Re: [PATCH v2 1/2] rev-parse: add --filename-prefix option

[Ramkumar Ramachandra <artagnon@gmail.com>]

John Keeping wrote:
> This adds a prefix string to any filename arguments encountered after it
> has been specified.

Very nice.  I thought we'd have to resort to path mangling in shell to
fix git-submodule.sh.  Glad to see that we can go with something
cleaner.

Perhaps pull some bits from your nice Documentation into the commit message?
> diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
> index f267a1d..de894c7 100644
> --- a/builtin/rev-parse.c
> +++ b/builtin/rev-parse.c
> @@ -212,11 +212,17 @@ static void show_datestring(const char *flag, const char *datestr)
>         show(buffer);
>  }
>
> -static int show_file(const char *arg)
> +static int show_file(const char *arg, int output_prefix)

Okay, so you've essentially patched show_file() to accept an
additional argument, and modified callers to call with this additional
argument.  I suppose
show_(rev|reference|default|flag|rev|with_type|datestring|abbrev)
don't need to be patched, as they are path-independent.

>  {
>         show_default();
>         if ((filter & (DO_NONFLAGS|DO_NOREV)) == (DO_NONFLAGS|DO_NOREV)) {
> -               show(arg);
> +               if (output_prefix) {
> +                       const char *prefix = startup_info->prefix;
> +                       show(prefix_filename(prefix,
> +                                            prefix ? strlen(prefix) : 0,
> +                                            arg));
> +               } else
> +                       show(arg);

Uh, why do you need output_prefix?  If startup_info->prefix is set,
use it.  Is startup_info->prefix set by anyone by cmd_rev_parse()?

> @@ -470,6 +476,7 @@ N_("git rev-parse --parseopt [options] -- [<args>...]\n"
>  int cmd_rev_parse(int argc, const char **argv, const char *prefix)
> @@ -535,6 +542,13 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
>                                 i++;
>                                 continue;
>                         }
> +                       if (!strcmp(arg, "--prefix")) {
> +                               prefix = argv[i+1];
> +                               startup_info->prefix = prefix;
> +                               output_prefix = 1;
> +                               i++;
> +                               continue;
> +                       }

Wait, why isn't prefix filled in when run_builtin() calls this?  Oh,
right: because we didn't mark this builtin with RUN_SETUP or
RUN_SETUP_GENTLY.  Okay, now why didn't we change that?  Because it
would be a major problem (all our scripts would break) if rev-parse
did cd-to-toplevel.

Why are you setting prefix to argv[i+1], and then setting
startup_info->prefix to that?  Is anyone else in cmd_rev_parse() going
to use it?

> +prefix=$(git rev-parse --show-prefix)
> +cd "$(git rev-parse --show-toplevel)"
> +eval "set -- $(git rev-parse --sq --prefix "$prefix" "$@")"

I'm wondering if you need such a convoluted usage though.  Will you
ever need to specify a prefix by hand that is different from what git
rev-parse --show-toplevel returns?  If not, why don't you just
rev-parse --emulate-toplevel, and get rid of specifying prefix by hand
altogether?  Then again, this is a plumbing command, so the simplicity
is probably more valuable.

> diff --git a/t/t1513-rev-parse-prefix.sh b/t/t1513-rev-parse-prefix.sh
> new file mode 100755
> index 0000000..5ef48d2
> --- /dev/null
> +++ b/t/t1513-rev-parse-prefix.sh
> +test_expect_success 'empty prefix -- file' '
> +       git rev-parse --prefix "" -- top sub1/file1 >actual &&
> +       cat <<-EOF >expected &&

Nit: when you're not putting in variables, you can cat <<-\EOF.

> +test_expect_success 'empty prefix HEAD:./path' '
> +       git rev-parse --prefix "" HEAD:./top >actual &&
> +       git rev-parse HEAD:top >expected &&

Nit: why did you change "./top" to "top"?  Your --prefix option
doesn't require you to change your arguments accordingly, does it?