Merge branch 'lt/reset-merge'

* lt/reset-merge:
  Document "git-reset --merge"
  Add 'merge' mode to 'git reset'

Documentation/git-reset.txt

@@ -8,7 +8,7 @@ git-reset - Reset current HEAD to the specified state
 SYNOPSIS
 --------
 [verse]
-'git reset' [--mixed | --soft | --hard] [-q] [<commit>]
+'git reset' [--mixed | --soft | --hard | --merge] [-q] [<commit>]
 'git reset' [-q] [<commit>] [--] <paths>...
 
 DESCRIPTION
@@ -45,6 +45,11 @@ OPTIONS
 	switched to. Any changes to tracked files in the working tree
 	since <commit> are lost.
 
+--merge::
+	Resets the index to match the tree recorded by the named commit,
+	and updates the files that are different between the named commit
+	and the current commit in the working tree.
+
 -q::
 	Be quiet, only report errors.
 
@@ -152,6 +157,28 @@ tip of the current branch in ORIG_HEAD, so resetting hard to it
 brings your index file and the working tree back to that state,
 and resets the tip of the branch to that commit.
 
+Undo a merge or pull inside a dirty work tree::
++
+------------
+$ git pull                         <1>
+Auto-merging nitfol
+Merge made by recursive.
+ nitfol                |   20 +++++----
+ ...
+$ git reset --merge ORIG_HEAD      <2>
+------------
++
+<1> Even if you may have local modifications in your
+working tree, you can safely say "git pull" when you know
+that the change in the other branch does not overlap with
+them.
+<2> After inspecting the result of the merge, you may find
+that the change in the other branch is unsatisfactory.  Running
+"git reset --hard ORIG_HEAD" will let you go back to where you
+were, but it will discard your local changes, which you do not
+want.  "git reset --merge" keeps your local changes.
+
+
 Interrupted workflow::
 +
 Suppose you are interrupted by an urgent fix request while you

builtin-reset.c

@@ -20,11 +20,14 @@
 #include "parse-options.h"
 
 static const char * const git_reset_usage[] = {
-	"git reset [--mixed | --soft | --hard] [-q] [<commit>]",
+	"git reset [--mixed | --soft | --hard | --merge] [-q] [<commit>]",
 	"git reset [--mixed] <commit> [--] <paths>...",
 	NULL
 };
 
+enum reset_type { MIXED, SOFT, HARD, MERGE, NONE };
+static const char *reset_type_names[] = { "mixed", "soft", "hard", "merge", NULL };
+
 static char *args_to_str(const char **argv)
 {
 	char *buf = NULL;
@@ -49,17 +52,25 @@ static inline int is_merge(void)
 	return !access(git_path("MERGE_HEAD"), F_OK);
 }
 
-static int reset_index_file(const unsigned char *sha1, int is_hard_reset, int quiet)
+static int reset_index_file(const unsigned char *sha1, int reset_type, int quiet)
 {
 	int i = 0;
 	const char *args[6];
 
 	args[i++] = "read-tree";
 	if (!quiet)
 		args[i++] = "-v";
-	args[i++] = "--reset";
-	if (is_hard_reset)
+	switch (reset_type) {
+	case MERGE:
 		args[i++] = "-u";
+		args[i++] = "-m";
+		break;
+	case HARD:
+		args[i++] = "-u";
+		/* fallthrough */
+	default:
+		args[i++] = "--reset";
+	}
 	args[i++] = sha1_to_hex(sha1);
 	args[i] = NULL;
 
@@ -169,9 +180,6 @@ static void prepend_reflog_action(const char *action, char *buf, size_t size)
 		warning("Reflog action message too long: %.*s...", 50, buf);
 }
 
-enum reset_type { MIXED, SOFT, HARD, NONE };
-static const char *reset_type_names[] = { "mixed", "soft", "hard", NULL };
-
 int cmd_reset(int argc, const char **argv, const char *prefix)
 {
 	int i = 0, reset_type = NONE, update_ref_status = 0, quiet = 0;
@@ -186,6 +194,8 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		OPT_SET_INT(0, "soft", &reset_type, "reset only HEAD", SOFT),
 		OPT_SET_INT(0, "hard", &reset_type,
 				"reset HEAD, index and working tree", HARD),
+		OPT_SET_INT(0, "merge", &reset_type,
+				"reset HEAD, index and working tree", MERGE),
 		OPT_BOOLEAN('q', NULL, &quiet,
 				"disable showing new HEAD in hard reset and progress message"),
 		OPT_END()
@@ -266,7 +276,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		if (is_merge() || read_cache() < 0 || unmerged_cache())
 			die("Cannot do a soft reset in the middle of a merge.");
 	}
-	else if (reset_index_file(sha1, (reset_type == HARD), quiet))
+	else if (reset_index_file(sha1, reset_type, quiet))
 		die("Could not reset index file to revision '%s'.", rev);
 
 	/* Any resets update HEAD to the head being switched to,