Re: [PATCH 4/5] backfill: work with prefix pathspecs

[Derrick Stolee <stolee@gmail.com>]

On 3/17/2026 6:10 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Derrick Stolee <stolee@gmail.com>
>>
>> The previous change allowed specifying revision arguments over the 'git
>> backfill' command-line. This created the opportunity for pathspecs that
>> specify a smaller set of starting commits, but otherwise did not restrict
>> the blob paths that were downloaded.
> 
> "pathspecs that specify a smaller set of starting commits" is
> puzzling, as starting commits would be coming from the revision
> arguments.  "opportunity for pathspec to further filter commits
> to those that touch only the matching paths...", or something?

You're right. I'm using "starting commits" incorrectly. My view was too
focused on how the path-walk API starts from the commits output by the
revision walk to get a list of root trees and then walks by path from
that point.

I'll reword to make this more clear.

>> Update the path-walk API to accept certain kinds of pathspecs and to
>> silently ignore anything too complex.
> 
> Hmph, "silently ignore", instead of "no, you cannot use that! and
> die", or at least "sorry, I cannot do that, so the result may not be
> what you wanted, you've been warned"?

The behavior when silently ignoring is to over-download. The revision
walk still filters commits, but the path-walk then walks paths beyond
that pathspec. This will be fixed in the next commit, so adding an
error case didn't seem worth it. I'll do a better job foreshadowing.

>> The current behavior focuses on
>> pathspecs that match paths exactly. This includes exact filenames,
>> including directory names as prefixes. Pathspecs containing wildcards
>> or magic are cleared so the path walk downloads all blobs, as before.
> 
> Ah, "we punt and lift the limitation to grab everything, so at least
> everything you wanted to have will become available to you, even
> though we may download more than what you asked"?  OK, users would
> survive that, and as we improve the pathspec support, the user
> experience would only improve.  OK.

Exactly. I can word things better.

Thanks,
-Stolee