merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 34 insertions, 7 deletions

diff --git a/third_party/git/Documentation/git-update-ref.txt b/third_party/git/Documentation/git-update-ref.txt
index 96714231179c..d401234b03ce 100644
--- a/third_party/git/Documentation/git-update-ref.txt
+++ b/third_party/git/Documentation/git-update-ref.txt
@@ -66,6 +66,10 @@ performs all modifications together.  Specify commands of the form:
 	delete SP <ref> [SP <oldvalue>] LF
 	verify SP <ref> [SP <oldvalue>] LF
 	option SP <opt> LF
+	start LF
+	prepare LF
+	commit LF
+	abort LF
 
 With `--create-reflog`, update-ref will create a reflog for each ref
 even if one would not ordinarily be created.
@@ -83,6 +87,10 @@ quoting:
 	delete SP <ref> NUL [<oldvalue>] NUL
 	verify SP <ref> NUL [<oldvalue>] NUL
 	option SP <opt> NUL
+	start NUL
+	prepare NUL
+	commit NUL
+	abort NUL
 
 In this format, use 40 "0" to specify a zero value, and use the empty
 string to specify a missing value.
@@ -107,13 +115,31 @@ delete::
 
 verify::
 	Verify <ref> against <oldvalue> but do not change it.  If
-	<oldvalue> zero or missing, the ref must not exist.
+	<oldvalue> is zero or missing, the ref must not exist.
 
 option::
 	Modify behavior of the next command naming a <ref>.
 	The only valid option is `no-deref` to avoid dereferencing
 	a symbolic ref.
 
+start::
+	Start a transaction. In contrast to a non-transactional session, a
+	transaction will automatically abort if the session ends without an
+	explicit commit.
+
+prepare::
+	Prepare to commit the transaction. This will create lock files for all
+	queued reference updates. If one reference could not be locked, the
+	transaction will be aborted.
+
+commit::
+	Commit all reference updates queued for the transaction, ending the
+	transaction.
+
+abort::
+	Abort the transaction, releasing all locks if the transaction is in
+	prepared state.
+
 If all <ref>s can be locked with matching <oldvalue>s
 simultaneously, all modifications are performed.  Otherwise, no
 modifications are performed.  Note that while each individual
@@ -122,12 +148,13 @@ still see a subset of the modifications.
 
 LOGGING UPDATES
 ---------------
-If config parameter "core.logAllRefUpdates" is true and the ref is one under
-"refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or
-the file "$GIT_DIR/logs/<ref>" exists then `git update-ref` will append
-a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all
-symbolic refs before creating the log name) describing the change
-in ref value.  Log lines are formatted as:
+If config parameter "core.logAllRefUpdates" is true and the ref is one
+under "refs/heads/", "refs/remotes/", "refs/notes/", or a pseudoref
+like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/<ref>" exists then
+`git update-ref` will append a line to the log file
+"$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating
+the log name) describing the change in ref value.  Log lines are
+formatted as:
 
     oldsha1 SP newsha1 SP committer LF