Re: [RFC] extending pathspec support to submodules

Hi,

On Wed, Sep 14, 2016 at 04:57:53PM -0700, Brandon Williams wrote:

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I've been trying to think through how we could potentially add pathspec support
for --recurse-submodule options (for builtins like ls-files or grep down the
line).  This is something that could be useful if the user supply's a pathspec
that could match to a file in a submodule.  We could match the submodule to the
pathspec and then fork the process to recursively run the command on the
submodule which can be passed a modified pathspec.

For example with a pathspec 'sub/dir/a', where sub is a submodule in the root
directory of the supermodule's repo, we could match 'sub' to that spec and then
recursively call the git command with a pathspec of 'dir/a'.  The child process
would then have the responsibility of matching 'dir/a' to files in its repo.

Does this seem like a reasonable feature to add? And if so are how is my
initial approach at solving the problem?

The problem when you do that is that the child is not aware that it is
actually run as a submodule process. E.g.

   git grep --recurse-submodules foobar -- sub/dir/a

would report back matches in 'dir/a' instead of 'sub/dir/a'. From the
users perspective this will be confusing since she started the grep in
the superproject.

So what I would suggest is that we make the childs aware of the fact
that they are called from a superproject by passing a prefix when
calling it. E.g. like this

   git grep --submodule-prefix=sub foobar -- sub/dir/a

Whether we pass the full or stripped path is now a matter of taste or
ease of implementation, since we could either preprend or strip it in
the child. But the important difference is that we have information
about the original path.

Another approach could, of course, be to omit passing the prefix and
parse the output of the child and try to substitute, paths but that
seems quite error prone to me.

Cheers Heiko