Re: [PATCH v5 9/9] submodule: support reading .gitmodules when it's not in the working tree

[Antonio Ospite <ao2@ao2.it>]

Hi Stefan,

On Mon, 24 Sep 2018 14:00:50 -0700
Stefan Beller <sbeller@google.com> wrote:

> On Mon, Sep 24, 2018 at 3:20 AM Antonio Ospite <ao2@ao2.it> wrote:
> 
[...]
> > This is a limitation of the object store in git, there is no equivalent
> > of get_oid() to get the oid from a specific repository and this affects
> > config_with_options too when the config source is a blob.
> 
> Not yet, as there is a big push to pass-through an object-store object
> or similar recently and rely less on global variables.
> I am not sure I get to this code, though.
>

If you end up touching get_oid() please CC me.

> > This does not affect commands called via "git -C submodule_dir cmd"
> > because in that case the chdir happens before the_repository is set up,
> > for instance "git-submodule $SOMETHING --recursive" commands seem to
> > change the working directory before the recursion.
> 
> For this it may be worth looking into the option
>        --super-prefix=<path>
>   Currently for internal use only. Set a prefix which gives a
>   path from above a repository down to its root. One use is
>   to give submodules context about the superproject that
>   invoked it.
>

My comment wanted to highlight that there are NO problems in the
mentioned cases:

  - git -C submodule_dir cmd
  - git submodule cmd --recursive

Are you suggesting to look into super-prefix for any reason in
particular?

[...]
> > The test suite passes even after removing repo_read_gitmodules()
> > entirely from builtin/grep.c, but I am still not confident that I get
> > all the implication of why that call was originally added in commit
> > f9ee2fcdfa (grep: recurse in-process using 'struct repository',
> > 2017-08-02).
> 
> If you checkout that commit and remove the call to repo_read_gitmodules
> and then call git-grep in a superproject with nested submodules, you
> get a segfault.
> 
> On master (and deleting out that line) you do not get the segfault,
> I think praise goes to ff6f1f564c4 (submodule-config: lazy-load a
> repository's .gitmodules file, 2017-08-03) which happened shortly
> after f9ee2fcdfa.
> 
> It showcased that it worked by converting ls-files, but left out grep.
> 
> So I think based on ff6f1f564c4 it is safe to remove all calls to
> repo_read_gitmodules.
>

Thanks for confirming.

> > Anyways, even if we removed the call we would prevent the problem from
> > happening in the test suite, but not in the real world, in case non-leaf
> > submodules without .gitmodules in their working tree.
> 
> Quite frankly I think grep was just overlooked in review of
> https://public-inbox.org/git/20170803182000.179328-14-bmwill@google.com/
> 

OK, so the plan for v6 is:

  - avoid the corruption issues spotted by Gábor by removing the call
    to repo_read_gitmodules in builtin/grep.c (this still does not fix
    the potential problem with nested submodules).

  - add a new test-tool which better exercises the new
    config_from_gitmodules code,

  - add also a test_expect_failure test to document the use case that
    cannot be supported yet: nested submodules without .gitmodules in
    their working tree.

Thanks,
   Antonio

-- 
Antonio Ospite
https://ao2.it
https://twitter.com/ao2it

A: Because it messes up the order in which people normally read text.
   See http://en.wikipedia.org/wiki/Posting_style
Q: Why is top-posting such a bad thing?