Merge branch 'ps/refstorage-extension'

Introduce a new extension "refstorage" so that we can mark a
repository that uses a non-default ref backend, like reftable.

* ps/refstorage-extension:
  t9500: write "extensions.refstorage" into config
  builtin/clone: introduce `--ref-format=` value flag
  builtin/init: introduce `--ref-format=` value flag
  builtin/rev-parse: introduce `--show-ref-format` flag
  t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
  setup: introduce GIT_DEFAULT_REF_FORMAT envvar
  setup: introduce "extensions.refStorage" extension
  setup: set repository's formats on init
  setup: start tracking ref storage format
  refs: refactor logic to look up storage backends
  worktree: skip reading HEAD when repairing worktrees
  t: introduce DEFAULT_REPO_FORMAT prereq

7 files changed, 38 insertions, 0 deletions

diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
index bccaec7a96..66db0e15da 100644
--- a/Documentation/config/extensions.txt
+++ b/Documentation/config/extensions.txt
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index c37c4a37f7..6e43eb9c20 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.
diff --git a/Documentation/git-init.txt b/Documentation/git-init.txt
index 6f0d2973bf..e8dc645bb5 100644
--- a/Documentation/git-init.txt
+++ b/Documentation/git-init.txt
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 
@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE
diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 912fab9f5e..546faf9017 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 962887f190..da4e8d1303 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::
diff --git a/Documentation/ref-storage-format.txt b/Documentation/ref-storage-format.txt
new file mode 100644
index 0000000000..1a65cac468
--- /dev/null
+++ b/Documentation/ref-storage-format.txt
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.
diff --git a/Documentation/technical/repository-version.txt b/Documentation/technical/repository-version.txt
index 045a76756f..27be3741e6 100644
--- a/Documentation/technical/repository-version.txt
+++ b/Documentation/technical/repository-version.txt
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).