Merge branch 'jc/better-conflict-resolution'

* jc/better-conflict-resolution:
  Fix AsciiDoc errors in merge documentation
  git-merge documentation: describe how conflict is presented
  checkout --conflict=<style>: recreate merge in a non-default style
  checkout -m: recreate merge when checking out of unmerged index
  git-merge-recursive: learn to honor merge.conflictstyle
  merge.conflictstyle: choose between "merge" and "diff3 -m" styles
  rerere: understand "diff3 -m" style conflicts with the original
  rerere.c: use symbolic constants to keep track of parsing states
  xmerge.c: "diff3 -m" style clips merge reduction level to EAGER or less
  xmerge.c: minimum readability fixups
  xdiff-merge: optionally show conflicts in "diff3 -m" style
  xdl_fill_merge_buffer(): separate out a too deeply nested function
  checkout --ours/--theirs: allow checking out one side of a conflicting merge
  checkout -f: allow ignoring unmerged paths when checking out of the index

Conflicts:
	Documentation/git-checkout.txt
	builtin-checkout.c
	builtin-merge-recursive.c
	t/t7201-co.sh

3 files changed, 107 insertions, 7 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 1f805b2ec..bbe38ccaa 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -927,6 +927,14 @@ man.<tool>.path::
 	Override the path for the given tool that may be used to
 	display help in the 'man' format. See linkgit:git-help[1].
 
+merge.conflictstyle::
+	Specify the style in which conflicted hunks are written out to
+	working tree files upon merge.  The default is "merge", which
+	shows `<<<<<<<` conflict marker, change made by one side,
+	`=======` marker, change made by the other side, and then
+	`>>>>>>>` marker.  An alternate style, "diff3", adds `|||||||`
+	marker and the original text before `=======` marker.
+
 mergetool.<tool>.path::
 	Override the path for the given tool.  This is useful in case
 	your tool is not in the PATH.
diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index be54a0299..82e154de4 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git checkout' [-q] [-f] [--track | --no-track] [-b <new_branch> [-l]] [-m] [<branch>]
-'git checkout' [<tree-ish>] [--] <paths>...
+'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>...
 
 DESCRIPTION
 -----------
@@ -27,14 +27,20 @@ the first namespace level.
 
 When <paths> are given, this command does *not* switch
 branches.  It updates the named paths in the working tree from
-the index file (i.e. it runs `git checkout-index -f -u`), or
-from a named commit.  In
-this case, the `-f` and `-b` options are meaningless and giving
+the index file, or from a named commit.  In
+this case, the `-b` options is meaningless and giving
 either of them results in an error.  <tree-ish> argument can be
 used to specify a specific tree-ish (i.e. commit, tag or tree)
 to update the index for the given paths before updating the
 working tree.
 
+The index may contain unmerged entries after a failed merge.  By
+default, if you try to check out such an entry from the index, the
+checkout operation will fail and nothing will be checked out.
+Using -f will ignore these unmerged entries.  The contents from a
+specific side of the merge can be checked out of the index by
+using --ours or --theirs.  With -m, changes made to the working tree
+file can be discarded to recreate the original conflicted merge result.
 
 OPTIONS
 -------
@@ -42,8 +48,17 @@ OPTIONS
 	Quiet, suppress feedback messages.
 
 -f::
-	Proceed even if the index or the working tree differs
-	from HEAD.  This is used to throw away local changes.
+	When switching branches, proceed even if the index or the
+	working tree differs from HEAD.  This is used to throw away
+	local changes.
++
+When checking out paths from the index, do not fail upon unmerged
+entries; instead, unmerged entries are ignored.
+
+--ours::
+--theirs::
+	When checking out paths from the index, check out stage #2
+	('ours') or #3 ('theirs') for unmerged paths.
 
 -b::
 	Create a new branch named <new_branch> and start it at
@@ -84,7 +99,9 @@ exlicitly give a name with '-b' in such a case.
 	based sha1 expressions such as "<branchname>@\{yesterday}".
 
 -m::
-	If you have local modifications to one or more files that
+--merge::
+	When switching branches,
+	if you have local modifications to one or more files that
 	are different between the current branch and the branch to
 	which you are switching, the command refuses to switch
 	branches in order to preserve your modifications in context.
@@ -96,6 +113,16 @@ When a merge conflict happens, the index entries for conflicting
 paths are left unmerged, and you need to resolve the conflicts
 and mark the resolved paths with `git add` (or `git rm` if the merge
 should result in deletion of the path).
++
+When checking out paths from the index, this option lets you recreate
+the conflicted merge in the specified paths.
+
+--conflict=<style>::
+	The same as --merge option above, but changes the way the
+	conflicting hunks are presented, overriding the
+	merge.conflictstyle configuration variable.  Possible values are
+	"merge" (default) and "diff3" (in addition to what is shown by
+	"merge" style, shows the original contents).
 
 <new_branch>::
 	Name for the new branch.
diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt
index 685e1fed5..1f30830d4 100644
--- a/Documentation/git-merge.txt
+++ b/Documentation/git-merge.txt
@@ -119,6 +119,71 @@ When there are conflicts, these things happen:
    same and the index entries for them stay as they were,
    i.e. matching `HEAD`.
 
+HOW CONFLICTS ARE PRESENTED
+---------------------------
+
+During a merge, the working tree files are updated to reflect the result
+of the merge.  Among the changes made to the common ancestor's version,
+non-overlapping ones (that is, you changed an area of the file while the
+other side left that area intact, or vice versa) are incorporated in the
+final result verbatim.  When both sides made changes to the same area,
+however, git cannot randomly pick one side over the other, and asks you to
+resolve it by leaving what both sides did to that area.
+
+By default, git uses the same style as that is used by "merge" program
+from the RCS suite to present such a conflicted hunk, like this:
+
+------------
+Here are lines that are either unchanged from the common
+ancestor, or cleanly resolved because only one side changed.
+<<<<<<< yours:sample.txt
+Conflict resolution is hard;
+let's go shopping.
+=======
+Git makes conflict resolution easy.
+>>>>>>> theirs:sample.txt
+And here is another line that is cleanly resolved or unmodified.
+------------
+
+The area a pair of conflicting changes happened is marked with markers
+"`<<<<<<<`", "`=======`", and "`>>>>>>>`".  The part before the "`=======`"
+is typically your side, and the part after it is typically their side.
+
+The default format does not show what the original said in the conflicted
+area.  You cannot tell how many lines are deleted and replaced with the
+Barbie's remark by your side.  The only thing you can tell is that your
+side wants to say it is hard and you'd prefer to go shopping, while the
+other side wants to claim it is easy.
+
+An alternative style can be used by setting the "merge.conflictstyle"
+configuration variable to "diff3".  In "diff3" style, the above conflict
+may look like this:
+
+------------
+Here are lines that are either unchanged from the common
+ancestor, or cleanly resolved because only one side changed.
+<<<<<<< yours:sample.txt
+Conflict resolution is hard;
+let's go shopping.
+|||||||
+Conflict resolution is hard.
+=======
+Git makes conflict resolution easy.
+>>>>>>> theirs:sample.txt
+And here is another line that is cleanly resolved or unmodified.
+------------
+
+In addition to the "`<<<<<<<`", "`=======`", and "`>>>>>>>`" markers, it uses
+another "`|||||||`" marker that is followed by the original text.  You can
+tell that the original just stated a fact, and your side simply gave in to
+that statement and gave up, while the other side tried to have a more
+positive attitude.  You can sometimes come up with a better resolution by
+viewing the original.
+
+
+HOW TO RESOLVE CONFLICTS
+------------------------
+
 After seeing a conflict, you can do two things:
 
  * Decide not to merge.  The only clean-up you need are to reset