[GSoC PATCH v4 7/7] Documentation/git-repack: document --drop-filtered and --dry-run

Describe the new --drop-filtered and --dry-run options: what they do,
only blob:limit filters are supported for now, a promisor remote is
required, --drop-filtered requires -a and implies -d so the redundant
packs are actually removed, its incompatibilities with --filter-to and
bitmap writing, and the safety guards that refuse to run mid-operation
or to drop index-referenced blobs.

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Siddharth Asthana <[email protected]>
Signed-off-by: Siddharth Shrimali <[email protected]>
---
 Documentation/git-repack.adoc | 37 +++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Documentation/git-repack.adoc b/Documentation/git-repack.adoc
index 72c42015e2..63943b078c 100644
--- a/Documentation/git-repack.adoc
+++ b/Documentation/git-repack.adoc
@@ -12,6 +12,7 @@ SYNOPSIS
 'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m]
 	[--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]
 	[--write-midx[=<mode>]] [--name-hash-version=<n>] [--path-walk]
+	[--filter=<filter-spec>] [--drop-filtered [--dry-run]]
 
 DESCRIPTION
 -----------
@@ -182,6 +183,42 @@ depth is 4095.
 	`objects` and `objects/info/alternates` sections of
 	linkgit:gitrepository-layout[5].
 
+--drop-filtered::
+	Delete the local objects that match the `--filter` specification
+	instead of keeping them in a separate packfile, reclaiming the
+	disk space they occupy. This is intended for partial clones,
+	where the filtered objects are promisor objects that remain
+	recoverable from the promisor remote and are lazily re-fetched
+	on demand when they are next needed.
++
+Only large blobs are supported for now, so `--filter=blob:limit=<n>`
+is currently the only accepted filter. Because dropped objects must be
+recoverable, this option requires a promisor remote to be configured
+and refuses to run otherwise.
++
+This option requires `-a`, and implies `-d`: the objects are dropped by
+rebuilding the promisor pack without them and then removing the now
+redundant old packs, so the redundant packs must be deleted for the
+space to actually be reclaimed. It is incompatible with `--filter-to`
+and with bitmap writing (`-b`/`--write-bitmap-index`), since filtering
+breaks the single-pack closure that bitmaps require. A bitmap setting
+coming from configuration is silently disabled for the duration of the
+command.
++
+As a convenience since dropped objects remain recoverable by lazy fetch,
+`--drop-filtered` refuses to run while another operation
+(merge, rebase, am, cherry-pick, revert, or bisect) is in progress, to
+avoid a surprising network fetch mid-operation, and refuses to drop any
+blob that the current index references, since such a blob would only be
+lazily re-fetched by the next command that inspects the working tree.
+These checks are skipped in bare repositories, which have neither a
+working tree nor an index.
+
+--dry-run::
+	Only meaningful with `--drop-filtered`. List the objects that
+	would be dropped, one object ID per line, without rebuilding any
+	pack or deleting anything.
+
 -b::
 --write-bitmap-index::
 	Write a reachability bitmap index as part of the repack. This
-- 
2.54.0