++++++
>  t/t4013-diff-various.sh        | 10 ++++++++++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
> index 7d73e976d99..08ab86189a7 100644
> --- a/Documentation/diff-options.txt
> +++ b/Documentation/diff-options.txt
> @@ -852,6 +852,11 @@ endif::git-format-patch[]
>  --no-prefix::
>  	Do not show any source or destination prefix.
>  
> +--default-prefix::
> +	Use the default source and destination prefixes ("a/" and "b/").
> +	This is usually the default already, but may be used to override
> +	config such as `diff.noprefix`.
> +
>  --line-prefix=<prefix>::
>  	Prepend an additional prefix to every line of output.
>  
> diff --git a/diff.c b/diff.c
> index 750d1b1a6c3..b322e319ff3 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -5275,6 +5275,17 @@ static int diff_opt_no_prefix(const struct option *opt,
>  	return 0;
>  }
>  
> +static int diff_opt_default_prefix(const struct option *opt,
> +				   const char *optarg, int unset)
> +{
> +	struct diff_options *options = opt->value;
> +
> +	BUG_ON_OPT_NEG(unset);
> +	BUG_ON_OPT_ARG(optarg);
> +	diff_set_default_prefix(options);
> +	return 0;
> +}
> +
>  static enum parse_opt_result diff_opt_output(struct parse_opt_ctx_t *ctx,
>  					     const struct option *opt,
>  					     const char *arg, int unset)
> @@ -5564,6 +5575,9 @@ struct option *add_diff_options(const struct option *opts,
>  		OPT_CALLBACK_F(0, "no-prefix", options, NULL,
>  			       N_("do not show any source or destination prefix"),
>  			       PARSE_OPT_NONEG | PARSE_OPT_NOARG, diff_opt_no_prefix),
> +		OPT_CALLBACK_F(0, "default-prefix", options, NULL,
> +			       N_("use default prefixes a/ and b/"),
> +			       PARSE_OPT_NONEG | PARSE_OPT_NOARG, diff_opt_default_prefix),
>  		OPT_INTEGER_F(0, "inter-hunk-context", &options->interhunkcontext,
>  			      N_("show context between diff hunks up to the specified number of lines"),
>  			      PARSE_OPT_NONEG),
> diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
> index 0bc69579898..5de1d190759 100755
> --- a/t/t4013-diff-various.sh
> +++ b/t/t4013-diff-various.sh
> @@ -643,9 +643,19 @@ test_expect_success 'diff respects diff.noprefix' '
>  	check_prefix actual file0 file0
>  '
>  
> +test_expect_success 'diff --default-prefix overrides diff.noprefix' '
> +	git -c diff.noprefix diff --default-prefix >actual &&
> +	check_prefix actual a/file0 b/file0
> +'
> +
>  test_expect_success 'diff respects diff.mnemonicprefix' '
>  	git -c diff.mnemonicprefix diff >actual &&
>  	check_prefix actual i/file0 w/file0
>  '
>  
> +test_expect_success 'diff --default-prefix overrides diff.mnemonicprefix' '
> +	git -c diff.mnemonicprefix diff --default-prefix >actual &&
> +	check_prefix actual a/file0 b/file0
> +'
> +
>  test_done