Merge branch 'bc/sha-256-part-3'

The final leg of SHA-256 transition.

* bc/sha-256-part-3: (39 commits)
  t: remove test_oid_init in tests
  docs: add documentation for extensions.objectFormat
  ci: run tests with SHA-256
  t: make SHA1 prerequisite depend on default hash
  t: allow testing different hash algorithms via environment
  t: add test_oid option to select hash algorithm
  repository: enable SHA-256 support by default
  setup: add support for reading extensions.objectformat
  bundle: add new version for use with SHA-256
  builtin/verify-pack: implement an --object-format option
  http-fetch: set up git directory before parsing pack hashes
  t0410: mark test with SHA1 prerequisite
  t5308: make test work with SHA-256
  t9700: make hash size independent
  t9500: ensure that algorithm info is preserved in config
  t9350: make hash size independent
  t9301: make hash size independent
  t9300: use $ZERO_OID instead of hard-coded object ID
  t9300: abstract away SHA-1-specific constants
  t8011: make hash size independent
  ...

4 files changed, 47 insertions, 2 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ef0768b91a..3042d80978 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -348,6 +348,8 @@ include::config/diff.txt[]
 
 include::config/difftool.txt[]
 
+include::config/extensions.txt[]
+
 include::config/fastimport.txt[]
 
 include::config/feature.txt[]
diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
new file mode 100644
index 0000000000..4e23d73cdc
--- /dev/null
+++ b/Documentation/config/extensions.txt
@@ -0,0 +1,8 @@
+extensions.objectFormat::
+	Specify the hash algorithm to use.  The acceptable values are `sha1` and
+	`sha256`.  If not specified, `sha1` is assumed.  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.
diff --git a/Documentation/git-bundle.txt b/Documentation/git-bundle.txt
index d34b0964be..53804cad4b 100644
--- a/Documentation/git-bundle.txt
+++ b/Documentation/git-bundle.txt
@@ -9,7 +9,8 @@ git-bundle - Move objects and refs by archive
 SYNOPSIS
 --------
 [verse]
-'git bundle' create [-q | --quiet | --progress | --all-progress] [--all-progress-implied] <file> <git-rev-list-args>
+'git bundle' create [-q | --quiet | --progress | --all-progress] [--all-progress-implied]
+		    [--version=<version>] <file> <git-rev-list-args>
 'git bundle' verify [-q | --quiet] <file>
 'git bundle' list-heads <file> [<refname>...]
 'git bundle' unbundle <file> [<refname>...]
@@ -102,6 +103,12 @@ unbundle <file>::
 	is activated.  Unlike --all-progress this flag doesn't actually
 	force any progress display by itself.
 
+--version=<version>::
+	Specify the bundle version.  Version 2 is the older format and can only be
+	used with SHA-1 repositories; the newer version 3 contains capabilities that
+	permit extensions. The default is the oldest supported format, based on the
+	hash algorithm in use.
+
 -q::
 --quiet::
 	This flag makes the command not to report its progress
diff --git a/Documentation/technical/bundle-format.txt b/Documentation/technical/bundle-format.txt
index 0e828151a5..bac558d049 100644
--- a/Documentation/technical/bundle-format.txt
+++ b/Documentation/technical/bundle-format.txt
@@ -7,6 +7,8 @@ The Git bundle format is a format that represents both refs and Git objects.
 We will use ABNF notation to define the Git bundle format. See
 protocol-common.txt for the details.
 
+A v2 bundle looks like this:
+
 ----
 bundle    = signature *prerequisite *reference LF pack
 signature = "# v2 git bundle" LF
@@ -18,9 +20,28 @@ reference    = obj-id SP refname LF
 pack         = ... ; packfile
 ----
 
+A v3 bundle looks like this:
+
+----
+bundle    = signature *capability *prerequisite *reference LF pack
+signature = "# v3 git bundle" LF
+
+capability   = "@" key ["=" value] LF
+prerequisite = "-" obj-id SP comment LF
+comment      = *CHAR
+reference    = obj-id SP refname LF
+key          = 1*(ALPHA / DIGIT / "-")
+value        = *(%01-09 / %0b-FF)
+
+pack         = ... ; packfile
+----
+
 == Semantics
 
-A Git bundle consists of three parts.
+A Git bundle consists of several parts.
+
+* "Capabilities", which are only in the v3 format, indicate functionality that
+	the bundle requires to be read properly.
 
 * "Prerequisites" lists the objects that are NOT included in the bundle and the
   reader of the bundle MUST already have, in order to use the data in the
@@ -46,3 +67,10 @@ put any string here. The reader of the bundle MUST ignore the comment.
 Note that the prerequisites does not represent a shallow-clone boundary. The
 semantics of the prerequisites and the shallow-clone boundaries are different,
 and the Git bundle v2 format cannot represent a shallow clone repository.
+
+== Capabilities
+
+Because there is no opportunity for negotiation, unknown capabilities cause 'git
+bundle' to abort.  The only known capability is `object-format`, which specifies
+the hash algorithm in use, and can take the same values as the
+`extensions.objectFormat` configuration value.