Re: GSoC Project | Submodules related work

From: Stefan Beller <sbeller@google.com>
Date: Mar 15, 2017, 22:13 UTC
Message-ID: <CAGZ79kbV9oJp0ewp8=qz1Yts_RTDPsRW9LYcuNBQr5EFzK+VYA@mail.gmail.com>
In-Reply-To: <CAME+mvX6EH+R6xRiCCYAg_gaguv4yeFD1T765+q7F8YMppeOhw@mail.gmail.com>

On Wed, Mar 15, 2017 at 2:28 PM, Prathamesh <pc44800@gmail.com> wrote:

Show 5 quoted lines

>> What do you mean by catch here?
>
> By catching commands, I meant that we identify that the user has entered
> the command in an unpopulated or uninitialized submodule and respond
> to the user accordingly.

Well in that sense, we do not do that, yet. I see what you mean.

Show 11 quoted lines

>> However to detect if there is a submodule, we can to check two
>> things: if there is a .gitmodules entry and if there is a gitlink entry
>> recorded in the tree. Depending on the command we'd want to
>> do one before the other. e.g. git-add most likely doesn't need to
>> load .gitmodules, but may have the objects already loaded.
>> So checking if a given path is a submodule is cheap compared
>> to loading the .gitmodules file, so we'd probably want to do the
>> cheap thing first.
>
> Adding to this, we may use here this functions is_submodule_populated()
> and is_submodule_initialized() from submodule.c

Not quite, IMO.

is_submodule_initialized checks for the existence of submodule.<name>.URL in .git/config; but it sounds as if we want to check for the existence of submodule.<any name>.path in .gitmodules instead. So we'd end up using only

    module = submodule_from_path(null_sha1, path);

only from that function.

is_submodule_populated checks if there is a .git file/directory at the given path, which at this point we would know is not the case, already?

We'd roughly need to module_list_compute(... prefix = "", pathspec = prefix, ...), i.e.

    struct cache_entry *ce = lookup_cache_entry_for(prefix);
    if (ce && S_ISGITLINK(ce->ce_mode))
        /* this is an uninitialized submodule */
    else
        /* this is just a normal prefix */

Show 7 quoted lines

>> I think even when the .gitmodules file is missing, we want to have
>> some sort of warning here, as it is a confusing state to run git
>> from an uninitialized gitlink'd repository. The user may assume they
>> run the command in the gitlink'd repo, so it may be better to bail out.
>
> Can you please give an example of such situation ? I would like to
> reproduce it and think further.

I think you can create such a situation via

    git init tmp
    cd tmp
    git init gitlink
    git -C gitlink commit --allow-empty -m "initial commit"
->  git add gitlink
    git commit -m "add 'gitlink' as a gitlink"
    rm -rf gitlink
    mkdir gitlink
    git -C gitlink status

Note that we used "git add" instead of "git submodule add". git-add doesn't care about submodule, i.e. doesn't create a .gitmodules entry for you (unlike "git submodule add").

Also note that the "rm -rf && mkdir" is just a placeholder to produce this state. An alternative ending after the commit could have been

    cd ..
    git clone tmp tmp2
    cd tmp2
    git -C gitlink status

> (As even in the case where the superproject is initialized using gitlink,
> .gitmodules is in the same folder as that of the .git file containing
> GIT_DIR path)

I do not understand this?

> Also if it possible, I would like to
> work on a smaller task related to my project first, as it will help me
> understand about the project more, and which also will help me write
> my proposal for the project.

Heh, that is the beauty of open source, you don't have to ask permission. ;) But I guess this is meant as a question, on what this smaller project could be? Well as this proposal is heavy on path computation, I'd look for pathspec related leftovers at https://git-blame.blogspot.com/p/leftover-bits.html

Thanks, Stefan