Merge branch 'tr/workflow-doc'

* tr/workflow-doc:
  Documentation: add manpage about workflows
  Documentation: Refer to git-rebase(1) to warn against rewriting
  Documentation: new upstream rebase recovery section in git-rebase

6 files changed, 500 insertions, 8 deletions

diff --git a/Documentation/Makefile b/Documentation/Makefile
index ded0e40b97..e33ddcb250 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -6,7 +6,7 @@ MAN5_TXT=gitattributes.txt gitignore.txt gitmodules.txt githooks.txt \
 	gitrepository-layout.txt
 MAN7_TXT=gitcli.txt gittutorial.txt gittutorial-2.txt \
 	gitcvs-migration.txt gitcore-tutorial.txt gitglossary.txt \
-	gitdiffcore.txt
+	gitdiffcore.txt gitworkflows.txt
 
 MAN_TXT = $(MAN1_TXT) $(MAN5_TXT) $(MAN7_TXT)
 MAN_XML=$(patsubst %.txt,%.xml,$(MAN_TXT))
diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index 41809eecab..2e62165fa9 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -145,6 +145,10 @@ It is a rough equivalent for:
 ------
 but can be used to amend a merge commit.
 --
++
+You should understand the implications of rewriting history if you
+amend a commit that has already been published.  (See the "RECOVERING
+FROM UPSTREAM REBASE" section in linkgit:git-rebase[1].)
 
 -i::
 --include::
diff --git a/Documentation/git-filter-branch.txt b/Documentation/git-filter-branch.txt
index b0e710d5f9..fed6de6a7f 100644
--- a/Documentation/git-filter-branch.txt
+++ b/Documentation/git-filter-branch.txt
@@ -36,7 +36,9 @@ the objects and will not converge with the original branch.  You will not
 be able to easily push and distribute the rewritten branch on top of the
 original branch.  Please do not use this command if you do not know the
 full implications, and avoid using it anyway, if a simple single commit
-would suffice to fix your problem.
+would suffice to fix your problem.  (See the "RECOVERING FROM UPSTREAM
+REBASE" section in linkgit:git-rebase[1] for further information about
+rewriting published history.)
 
 Always verify that the rewritten version is correct: The original refs,
 if different from the rewritten ones, will be stored in the namespace
diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index d639985693..c8ad86a56f 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -259,11 +259,10 @@ include::merge-strategies.txt[]
 
 NOTES
 -----
-When you rebase a branch, you are changing its history in a way that
-will cause problems for anyone who already has a copy of the branch
-in their repository and tries to pull updates from you.  You should
-understand the implications of using 'git-rebase' on a repository that
-you share.
+
+You should understand the implications of using 'git-rebase' on a
+repository that you share.  See also RECOVERING FROM UPSTREAM REBASE
+below.
 
 When the git-rebase command is run, it will first execute a "pre-rebase"
 hook if one exists.  You can use this hook to do sanity checks and
@@ -398,6 +397,127 @@ consistent (they compile, pass the testsuite, etc.) you should use
 after each commit, test, and amend the commit if fixes are necessary.
 
 
+RECOVERING FROM UPSTREAM REBASE
+-------------------------------
+
+Rebasing (or any other form of rewriting) a branch that others have
+based work on is a bad idea: anyone downstream of it is forced to
+manually fix their history.  This section explains how to do the fix
+from the downstream's point of view.  The real fix, however, would be
+to avoid rebasing the upstream in the first place.
+
+To illustrate, suppose you are in a situation where someone develops a
+'subsystem' branch, and you are working on a 'topic' that is dependent
+on this 'subsystem'.  You might end up with a history like the
+following:
+
+------------
+    o---o---o---o---o---o---o---o---o  master
+	 \
+	  o---o---o---o---o  subsystem
+			   \
+			    *---*---*  topic
+------------
+
+If 'subsystem' is rebased against 'master', the following happens:
+
+------------
+    o---o---o---o---o---o---o---o  master
+	 \			 \
+	  o---o---o---o---o	  o'--o'--o'--o'--o'  subsystem
+			   \
+			    *---*---*  topic
+------------
+
+If you now continue development as usual, and eventually merge 'topic'
+to 'subsystem', the commits from 'subsystem' will remain duplicated forever:
+
+------------
+    o---o---o---o---o---o---o---o  master
+	 \			 \
+	  o---o---o---o---o	  o'--o'--o'--o'--o'--M	 subsystem
+			   \			     /
+			    *---*---*-..........-*--*  topic
+------------
+
+Such duplicates are generally frowned upon because they clutter up
+history, making it harder to follow.  To clean things up, you need to
+transplant the commits on 'topic' to the new 'subsystem' tip, i.e.,
+rebase 'topic'.  This becomes a ripple effect: anyone downstream from
+'topic' is forced to rebase too, and so on!
+
+There are two kinds of fixes, discussed in the following subsections:
+
+Easy case: The changes are literally the same.::
+
+	This happens if the 'subsystem' rebase was a simple rebase and
+	had no conflicts.
+
+Hard case: The changes are not the same.::
+
+	This happens if the 'subsystem' rebase had conflicts, or used
+	`\--interactive` to omit, edit, or squash commits; or if the
+	upstream used one of `commit \--amend`, `reset`, or
+	`filter-branch`.
+
+
+The easy case
+~~~~~~~~~~~~~
+
+Only works if the changes (patch IDs based on the diff contents) on
+'subsystem' are literally the same before and after the rebase
+'subsystem' did.
+
+In that case, the fix is easy because 'git-rebase' knows to skip
+changes that are already present in the new upstream.  So if you say
+(assuming you're on 'topic')
+------------
+    $ git rebase subsystem
+------------
+you will end up with the fixed history
+------------
+    o---o---o---o---o---o---o---o  master
+				 \
+				  o'--o'--o'--o'--o'  subsystem
+						   \
+						    *---*---*  topic
+------------
+
+
+The hard case
+~~~~~~~~~~~~~
+
+Things get more complicated if the 'subsystem' changes do not exactly
+correspond to the ones before the rebase.
+
+NOTE: While an "easy case recovery" sometimes appears to be successful
+      even in the hard case, it may have unintended consequences.  For
+      example, a commit that was removed via `git rebase
+      \--interactive` will be **resurrected**!
+
+The idea is to manually tell 'git-rebase' "where the old 'subsystem'
+ended and your 'topic' began", that is, what the old merge-base
+between them was.  You will have to find a way to name the last commit
+of the old 'subsystem', for example:
+
+* With the 'subsystem' reflog: after 'git-fetch', the old tip of
+  'subsystem' is at `subsystem@\{1}`.  Subsequent fetches will
+  increase the number.  (See linkgit:git-reflog[1].)
+
+* Relative to the tip of 'topic': knowing that your 'topic' has three
+  commits, the old tip of 'subsystem' must be `topic~3`.
+
+You can then transplant the old `subsystem..topic` to the new tip by
+saying (for the reflog case, and assuming you are on 'topic' already):
+------------
+    $ git rebase --onto subsystem subsystem@{1}
+------------
+
+The ripple effect of a "hard case" recovery is especially bad:
+'everyone' downstream from 'topic' will now have to perform a "hard
+case" recovery too!
+
+
 Authors
 ------
 Written by Junio C Hamano <gitster@pobox.com> and
diff --git a/Documentation/git-reset.txt b/Documentation/git-reset.txt
index 6abaeac28c..52aab5e680 100644
--- a/Documentation/git-reset.txt
+++ b/Documentation/git-reset.txt
@@ -82,7 +82,9 @@ $ git reset --hard HEAD~3   <1>
 +
 <1> The last three commits (HEAD, HEAD^, and HEAD~2) were bad
 and you do not want to ever see them again.  Do *not* do this if
-you have already given these commits to somebody else.
+you have already given these commits to somebody else.  (See the
+"RECOVERING FROM UPSTREAM REBASE" section in linkgit:git-rebase[1] for
+the implications of doing so.)
 
 Undo a commit, making it a topic branch::
 +
diff --git a/Documentation/gitworkflows.txt b/Documentation/gitworkflows.txt
new file mode 100644
index 0000000000..7fe9f7295d
--- /dev/null
+++ b/Documentation/gitworkflows.txt
@@ -0,0 +1,364 @@
+gitworkflows(7)
+===============
+
+NAME
+----
+gitworkflows - An overview of recommended workflows with git
+
+SYNOPSIS
+--------
+git *
+
+
+DESCRIPTION
+-----------
+
+This document attempts to write down and motivate some of the workflow
+elements used for `git.git` itself.  Many ideas apply in general,
+though the full workflow is rarely required for smaller projects with
+fewer people involved.
+
+We formulate a set of 'rules' for quick reference, while the prose
+tries to motivate each of them.  Do not always take them literally;
+you should value good reasons for your actions higher than manpages
+such as this one.
+
+
+SEPARATE CHANGES
+----------------
+
+As a general rule, you should try to split your changes into small
+logical steps, and commit each of them.  They should be consistent,
+working independently of any later commits, pass the test suite, etc.
+This makes the review process much easier, and the history much more
+useful for later inspection and analysis, for example with
+linkgit:git-blame[1] and linkgit:git-bisect[1].
+
+To achieve this, try to split your work into small steps from the very
+beginning. It is always easier to squash a few commits together than
+to split one big commit into several.  Don't be afraid of making too
+small or imperfect steps along the way. You can always go back later
+and edit the commits with `git rebase \--interactive` before you
+publish them.  You can use `git stash save \--keep-index` to run the
+test suite independent of other uncommitted changes; see the EXAMPLES
+section of linkgit:git-stash[1].
+
+
+MANAGING BRANCHES
+-----------------
+
+There are two main tools that can be used to include changes from one
+branch on another: linkgit:git-merge[1] and
+linkgit:git-cherry-pick[1].
+
+Merges have many advantages, so we try to solve as many problems as
+possible with merges alone.  Cherry-picking is still occasionally
+useful; see "Merging upwards" below for an example.
+
+Most importantly, merging works at the branch level, while
+cherry-picking works at the commit level.  This means that a merge can
+carry over the changes from 1, 10, or 1000 commits with equal ease,
+which in turn means the workflow scales much better to a large number
+of contributors (and contributions).  Merges are also easier to
+understand because a merge commit is a "promise" that all changes from
+all its parents are now included.
+
+There is a tradeoff of course: merges require a more careful branch
+management.  The following subsections discuss the important points.
+
+
+Graduation
+~~~~~~~~~~
+
+As a given feature goes from experimental to stable, it also
+"graduates" between the corresponding branches of the software.
+`git.git` uses the following 'integration branches':
+
+* 'maint' tracks the commits that should go into the next "maintenance
+  release", i.e., update of the last released stable version;
+
+* 'master' tracks the commits that should go into the next release;
+
+* 'next' is intended as a testing branch for topics being tested for
+  stability for master.
+
+There is a fourth official branch that is used slightly differently:
+
+* 'pu' (proposed updates) is an integration branch for things that are
+  not quite ready for inclusion yet (see "Integration Branches"
+  below).
+
+Each of the four branches is usually a direct descendant of the one
+above it.
+
+Conceptually, the feature enters at an unstable branch (usually 'next'
+or 'pu'), and "graduates" to 'master' for the next release once it is
+considered stable enough.
+
+
+Merging upwards
+~~~~~~~~~~~~~~~
+
+The "downwards graduation" discussed above cannot be done by actually
+merging downwards, however, since that would merge 'all' changes on
+the unstable branch into the stable one.  Hence the following:
+
+.Merge upwards
+[caption="Rule: "]
+=====================================
+Always commit your fixes to the oldest supported branch that require
+them.  Then (periodically) merge the integration branches upwards into each
+other.
+=====================================
+
+This gives a very controlled flow of fixes.  If you notice that you
+have applied a fix to e.g. 'master' that is also required in 'maint',
+you will need to cherry-pick it (using linkgit:git-cherry-pick[1])
+downwards.  This will happen a few times and is nothing to worry about
+unless you do it very frequently.
+
+
+Topic branches
+~~~~~~~~~~~~~~
+
+Any nontrivial feature will require several patches to implement, and
+may get extra bugfixes or improvements during its lifetime.
+
+Committing everything directly on the integration branches leads to many
+problems: Bad commits cannot be undone, so they must be reverted one
+by one, which creates confusing histories and further error potential
+when you forget to revert part of a group of changes.  Working in
+parallel mixes up the changes, creating further confusion.
+
+Use of "topic branches" solves these problems.  The name is pretty
+self explanatory, with a caveat that comes from the "merge upwards"
+rule above:
+
+.Topic branches
+[caption="Rule: "]
+=====================================
+Make a side branch for every topic (feature, bugfix, ...). Fork it off
+at the oldest integration branch that you will eventually want to merge it
+into.
+=====================================
+
+Many things can then be done very naturally:
+
+* To get the feature/bugfix into an integration branch, simply merge
+  it.  If the topic has evolved further in the meantime, merge again.
+  (Note that you do not necessarily have to merge it to the oldest
+  integration branch first.  For example, you can first merge a bugfix
+  to 'next', give it some testing time, and merge to 'maint' when you
+  know it is stable.)
+
+* If you find you need new features from the branch 'other' to continue
+  working on your topic, merge 'other' to 'topic'.  (However, do not
+  do this "just habitually", see below.)
+
+* If you find you forked off the wrong branch and want to move it
+  "back in time", use linkgit:git-rebase[1].
+
+Note that the last point clashes with the other two: a topic that has
+been merged elsewhere should not be rebased.  See the section on
+RECOVERING FROM UPSTREAM REBASE in linkgit:git-rebase[1].
+
+We should point out that "habitually" (regularly for no real reason)
+merging an integration branch into your topics -- and by extension,
+merging anything upstream into anything downstream on a regular basis
+-- is frowned upon:
+
+.Merge to downstream only at well-defined points
+[caption="Rule: "]
+=====================================
+Do not merge to downstream except with a good reason: upstream API
+changes affect your branch; your branch no longer merges to upstream
+cleanly; etc.
+=====================================
+
+Otherwise, the topic that was merged to suddenly contains more than a
+single (well-separated) change.  The many resulting small merges will
+greatly clutter up history.  Anyone who later investigates the history
+of a file will have to find out whether that merge affected the topic
+in development.  An upstream might even inadvertently be merged into a
+"more stable" branch.  And so on.
+
+
+Throw-away integration
+~~~~~~~~~~~~~~~~~~~~~~
+
+If you followed the last paragraph, you will now have many small topic
+branches, and occasionally wonder how they interact.  Perhaps the
+result of merging them does not even work?  But on the other hand, we
+want to avoid merging them anywhere "stable" because such merges
+cannot easily be undone.
+
+The solution, of course, is to make a merge that we can undo: merge
+into a throw-away branch.
+
+.Throw-away integration branches
+[caption="Rule: "]
+=====================================
+To test the interaction of several topics, merge them into a
+throw-away branch.  You must never base any work on such a branch!
+=====================================
+
+If you make it (very) clear that this branch is going to be deleted
+right after the testing, you can even publish this branch, for example
+to give the testers a chance to work with it, or other developers a
+chance to see if their in-progress work will be compatible.  `git.git`
+has such an official throw-away integration branch called 'pu'.
+
+
+DISTRIBUTED WORKFLOWS
+---------------------
+
+After the last section, you should know how to manage topics.  In
+general, you will not be the only person working on the project, so
+you will have to share your work.
+
+Roughly speaking, there are two important workflows: merge and patch.
+The important difference is that the merge workflow can propagate full
+history, including merges, while patches cannot.  Both workflows can
+be used in parallel: in `git.git`, only subsystem maintainers use
+the merge workflow, while everyone else sends patches.
+
+Note that the maintainer(s) may impose restrictions, such as
+"Signed-off-by" requirements, that all commits/patches submitted for
+inclusion must adhere to.  Consult your project's documentation for
+more information.
+
+
+Merge workflow
+~~~~~~~~~~~~~~
+
+The merge workflow works by copying branches between upstream and
+downstream.  Upstream can merge contributions into the official
+history; downstream base their work on the official history.
+
+There are three main tools that can be used for this:
+
+* linkgit:git-push[1] copies your branches to a remote repository,
+  usually to one that can be read by all involved parties;
+
+* linkgit:git-fetch[1] that copies remote branches to your repository;
+  and
+
+* linkgit:git-pull[1] that does fetch and merge in one go.
+
+Note the last point.  Do 'not' use 'git-pull' unless you actually want
+to merge the remote branch.
+
+Getting changes out is easy:
+
+.Push/pull: Publishing branches/topics
+[caption="Recipe: "]
+=====================================
+`git push <remote> <branch>` and tell everyone where they can fetch
+from.
+=====================================
+
+You will still have to tell people by other means, such as mail.  (Git
+provides the linkgit:request-pull[1] to send preformatted pull
+requests to upstream maintainers to simplify this task.)
+
+If you just want to get the newest copies of the integration branches,
+staying up to date is easy too:
+
+.Push/pull: Staying up to date
+[caption="Recipe: "]
+=====================================
+Use `git fetch <remote>` or `git remote update` to stay up to date.
+=====================================
+
+Then simply fork your topic branches from the stable remotes as
+explained earlier.
+
+If you are a maintainer and would like to merge other people's topic
+branches to the integration branches, they will typically send a
+request to do so by mail.  Such a request looks like
+
+-------------------------------------
+Please pull from
+    <url> <branch>
+-------------------------------------
+
+In that case, 'git-pull' can do the fetch and merge in one go, as
+follows.
+
+.Push/pull: Merging remote topics
+[caption="Recipe: "]
+=====================================
+`git pull <url> <branch>`
+=====================================
+
+Occasionally, the maintainer may get merge conflicts when he tries to
+pull changes from downstream.  In this case, he can ask downstream to
+do the merge and resolve the conflicts themselves (perhaps they will
+know better how to resolve them).  It is one of the rare cases where
+downstream 'should' merge from upstream.
+
+
+Patch workflow
+~~~~~~~~~~~~~~
+
+If you are a contributor that sends changes upstream in the form of
+emails, you should use topic branches as usual (see above).  Then use
+linkgit:git-format-patch[1] to generate the corresponding emails
+(highly recommended over manually formatting them because it makes the
+maintainer's life easier).
+
+.format-patch/am: Publishing branches/topics
+[caption="Recipe: "]
+=====================================
+* `git format-patch -M upstream..topic` to turn them into preformatted
+  patch files
+* `git send-email --to=<recipient> <patches>`
+=====================================
+
+See the linkgit:git-format-patch[1] and linkgit:git-send-email[1]
+manpages for further usage notes.
+
+If the maintainer tells you that your patch no longer applies to the
+current upstream, you will have to rebase your topic (you cannot use a
+merge because you cannot format-patch merges):
+
+.format-patch/am: Keeping topics up to date
+[caption="Recipe: "]
+=====================================
+`git pull --rebase <url> <branch>`
+=====================================
+
+You can then fix the conflicts during the rebase.  Presumably you have
+not published your topic other than by mail, so rebasing it is not a
+problem.
+
+If you receive such a patch series (as maintainer, or perhaps as a
+reader of the mailing list it was sent to), save the mails to files,
+create a new topic branch and use 'git-am' to import the commits:
+
+.format-patch/am: Importing patches
+[caption="Recipe: "]
+=====================================
+`git am < patch`
+=====================================
+
+One feature worth pointing out is the three-way merge, which can help
+if you get conflicts: `git am -3` will use index information contained
+in patches to figure out the merge base.  See linkgit:git-am[1] for
+other options.
+
+
+SEE ALSO
+--------
+linkgit:gittutorial[7],
+linkgit:git-push[1],
+linkgit:git-pull[1],
+linkgit:git-merge[1],
+linkgit:git-rebase[1],
+linkgit:git-format-patch[1],
+linkgit:git-send-email[1],
+linkgit:git-am[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite.