Merge branch 'tb/repack-write-midx'

"git repack" has been taught to generate multi-pack reachability
bitmaps.

* tb/repack-write-midx:
  test-read-midx: fix leak of bitmap_index struct
  builtin/repack.c: pass `--refs-snapshot` when writing bitmaps
  builtin/repack.c: make largest pack preferred
  builtin/repack.c: support writing a MIDX while repacking
  builtin/repack.c: extract showing progress to a variable
  builtin/repack.c: rename variables that deal with non-kept packs
  builtin/repack.c: keep track of existing packs unconditionally
  midx: preliminary support for `--refs-snapshot`
  builtin/multi-pack-index.c: support `--stdin-packs` mode
  midx: expose `write_midx_file_only()` publicly

Documentation/git-multi-pack-index.txt

@@ -45,6 +45,25 @@ write::
 
 	--[no-]bitmap::
 		Control whether or not a multi-pack bitmap is written.
+
+	--stdin-packs::
+		Write a multi-pack index containing only the set of
+		line-delimited pack index basenames provided over stdin.
+
+	--refs-snapshot=<path>::
+		With `--bitmap`, optionally specify a file which
+		contains a "refs snapshot" taken prior to repacking.
++
+A reference snapshot is composed of line-delimited OIDs corresponding to
+the reference tips, usually taken by `git repack` prior to generating a
+new pack. A line may optionally start with a `+` character to indicate
+that the reference which corresponds to that OID is "preferred" (see
+linkgit:git-config[1]'s `pack.preferBitmapTips`.)
++
+The file given at `<path>` is expected to be readable, and can contain
+duplicates. (If a given OID is given more than once, it is marked as
+preferred if at least one instance of it begins with the special `+`
+marker).
 --
 
 verify::

Documentation/git-repack.txt

@@ -9,7 +9,7 @@ git-repack - Pack unpacked objects in a repository
 SYNOPSIS
 --------
 [verse]
-'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]
+'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m] [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>] [--write-midx]
 
 DESCRIPTION
 -----------
@@ -128,10 +128,11 @@ depth is 4095.
 -b::
 --write-bitmap-index::
 	Write a reachability bitmap index as part of the repack. This
-	only makes sense when used with `-a` or `-A`, as the bitmaps
+	only makes sense when used with `-a`, `-A` or `-m`, as the bitmaps
 	must be able to refer to all reachable objects. This option
-	overrides the setting of `repack.writeBitmaps`.  This option
-	has no effect if multiple packfiles are created.
+	overrides the setting of `repack.writeBitmaps`. This option
+	has no effect if multiple packfiles are created, unless writing a
+	MIDX (in which case a multi-pack bitmap is created).
 
 --pack-kept-objects::
 	Include objects in `.keep` files when repacking.  Note that we
@@ -189,6 +190,15 @@ this "roll-up", without respect to their reachability. This is subject
 to change in the future. This option (implying a drastically different
 repack mode) is not guaranteed to work with all other combinations of
 option to `git repack`.
++
+When writing a multi-pack bitmap, `git repack` selects the largest resulting
+pack as the preferred pack for object selection by the MIDX (see
+linkgit:git-multi-pack-index[1]).
+
+-m::
+--write-midx::
+	Write a multi-pack index (see linkgit:git-multi-pack-index[1])
+	containing the non-redundant packs.
 
 CONFIGURATION
 -------------