Merge branch 'jx/proc-receive-hook'

"git receive-pack" that accepts requests by "git push" learned to
outsource most of the ref updates to the new "proc-receive" hook.

* jx/proc-receive-hook:
  doc: add documentation for the proc-receive hook
  transport: parse report options for tracking refs
  t5411: test updates of remote-tracking branches
  receive-pack: new config receive.procReceiveRefs
  doc: add document for capability report-status-v2
  New capability "report-status-v2" for git-push
  receive-pack: feed report options to post-receive
  receive-pack: add new proc-receive hook
  t5411: add basic test cases for proc-receive hook
  transport: not report a non-head push as a branch

4 files changed, 136 insertions, 6 deletions

diff --git a/Documentation/config/receive.txt b/Documentation/config/receive.txt
index 65f78aac37..85d5b5a3d2 100644
--- a/Documentation/config/receive.txt
+++ b/Documentation/config/receive.txt
@@ -114,6 +114,28 @@ receive.hideRefs::
 	An attempt to update or delete a hidden ref by `git push` is
 	rejected.
 
+receive.procReceiveRefs::
+	This is a multi-valued variable that defines reference prefixes
+	to match the commands in `receive-pack`.  Commands matching the
+	prefixes will be executed by an external hook "proc-receive",
+	instead of the internal `execute_commands` function.  If this
+	variable is not defined, the "proc-receive" hook will never be
+	used, and all commands will be executed by the internal
+	`execute_commands` function.
++
+For example, if this variable is set to "refs/for", pushing to reference
+such as "refs/for/master" will not create or update a reference named
+"refs/for/master", but may create or update a pull request directly by
+running the hook "proc-receive".
++
+Optional modifiers can be provided in the beginning of the value to filter
+commands for specific actions: create (a), modify (m), delete (d).
+A `!` can be included in the modifiers to negate the reference prefix entry.
+E.g.:
++
+	git config --system --add receive.procReceiveRefs ad:refs/heads
+	git config --system --add receive.procReceiveRefs !:refs/heads
+
 receive.updateServerInfo::
 	If set to true, git-receive-pack will run git-update-server-info
 	after receiving data from git-push and updating refs.
diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index cf95d6d02b..6e461ace6e 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -335,6 +335,68 @@ The default 'update' hook, when enabled--and with
 `hooks.allowunannotated` config option unset or set to false--prevents
 unannotated tags to be pushed.
 
+[[proc-receive]]
+proc-receive
+~~~~~~~~~~~~
+
+This hook is invoked by linkgit:git-receive-pack[1].  If the server has
+set the multi-valued config variable `receive.procReceiveRefs`, and the
+commands sent to 'receive-pack' have matching reference names, these
+commands will be executed by this hook, instead of by the internal
+`execute_commands()` function.  This hook is responsible for updating
+the relevant references and reporting the results back to 'receive-pack'.
+
+This hook executes once for the receive operation.  It takes no
+arguments, but uses a pkt-line format protocol to communicate with
+'receive-pack' to read commands, push-options and send results.  In the
+following example for the protocol, the letter 'S' stands for
+'receive-pack' and the letter 'H' stands for this hook.
+
+    # Version and features negotiation.
+    S: PKT-LINE(version=1\0push-options atomic...)
+    S: flush-pkt
+    H: PKT-LINE(version=1\0push-options...)
+    H: flush-pkt
+
+    # Send commands from server to the hook.
+    S: PKT-LINE(<old-oid> <new-oid> <ref>)
+    S: ... ...
+    S: flush-pkt
+    # Send push-options only if the 'push-options' feature is enabled.
+    S: PKT-LINE(push-option)
+    S: ... ...
+    S: flush-pkt
+
+    # Receive result from the hook.
+    # OK, run this command successfully.
+    H: PKT-LINE(ok <ref>)
+    # NO, I reject it.
+    H: PKT-LINE(ng <ref> <reason>)
+    # Fall through, let 'receive-pack' to execute it.
+    H: PKT-LINE(ok <ref>)
+    H: PKT-LINE(option fall-through)
+    # OK, but has an alternate reference.  The alternate reference name
+    # and other status can be given in option directives.
+    H: PKT-LINE(ok <ref>)
+    H: PKT-LINE(option refname <refname>)
+    H: PKT-LINE(option old-oid <old-oid>)
+    H: PKT-LINE(option new-oid <new-oid>)
+    H: PKT-LINE(option forced-update)
+    H: ... ...
+    H: flush-pkt
+
+Each command for the 'proc-receive' hook may point to a pseudo-reference
+and always has a zero-old as its old-oid, while the 'proc-receive' hook
+may update an alternate reference and the alternate reference may exist
+already with a non-zero old-oid.  For this case, this hook will use
+"option" directives to report extended attributes for the reference given
+by the leading "ok" directive.
+
+The report of the commands of this hook should have the same order as
+the input.  The exit status of the 'proc-receive' hook only determines
+the success or failure of the group of commands sent to it, unless
+atomic push is in use.
+
 [[post-receive]]
 post-receive
 ~~~~~~~~~~~~
diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index a4573d12ce..e13a2c064d 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -503,8 +503,8 @@ The reference discovery phase is done nearly the same way as it is in the
 fetching protocol. Each reference obj-id and name on the server is sent
 in packet-line format to the client, followed by a flush-pkt.  The only
 real difference is that the capability listing is different - the only
-possible values are 'report-status', 'delete-refs', 'ofs-delta' and
-'push-options'.
+possible values are 'report-status', 'report-status-v2', 'delete-refs',
+'ofs-delta', 'atomic' and 'push-options'.
 
 Reference Update Request and Packfile Transfer
 ----------------------------------------------
@@ -625,7 +625,7 @@ Report Status
 -------------
 
 After receiving the pack data from the sender, the receiver sends a
-report if 'report-status' capability is in effect.
+report if 'report-status' or 'report-status-v2' capability is in effect.
 It is a short listing of what happened in that update.  It will first
 list the status of the packfile unpacking as either 'unpack ok' or
 'unpack [error]'.  Then it will list the status for each of the references
@@ -647,6 +647,41 @@ update was successful, or 'ng [refname] [error]' if the update was not.
   error-msg         = 1*(OCTET) ; where not "ok"
 ----
 
+The 'report-status-v2' capability extends the protocol by adding new option
+lines in order to support reporting of reference rewritten by the
+'proc-receive' hook.  The 'proc-receive' hook may handle a command for a
+pseudo-reference which may create or update one or more references, and each
+reference may have different name, different new-oid, and different old-oid.
+
+----
+  report-status-v2  = unpack-status
+		      1*(command-status-v2)
+		      flush-pkt
+
+  unpack-status     = PKT-LINE("unpack" SP unpack-result)
+  unpack-result     = "ok" / error-msg
+
+  command-status-v2 = command-ok-v2 / command-fail
+  command-ok-v2     = command-ok
+		      *option-line
+
+  command-ok        = PKT-LINE("ok" SP refname)
+  command-fail      = PKT-LINE("ng" SP refname SP error-msg)
+
+  error-msg         = 1*(OCTET) ; where not "ok"
+
+  option-line       = *1(option-refname)
+		      *1(option-old-oid)
+		      *1(option-new-oid)
+		      *1(option-forced-update)
+
+  option-refname    = PKT-LINE("option" SP "refname" SP refname)
+  option-old-oid    = PKT-LINE("option" SP "old-oid" SP obj-id)
+  option-new-oid    = PKT-LINE("option" SP "new-oid" SP obj-id)
+  option-force      = PKT-LINE("option" SP "forced-update")
+
+----
+
 Updates can be unsuccessful for a number of reasons.  The reference can have
 changed since the reference discovery phase was originally sent, meaning
 someone pushed in the meantime.  The reference being pushed could be a
diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index 124d716807..ba869a7d36 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -22,9 +22,9 @@ was sent.  Server MUST NOT ignore capabilities that client requested
 and server advertised.  As a consequence of these rules, server MUST
 NOT advertise capabilities it does not understand.
 
-The 'atomic', 'report-status', 'delete-refs', 'quiet', and 'push-cert'
-capabilities are sent and recognized by the receive-pack (push to server)
-process.
+The 'atomic', 'report-status', 'report-status-v2', 'delete-refs', 'quiet',
+and 'push-cert' capabilities are sent and recognized by the receive-pack
+(push to server) process.
 
 The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized
 by both upload-pack and receive-pack protocols.  The 'agent' capability
@@ -284,6 +284,17 @@ each reference was updated successfully.  If any of those were not
 successful, it will send back an error message.  See pack-protocol.txt
 for example messages.
 
+report-status-v2
+----------------
+
+Capability 'report-status-v2' extends capability 'report-status' by
+adding new "option" directives in order to support reference rewritten by
+the "proc-receive" hook.  The "proc-receive" hook may handle a command
+for a pseudo-reference which may create or update a reference with
+different name, new-oid, and old-oid.  While the capability
+'report-status' cannot report for such case.  See pack-protocol.txt
+for details.
+
 delete-refs
 -----------