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

> Hello Peter,
> 
> On 2024-03-13 00:15, Peter Hutterer wrote:
>> Allow the default prefixes "a/" and "b/" to be tweaked by the
>> diff.srcprefix and diff.dstprefix configuration variables.
> 
> The only thing that's left is to update the patch description
> to use camel case. :)

>> 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.
>>
>>  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 &&
>