Re: [PATCH RFC] diff: add SUBMODULE_DIFF format to display submodule diff

From: Stefan Beller <sbeller@google.com>
Date: Aug 9, 2016, 22:50 UTC
Message-ID: <CAGZ79kbzDhpsfpY8s=7O86_dNLA=VRkyC=8eiCqMambKvUnXmw@mail.gmail.com>
In-Reply-To: <20160809223219.17982-1-jacob.e.keller@intel.com>

On Tue, Aug 9, 2016 at 3:32 PM, Jacob Keller <jacob.e.keller@intel.com> wrote:

Show 12 quoted lines

> From: Jacob Keller <jacob.keller@gmail.com>
>
> For projects which have frequent updates to submodules it is often
> useful to be able to see a submodule update commit as a difference.
> Teach diff's --submodule= a new "diff" format which will execute a diff
> for the submodule between the old and new commit, and display it as
> a standard diff. This allows users to easily see what changed in
> a submodule without having to dig into the submodule themselves.
>
> Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
> ---
> There are no tests yet. Stefan suggested the use of child_process,

Well you said "I just want this one command but don't know where to put it " so it's natural to suggest using child_process. ;)

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> but I
> really believe there has to be some way of getting the diff without
> having to run a sub process (as this means we also can't do the diff
> without a checked out submodule). It doesn't properly handle options
> either, so a better solution would be much appreciated.

Oh right, we would need to codify all options again (and all future options, too)

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>
> I also would prefer if the diff actually prefixed the files with
> "path/to/submodule" so that it was obvious where the file was located in
> the directory.
>
> Suggestions welcome.
>
> +
> +       if (start_command(&cp))

I wonder if we want to stay single-execution here, i.e. if we rather want to use run_processes_parallel for all the submodules at the same time?

Though then non deterministic ordering may be an issue.

> +               return -1;
> +
> +       if (strbuf_read(buf, cp.out, 0) < 0)

So we keep the whole diff in memory I don't know much about the diff machinery, but I thought the rest of the diff machinery just streams it out?

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> +
> +void show_submodule_diff(FILE *f, const char *path,
> +               const char *line_prefix,
> +               unsigned char one[20], unsigned char two[20],
> +               unsigned dirty_submodule, const char *meta,
> +               const char *reset)
> +{
> +       struct strbuf buf = STRBUF_INIT;
> +       struct strbuf sb = STRBUF_INIT;
> +       const char *message = NULL;
> +
> +       if (dirty_submodule & DIRTY_SUBMODULE_UNTRACKED)
> +               fprintf(f, "%sSubmodule %s contains untracked content\n",
> +                       line_prefix, path);
> +       if (dirty_submodule & DIRTY_SUBMODULE_MODIFIED)
> +               fprintf(f, "%sSubmodule %s contains modified content\n",
> +                       line_prefix, path);
> +
> +       if (!hashcmp(one, two)) {
> +               strbuf_release(&sb);
> +               return;
> +       }
> +
> +       if (add_submodule_odb(path))
> +               message = "(not checked out)";

When not checked out, we can invoke the diff command in .git/modules/<name> as that is the git dir of the submodule, i.e. operating diff with a bare repo?

Thanks, Stefan