Re: [PATCH v3] diff: add diff.srcPrefix and diff.dstPrefix configuration variables

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Peter

On 12/03/2024 23:15, Peter Hutterer wrote:
> Allow the default prefixes "a/" and "b/" to be tweaked by the
> diff.srcprefix and diff.dstprefix configuration variables.
> 
> Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
> ---
> Changes to v2;
> - doc: change to camelcase diff.srcPrefix/diff.dstPrefix for
>    consistency with diff.mnemonicPrefix and most other options
> - git diff --default-prefix forces a/ and b/ regardless of configured
>    prefix, see the 'diff_opt_default_prefix' hunk in the patch below.
> 
> The latter may be slightly controversial but: there are scripts out
> there that rely on the a/ and b/ prefix (came across one last night).
> With a custom prefix those scripts will break, having an option that
> forces the a/ and b/ prefix helps. Plus the man page explicitly says:
>    Use the default source and destination prefixes ("a/" and "b/").
> So let's stick with that behaviour then.

As I understand it the purpose of --default-prefix is to override all 
the prefix related config settings so this seems like a very sensible 
choice.

Best Wishes

Phillip

>   Documentation/config/diff.txt |  6 ++++++
>   diff.c                        | 14 ++++++++++++--
>   t/t4013-diff-various.sh       | 35 +++++++++++++++++++++++++++++++++++
>   3 files changed, 53 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/config/diff.txt b/Documentation/config/diff.txt
> index 6c7e09a1ef5e..afc23d7723b6 100644
> --- a/Documentation/config/diff.txt
> +++ b/Documentation/config/diff.txt
> @@ -111,6 +111,12 @@ diff.mnemonicPrefix::
>   diff.noprefix::
>   	If set, 'git diff' does not show any source or destination prefix.
>   
> +diff.srcPrefix::
> +	If set, 'git diff' uses this source prefix. Defaults to 'a/'.
> +
> +diff.dstPrefix::
> +	If set, 'git diff' uses this destination prefix. Defaults to 'b/'.
> +
>   diff.relative::
>   	If set to 'true', 'git diff' does not show changes outside of the directory
>   	and show pathnames relative to the current directory.
> diff --git a/diff.c b/diff.c
> index e50def45383e..108c1875775d 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -62,6 +62,8 @@ static const char *diff_order_file_cfg;
>   int diff_auto_refresh_index = 1;
>   static int diff_mnemonic_prefix;
>   static int diff_no_prefix;
> +static const char *diff_src_prefix = "a/";
> +static const char *diff_dst_prefix = "b/";
>   static int diff_relative;
>   static int diff_stat_name_width;
>   static int diff_stat_graph_width;
> @@ -408,6 +410,12 @@ int git_diff_ui_config(const char *var, const char *value,
>   		diff_no_prefix = git_config_bool(var, value);
>   		return 0;
>   	}
> +	if (!strcmp(var, "diff.srcprefix")) {
> +		return git_config_string(&diff_src_prefix, var, value);
> +	}
> +	if (!strcmp(var, "diff.dstprefix")) {
> +		return git_config_string(&diff_dst_prefix, var, value);
> +	}
>   	if (!strcmp(var, "diff.relative")) {
>   		diff_relative = git_config_bool(var, value);
>   		return 0;
> @@ -3425,8 +3433,8 @@ void diff_set_noprefix(struct diff_options *options)
>   
>   void diff_set_default_prefix(struct diff_options *options)
>   {
> -	options->a_prefix = "a/";
> -	options->b_prefix = "b/";
> +	options->a_prefix = diff_src_prefix;
> +	options->b_prefix = diff_dst_prefix;
>   }
>   
>   struct userdiff_driver *get_textconv(struct repository *r,
> @@ -5362,6 +5370,8 @@ static int diff_opt_default_prefix(const struct option *opt,
>   
>   	BUG_ON_OPT_NEG(unset);
>   	BUG_ON_OPT_ARG(optarg);
> +	diff_src_prefix = "a/";
> +	diff_dst_prefix = "b/";
>   	diff_set_default_prefix(options);
>   	return 0;
>   }
> diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
> index 1e3b2dbea484..e75f9f7d4cb2 100755
> --- a/t/t4013-diff-various.sh
> +++ b/t/t4013-diff-various.sh
> @@ -663,6 +663,41 @@ test_expect_success 'diff --default-prefix overrides diff.mnemonicprefix' '
>   	check_prefix actual a/file0 b/file0
>   '
>   
> +test_expect_success 'diff respects diff.srcprefix' '
> +	git -c diff.srcprefix=x/ diff >actual &&
> +	check_prefix actual x/file0 b/file0
> +'
> +
> +test_expect_success 'diff respects diff.dstprefix' '
> +	git -c diff.dstprefix=y/ diff >actual &&
> +	check_prefix actual a/file0 y/file0
> +'
> +
> +test_expect_success 'diff --src-prefix overrides diff.srcprefix' '
> +	git -c diff.srcprefix=z/ diff --src-prefix=z/ >actual &&
> +	check_prefix actual z/file0 b/file0
> +'
> +
> +test_expect_success 'diff --dst-prefix overrides diff.dstprefix' '
> +	git -c diff.dstprefix=y/ diff --dst-prefix=z/ >actual &&
> +	check_prefix actual a/file0 z/file0
> +'
> +
> +test_expect_success 'diff src/dstprefix ignored with diff.noprefix' '
> +	git -c diff.dstprefix=y/ -c diff.srcprefix=x/ -c diff.noprefix diff >actual &&
> +	check_prefix actual file0 file0
> +'
> +
> +test_expect_success 'diff src/dstprefix ignored with diff.mnemonicprefix' '
> +	git -c diff.dstprefix=x/ -c diff.srcprefix=y/ -c diff.mnemonicprefix diff >actual &&
> +	check_prefix actual i/file0 w/file0
> +'
> +
> +test_expect_success 'diff src/dstprefix ignored with --default-prefix' '
> +	git -c diff.dstprefix=x/ -c diff.srcprefix=y/ diff --default-prefix >actual &&
> +	check_prefix actual a/file0 b/file0
> +'
> +
>   test_expect_success 'diff --no-renames cannot be abbreviated' '
>   	test_expect_code 129 git diff --no-rename >actual 2>error &&
>   	test_must_be_empty actual &&