[PATCH] diff: handle "-" as abbreviation of '@{-1}'

[PATCH] diff: handle "-" as abbreviation of '@{-1}'

[Senorsen]

Currently it just replace "-" in argv[] into "@{-1}".

For example,

    git diff -

equals to

    git diff @{-1}

Signed-off-by: Senorsen <senorsen.zhang@gmail.com>
---
Notes:
    Hello everyone, I'm Zhang Sen, a college student from Zhejiang University 
    in China, and this is a patch for the microproject of GSoC 2016. I'm 
    looking forward to contributing to Git and participating in GSoC 2016.

    I have learnt some rules and guides from the documents, and carefully 
    wrote this small patch, according to other code from git.

    Thanks a lot!

 builtin/diff.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/builtin/diff.c b/builtin/diff.c
index 52c98a9..c110141 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -389,6 +389,11 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	for (i = 0; i < argc; i++) {
+		if (!strcmp(argv[i], "-"))
+			argv[i] = "@{-1}";
+	}
+
 	for (i = 0; i < rev.pending.nr; i++) {
 		struct object_array_entry *entry = &rev.pending.objects[i];
 		struct object *obj = entry->item;
-- 
2.7.0

Re: [PATCH] diff: handle "-" as abbreviation of '@{-1}'

[Javier Domingo Cansino]

dash is usually used for representing stdin / stdout as a file. I
think this could drive to error... but I would agree with transforming
-h1 to @{-1} or -h2 to @{-2} (-h representing head).

I do agree however that all those signs are thought with american
keyboards in mind. All those punctuation marks are usually hard to
type in other keyboards, and -h1 is way simpler than HEAD~ or @{-1}

This links provides an example of my worry:
http://stackoverflow.com/questions/15270970/is-it-possible-to-git-diff-a-file-against-standard-input

On Sat, Mar 12, 2016 at 2:11 AM, Senorsen <senorsen.zhang@gmail.com> wrote:
>
> Currently it just replace "-" in argv[] into "@{-1}".
>
> For example,
>
>     git diff -
>
> equals to
>
>     git diff @{-1}
>
> Signed-off-by: Senorsen <senorsen.zhang@gmail.com>
> ---
> Notes:
>     Hello everyone, I'm Zhang Sen, a college student from Zhejiang University
>     in China, and this is a patch for the microproject of GSoC 2016. I'm
>     looking forward to contributing to Git and participating in GSoC 2016.
>
>     I have learnt some rules and guides from the documents, and carefully
>     wrote this small patch, according to other code from git.
>
>     Thanks a lot!
>
>  builtin/diff.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/builtin/diff.c b/builtin/diff.c
> index 52c98a9..c110141 100644
> --- a/builtin/diff.c
> +++ b/builtin/diff.c
> @@ -389,6 +389,11 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
>                 }
>         }
>
> +       for (i = 0; i < argc; i++) {
> +               if (!strcmp(argv[i], "-"))
> +                       argv[i] = "@{-1}";
> +       }
> +
>         for (i = 0; i < rev.pending.nr; i++) {
>                 struct object_array_entry *entry = &rev.pending.objects[i];
>                 struct object *obj = entry->item;
> --
> 2.7.0
>
> --
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-- 
Javier Domingo Cansino

Re: [PATCH] diff: handle "-" as abbreviation of '@{-1}'

[Michael J Gruber]

Please bottom post - see below.

Javier Domingo Cansino venit, vidit, dixit 12.03.2016 03:48:
> dash is usually used for representing stdin / stdout as a file. I
> think this could drive to error... but I would agree with transforming
> -h1 to @{-1} or -h2 to @{-2} (-h representing head).
> 
> I do agree however that all those signs are thought with american
> keyboards in mind. All those punctuation marks are usually hard to
> type in other keyboards, and -h1 is way simpler than HEAD~ or @{-1}
> 
> This links provides an example of my worry:
> http://stackoverflow.com/questions/15270970/is-it-possible-to-git-diff-a-file-against-standard-input
> 
> On Sat, Mar 12, 2016 at 2:11 AM, Senorsen <senorsen.zhang@gmail.com> wrote:
>>
>> Currently it just replace "-" in argv[] into "@{-1}".
>>
>> For example,
>>
>>     git diff -
>>
>> equals to
>>
>>     git diff @{-1}
>>
>> Signed-off-by: Senorsen <senorsen.zhang@gmail.com>
>> ---
>> Notes:
>>     Hello everyone, I'm Zhang Sen, a college student from Zhejiang University
>>     in China, and this is a patch for the microproject of GSoC 2016. I'm
>>     looking forward to contributing to Git and participating in GSoC 2016.
>>
>>     I have learnt some rules and guides from the documents, and carefully
>>     wrote this small patch, according to other code from git.
>>
>>     Thanks a lot!
>>
>>  builtin/diff.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/builtin/diff.c b/builtin/diff.c
>> index 52c98a9..c110141 100644
>> --- a/builtin/diff.c
>> +++ b/builtin/diff.c
>> @@ -389,6 +389,11 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
>>                 }
>>         }
>>
>> +       for (i = 0; i < argc; i++) {
>> +               if (!strcmp(argv[i], "-"))
>> +                       argv[i] = "@{-1}";
>> +       }
>> +
>>         for (i = 0; i < rev.pending.nr; i++) {
>>                 struct object_array_entry *entry = &rev.pending.objects[i];
>>                 struct object *obj = entry->item;
>> --
>> 2.7.0
>>

Please bottom post on this list. Thanks.

In git land, "checkout", "merge" and "revert" know "-" as an
abbreviation for "@{-1}" already. No git command knows "-" as an
abbreviation for "stdin".

The analogy here is "cd -": switch to the previous directory.

So, a user can expect git to switch to the previously checked out branch
with "git checkout -".

The use of "-" in "merge" and "revert" stress that analogy quite a bit
already, and "diff" goes even further - I'm not a big fan of this. I
feel we should think about the meaning of "-":

"-" = "@{-1}": Then why not implement it at the revision machinery level
(rather than per command)? Otherwise, we raise expectations that we
don't meet.

OR:

"-" = "previous <thing>", with <thing> depending on the command context:
Then <thing> may be the content of HEAD or a commit or what not, and,
correspondingly, "-" should resolve to "@{-1}" (i.e. "HEAD@{1}") or
"HEAD^" or what not.

"git diff" is already a chameleon, diffing files, commits, blobs, index,
automatically choosing the second side in the diff if you specify only
one (or give options), and the questions which "-" blends in naturally
may very well depend on the actual color of the chameleon :)

Michael