Merge branch 'sp/reflog' into next

* sp/reflog:
  Enable ref log creation in git checkout -b.
  Create/delete branch ref logs.
  Include ref log detail in commit, reset, etc.
  Change order of -m option to update-ref.
  Correct force_write bug in refs.c
  Change 'master@noon' syntax to 'master@{noon}'.
  Log ref updates made by fetch.
  Force writing ref if it doesn't exist.
  Added logs/ directory to repository layout.
  General ref log reading improvements.
  Fix ref log parsing so it works properly.
  Support 'master@2 hours ago' syntax
  Log ref updates to logs/refs/<ref>
  Convert update-ref to use ref_lock API.
  Improve abstraction of ref lock/write.

6 files changed, 67 insertions, 4 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d1a4bec0d4..e178ee2de1 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -70,6 +70,14 @@ core.preferSymlinkRefs::
 	This is sometimes needed to work with old scripts that
 	expect HEAD to be a symbolic link.
 
+core.logAllRefUpdates::
+	If true, `git-update-ref` will append a line to
+	"$GIT_DIR/logs/<ref>" listing the new SHA1 and the date/time
+	of the update.	If the file does not exist it will be
+	created automatically.	This information can be used to
+	determine what commit was the tip of a branch "2 days ago".
+	This value is false by default (no logging).
+
 core.repositoryFormatVersion::
 	Internal variable identifying the repository format and layout
 	version.
diff --git a/Documentation/git-branch.txt b/Documentation/git-branch.txt
index 0b37e2bfc8..d43ef1dec4 100644
--- a/Documentation/git-branch.txt
+++ b/Documentation/git-branch.txt
@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git-branch' [-r]
-'git-branch' [-f] <branchname> [<start-point>]
+'git-branch' [-l] [-f] <branchname> [<start-point>]
 'git-branch' (-d | -D) <branchname>...
 
 DESCRIPTION
@@ -23,7 +23,8 @@ If no <start-point> is given, the branch will be created with a head
 equal to that of the currently checked out branch.
 
 With a `-d` or `-D` option, `<branchname>` will be deleted.  You may
-specify more than one branch for deletion.
+specify more than one branch for deletion.  If the branch currently
+has a ref log then the ref log will also be deleted.
 
 
 OPTIONS
@@ -34,6 +35,11 @@ OPTIONS
 -D::
 	Delete a branch irrespective of its index status.
 
+-l::
+	Create the branch's ref log.  This activates recording of
+	all changes to made the branch ref, enabling use of date
+	based sha1 expressions such as "<branchname>@{yesterday}".
+
 -f::
 	Force the creation of a new branch even if it means deleting
 	a branch that already exists with the same name.
diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index d82efc00d4..fbdbadc74f 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -8,7 +8,7 @@ git-checkout - Checkout and switch to a branch
 SYNOPSIS
 --------
 [verse]
-'git-checkout' [-f] [-b <new_branch>] [-m] [<branch>]
+'git-checkout' [-f] [-b <new_branch> [-l]] [-m] [<branch>]
 'git-checkout' [-m] [<branch>] <paths>...
 
 DESCRIPTION
@@ -40,6 +40,11 @@ OPTIONS
 	by gitlink:git-check-ref-format[1].  Some of these checks
 	may restrict the characters allowed in a branch name.
 
+-l::
+	Create the new branch's ref log.  This activates recording of
+	all changes to made the branch ref, enabling use of date
+	based sha1 expressions such as "<branchname>@{yesterday}".
+
 -m::
 	If you have local modifications to one or more files that
 	are different between the current branch and the branch to
diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index ab896fcf83..b894694367 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -124,6 +124,13 @@ syntax.
   happen to have both heads/master and tags/master, you can
   explicitly say 'heads/master' to tell git which one you mean.
 
+* A suffix '@' followed by a date specification enclosed in a brace
+  pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1
+  second ago\}' or '\{1979-02-26 18:30:00\}') to specify the value
+  of the ref at a prior point in time.  This suffix may only be
+  used immediately following a ref name and the ref must have an
+  existing log ($GIT_DIR/logs/<ref>).
+
 * A suffix '{caret}' to a revision parameter means the first parent of
   that commit object.  '{caret}<n>' means the <n>th parent (i.e.
   'rev{caret}'
diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt
index 475237f19e..e062030e91 100644
--- a/Documentation/git-update-ref.txt
+++ b/Documentation/git-update-ref.txt
@@ -7,7 +7,7 @@ git-update-ref - update the object name stored in a ref safely
 
 SYNOPSIS
 --------
-'git-update-ref' <ref> <newvalue> [<oldvalue>]
+'git-update-ref' [-m <reason>] <ref> <newvalue> [<oldvalue>]
 
 DESCRIPTION
 -----------
@@ -49,6 +49,32 @@ for reading but not for writing (so we'll never write through a
 ref symlink to some other tree, if you have copied a whole
 archive by creating a symlink tree).
 
+Logging Updates
+---------------
+If config parameter "core.logAllRefUpdates" is true 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
++
+Where "oldsha1" is the 40 character hexadecimal value previously
+stored in <ref>, "newsha1" is the 40 character hexadecimal value of
+<newvalue> and "committer" is the committer's name, email address
+and date in the standard GIT committer ident format.
+
+Optionally with -m:
+
+    . oldsha1 SP newsha1 SP committer TAB message LF
++
+Where all fields are as described above and "message" is the
+value supplied to the -m option.
+
+An update will fail (without changing <ref>) if the current user is
+unable to create a new log file, append to the existing log file
+or does not have committer information available.
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>.
diff --git a/Documentation/repository-layout.txt b/Documentation/repository-layout.txt
index 98fbe7db52..b52dfdc308 100644
--- a/Documentation/repository-layout.txt
+++ b/Documentation/repository-layout.txt
@@ -128,3 +128,14 @@ remotes::
 	Stores shorthands to be used to give URL and default
 	refnames to interact with remote repository to `git
 	fetch`, `git pull` and `git push` commands.
+
+logs::
+	Records of changes made to refs are stored in this
+	directory.  See the documentation on git-update-ref
+	for more information.
+
+logs/refs/heads/`name`::
+	Records all changes made to the branch tip named `name`.
+
+logs/refs/tags/`name`::
+	Records all changes made to the tag named `name`.