Re: [PATCH 5/5] path-walk: support wildcard pathspecs for blob filtering

[Junio C Hamano <gitster@pobox.com>]

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <stolee@gmail.com>
>
> Previously, walk_objects_by_path() silently ignored pathspecs containing
> wildcards or magic by clearing them. This caused all blobs to be
> downloaded regardless of the given pathspec. Wildcard pathspecs like
> "d/file.*.txt" are useful for narrowing which blobs to process (e.g.,
> during 'git backfill').
>
> Support wildcard pathspecs by making three changes:
>
>  1. Add an 'exact_pathspecs' flag to path_walk_context. When the
>     pathspec has no wildcards or magic, set this flag and use the
>     existing fast-path prefix matching in add_tree_entries(). When
>     wildcards are present, skip that block since prefix matching
>     cannot handle glob patterns.
>
>  2. Disable revision-level commit pruning (revs->prune = 0) for
>     wildcard pathspecs. The revision walk uses the pathspec to filter
>     commits via TREESAME detection. For exact prefix pathspecs this
>     works well, but wildcard pathspecs may fail to match through
>     TREESAME because fnmatch with WM_PATHNAME does not cross directory
>     boundaries. Disabling pruning ensures all commits are visited and
>     their trees are available for the path-walk to filter.

Hmph, I wonder how significant an impact does it have on the
performance that we have to disable pruning here.  With the bog
standard tree traversal, wouldn't tree_entry_interesting() already
be capable of doing this, even with fnmatch / WM_PATHNAME ?

>  3. Add a match_pathspec() check in walk_path() to filter out blobs
>     whose full path does not match the pathspec. This provides the
>     actual blob-level filtering for wildcard pathspecs.
>
> Signed-off-by: Derrick Stolee <stolee@gmail.com>
> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The latter person cannot sign DCO or vouch for the origin of what
they have written in this patch, can they?

> ---
>  path-walk.c         | 22 ++++++++++++++--------
>  t/t5620-backfill.sh |  7 +++----
>  2 files changed, 17 insertions(+), 12 deletions(-)