Merge branch 'js/merge'

* js/merge:
  merge-recursive: add/add really is modify/modify with an empty base
  Get rid of the dependency on RCS' merge program
  merge-file: support -p and -q; fix compile warnings
  Add builtin merge-file, a minimal replacement for RCS merge
  xdl_merge(): fix and simplify conflict handling
  xdl_merge(): fix thinko
  xdl_merge(): fix an off-by-one bug
  merge-recursive: use xdl_merge().
  xmerge: make return value from xdl_merge() more usable.
  xdiff: add xdl_merge()

19 files changed, 715 insertions, 179 deletions

diff --git a/.gitignore b/.gitignore
index 7f2cd5508..d706dd92c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -60,6 +60,7 @@ git-mailsplit
 git-merge
 git-merge-base
 git-merge-index
+git-merge-file
 git-merge-tree
 git-merge-octopus
 git-merge-one-file
diff --git a/Documentation/git-merge-index.txt b/Documentation/git-merge-index.txt
index 6cd060108..0cf505ea8 100644
--- a/Documentation/git-merge-index.txt
+++ b/Documentation/git-merge-index.txt
@@ -40,8 +40,8 @@ If "git-merge-index" is called with multiple <file>s (or -a) then it
 processes them in turn only stopping if merge returns a non-zero exit
 code.
 
-Typically this is run with the a script calling the merge command from
-the RCS package.
+Typically this is run with the a script calling git's imitation of
+the merge command from the RCS package.
 
 A sample script called "git-merge-one-file" is included in the
 distribution.
diff --git a/INSTALL b/INSTALL
index 8f69039fb..b5dd9f0ab 100644
--- a/INSTALL
+++ b/INSTALL
@@ -82,15 +82,6 @@ Issues of note:
 	  do that even if it wasn't for git.  There's no point in living
 	  in the dark ages any more. 
 
-	- "merge", the standard UNIX three-way merge program.  It usually
-	  comes with the "rcs" package on most Linux distributions, so if
-	  you have a developer install you probably have it already, but a
-	  "graphical user desktop" install might have left it out.
-
-	  You'll only need the merge program if you do development using
-	  git, and if you only use git to track other peoples work you'll
-	  never notice the lack of it. 
-
         - "wish", the Tcl/Tk windowing shell is used in gitk to show the
           history graphically
 
diff --git a/Makefile b/Makefile
index 906e98492..2d17fa702 100644
--- a/Makefile
+++ b/Makefile
@@ -279,6 +279,7 @@ BUILTIN_OBJS = \
 	builtin-ls-tree.o \
 	builtin-mailinfo.o \
 	builtin-mailsplit.o \
+	builtin-merge-file.o \
 	builtin-mv.o \
 	builtin-name-rev.o \
 	builtin-pack-objects.o \
@@ -737,7 +738,8 @@ $(DIFF_OBJS): diffcore.h
 $(LIB_FILE): $(LIB_OBJS)
 	rm -f $@ && $(AR) rcs $@ $(LIB_OBJS)
 
-XDIFF_OBJS=xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o
+XDIFF_OBJS=xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
+	xdiff/xmerge.o
 $(XDIFF_OBJS): xdiff/xinclude.h xdiff/xmacros.h xdiff/xdiff.h xdiff/xtypes.h \
 	xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h
 
diff --git a/builtin-merge-file.c b/builtin-merge-file.c
new file mode 100644
index 000000000..6c4c3a351
--- /dev/null
+++ b/builtin-merge-file.c
@@ -0,0 +1,79 @@
+#include "cache.h"
+#include "xdiff/xdiff.h"
+
+static const char merge_file_usage[] =
+"git merge-file [-p | --stdout] [-q | --quiet] [-L name1 [-L orig [-L name2]]] file1 orig_file file2";
+
+static int read_file(mmfile_t *ptr, const char *filename)
+{
+	struct stat st;
+	FILE *f;
+
+	if (stat(filename, &st))
+		return error("Could not stat %s", filename);
+	if ((f = fopen(filename, "rb")) == NULL)
+		return error("Could not open %s", filename);
+	ptr->ptr = xmalloc(st.st_size);
+	if (fread(ptr->ptr, st.st_size, 1, f) != 1)
+		return error("Could not read %s", filename);
+	fclose(f);
+	ptr->size = st.st_size;
+	return 0;
+}
+
+int cmd_merge_file(int argc, char **argv, char **envp)
+{
+	char *names[3];
+	mmfile_t mmfs[3];
+	mmbuffer_t result = {NULL, 0};
+	xpparam_t xpp = {XDF_NEED_MINIMAL};
+	int ret = 0, i = 0, to_stdout = 0;
+
+	while (argc > 4) {
+		if (!strcmp(argv[1], "-L") && i < 3) {
+			names[i++] = argv[2];
+			argc--;
+			argv++;
+		} else if (!strcmp(argv[1], "-p") ||
+				!strcmp(argv[1], "--stdout"))
+			to_stdout = 1;
+		else if (!strcmp(argv[1], "-q") ||
+				!strcmp(argv[1], "--quiet"))
+			freopen("/dev/null", "w", stderr);
+		else
+			usage(merge_file_usage);
+		argc--;
+		argv++;
+	}
+
+	if (argc != 4)
+		usage(merge_file_usage);
+
+	for (; i < 3; i++)
+		names[i] = argv[i + 1];
+
+	for (i = 0; i < 3; i++)
+		if (read_file(mmfs + i, argv[i + 1]))
+			return -1;
+
+	ret = xdl_merge(mmfs + 1, mmfs + 0, names[0], mmfs + 2, names[2],
+			&xpp, XDL_MERGE_ZEALOUS, &result);
+
+	for (i = 0; i < 3; i++)
+		free(mmfs[i].ptr);
+
+	if (ret >= 0) {
+		char *filename = argv[1];
+		FILE *f = to_stdout ? stdout : fopen(filename, "wb");
+
+		if (!f)
+			ret = error("Could not open %s for writing", filename);
+		else if (fwrite(result.ptr, result.size, 1, f) != 1)
+			ret = error("Could not write to %s", filename);
+		else if (fclose(f))
+			ret = error("Could not close %s", filename);
+		free(result.ptr);
+	}
+
+	return ret;
+}
diff --git a/builtin.h b/builtin.h
index b5116f30e..08519e7c8 100644
--- a/builtin.h
+++ b/builtin.h
@@ -42,6 +42,7 @@ extern int cmd_ls_files(int argc, const char **argv, const char *prefix);
 extern int cmd_ls_tree(int argc, const char **argv, const char *prefix);
 extern int cmd_mailinfo(int argc, const char **argv, const char *prefix);
 extern int cmd_mailsplit(int argc, const char **argv, const char *prefix);
+extern int cmd_merge_file(int argc, const char **argv, const char *prefix);
 extern int cmd_mv(int argc, const char **argv, const char *prefix);
 extern int cmd_name_rev(int argc, const char **argv, const char *prefix);
 extern int cmd_pack_objects(int argc, const char **argv, const char *prefix);
diff --git a/git-cvsserver.perl b/git-cvsserver.perl
index 197014d9e..2a8447e25 100755
--- a/git-cvsserver.perl
+++ b/git-cvsserver.perl
@@ -946,7 +946,7 @@ sub req_update
 
             $log->debug("Temporary directory for merge is $dir");
 
-            my $return = system("merge", $file_local, $file_old, $file_new);
+            my $return = system("git merge-file", $file_local, $file_old, $file_new);
             $return >>= 8;
 
             if ( $return == 0 )
diff --git a/git-rerere.perl b/git-rerere.perl
index d3664ff49..2e8dbbd4e 100755
--- a/git-rerere.perl
+++ b/git-rerere.perl
@@ -154,7 +154,7 @@ sub find_conflict {
 sub merge {
 	my ($name, $path) = @_;
 	record_preimage($path, "$rr_dir/$name/thisimage");
-	unless (system('merge', map { "$rr_dir/$name/${_}image" }
+	unless (system('git merge-file', map { "$rr_dir/$name/${_}image" }
 		       qw(this pre post))) {
 		my $in;
 		open $in, "<$rr_dir/$name/thisimage" or
diff --git a/git.c b/git.c
index 357330e02..016ee8adb 100644
--- a/git.c
+++ b/git.c
@@ -247,6 +247,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		{ "ls-tree", cmd_ls_tree, RUN_SETUP },
 		{ "mailinfo", cmd_mailinfo },
 		{ "mailsplit", cmd_mailsplit },
+		{ "merge-file", cmd_merge_file },
 		{ "mv", cmd_mv, RUN_SETUP },
 		{ "name-rev", cmd_name_rev, RUN_SETUP },
 		{ "pack-objects", cmd_pack_objects, RUN_SETUP },
diff --git a/git.spec.in b/git.spec.in
index f2374b733..fb95e3759 100644
--- a/git.spec.in
+++ b/git.spec.in
@@ -24,7 +24,7 @@ This is a dummy package which brings in all subpackages.
 %package core
 Summary:	Core git tools
 Group:		Development/Tools
-Requires:	zlib >= 1.2, rsync, rcs, curl, less, openssh-clients, expat
+Requires:	zlib >= 1.2, rsync, curl, less, openssh-clients, expat
 %description core
 This is a stupid (but extremely fast) directory content manager.  It
 doesn't do a whole lot, but what it _does_ do is track directory
diff --git a/merge-file.c b/merge-file.c
index fc9b14899..69dc1ebbf 100644
--- a/merge-file.c
+++ b/merge-file.c
@@ -3,52 +3,6 @@
 #include "xdiff-interface.h"
 #include "blob.h"
 
-static void rm_temp_file(const char *filename)
-{
-	unlink(filename);
-	free((void *)filename);
-}
-
-static const char *write_temp_file(mmfile_t *f)
-{
-	int fd;
-	const char *tmp = getenv("TMPDIR");
-	char *filename;
-
-	if (!tmp)
-		tmp = "/tmp";
-	filename = mkpath("%s/%s", tmp, "git-tmp-XXXXXX");
-	fd = mkstemp(filename);
-	if (fd < 0)
-		return NULL;
-	filename = xstrdup(filename);
-	if (f->size != xwrite(fd, f->ptr, f->size)) {
-		rm_temp_file(filename);
-		return NULL;
-	}
-	close(fd);
-	return filename;
-}
-
-static void *read_temp_file(const char *filename, unsigned long *size)
-{
-	struct stat st;
-	char *buf = NULL;
-	int fd = open(filename, O_RDONLY);
-	if (fd < 0)
-		return NULL;
-	if (!fstat(fd, &st)) {
-		*size = st.st_size;
-		buf = xmalloc(st.st_size);
-		if (st.st_size != xread(fd, buf, st.st_size)) {
-			free(buf);
-			buf = NULL;
-		}
-	}
-	close(fd);
-	return buf;
-}
-
 static int fill_mmfile_blob(mmfile_t *f, struct blob *obj)
 {
 	void *buf;
@@ -72,22 +26,19 @@ static void free_mmfile(mmfile_t *f)
 
 static void *three_way_filemerge(mmfile_t *base, mmfile_t *our, mmfile_t *their, unsigned long *size)
 {
-	void *res;
-	const char *t1, *t2, *t3;
-
-	t1 = write_temp_file(base);
-	t2 = write_temp_file(our);
-	t3 = write_temp_file(their);
-	res = NULL;
-	if (t1 && t2 && t3) {
-		int code = run_command("merge", t2, t1, t3, NULL);
-		if (!code || code == -1)
-			res = read_temp_file(t2, size);
-	}
-	rm_temp_file(t1);
-	rm_temp_file(t2);
-	rm_temp_file(t3);
-	return res;
+	mmbuffer_t res;
+	xpparam_t xpp;
+	int merge_status;
+
+	memset(&xpp, 0, sizeof(xpp));
+	merge_status = xdl_merge(base, our, ".our", their, ".their",
+		&xpp, XDL_MERGE_ZEALOUS, &res);
+
+	if (merge_status < 0)
+		return NULL;
+
+	*size = res.size;
+	return res.ptr;
 }
 
 static int common_outf(void *priv_, mmbuffer_t *mb, int nbuf)
diff --git a/merge-recursive.c b/merge-recursive.c
index 866a4e480..6dd6e2e5a 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -21,6 +21,7 @@
 #include "tag.h"
 #include "unpack-trees.h"
 #include "path-list.h"
+#include "xdiff-interface.h"
 
 /*
  * A virtual commit has
@@ -604,24 +605,21 @@ struct merge_file_info
 		 merge:1;
 };
 
-static char *git_unpack_file(const unsigned char *sha1, char *path)
+static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
 {
-	void *buf;
-	char type[20];
 	unsigned long size;
-	int fd;
+	char type[20];
 
-	buf = read_sha1_file(sha1, type, &size);
-	if (!buf || strcmp(type, blob_type))
-		die("unable to read blob object %s", sha1_to_hex(sha1));
+	if (!hashcmp(sha1, null_sha1)) {
+		mm->ptr = xstrdup("");
+		mm->size = 0;
+		return;
+	}
 
-	strcpy(path, ".merge_file_XXXXXX");
-	fd = mkstemp(path);
-	if (fd < 0)
-		die("unable to create temp-file");
-	flush_buffer(fd, buf, size);
-	close(fd);
-	return path;
+	mm->ptr = read_sha1_file(sha1, type, &size);
+	if (!mm->ptr || strcmp(type, blob_type))
+		die("unable to read blob object %s", sha1_to_hex(sha1));
+	mm->size = size;
 }
 
 static struct merge_file_info merge_file(struct diff_filespec *o,
@@ -652,49 +650,41 @@ static struct merge_file_info merge_file(struct diff_filespec *o,
 		else if (sha_eq(b->sha1, o->sha1))
 			hashcpy(result.sha, a->sha1);
 		else if (S_ISREG(a->mode)) {
-			int code = 1, fd;
-			struct stat st;
-			char orig[PATH_MAX];
-			char src1[PATH_MAX];
-			char src2[PATH_MAX];
-			const char *argv[] = {
-				"merge", "-L", NULL, "-L", NULL, "-L", NULL,
-				NULL, NULL, NULL,
-				NULL
-			};
-			char *la, *lb, *lo;
-
-			git_unpack_file(o->sha1, orig);
-			git_unpack_file(a->sha1, src1);
-			git_unpack_file(b->sha1, src2);
-
-			argv[2] = la = xstrdup(mkpath("%s/%s", branch1, a->path));
-			argv[6] = lb = xstrdup(mkpath("%s/%s", branch2, b->path));
-			argv[4] = lo = xstrdup(mkpath("orig/%s", o->path));
-			argv[7] = src1;
-			argv[8] = orig;
-			argv[9] = src2,
-
-			code = run_command_v(10, argv);
-
-			free(la);
-			free(lb);
-			free(lo);
-			if (code && code < -256) {
-				die("Failed to execute 'merge'. merge(1) is used as the "
-				    "file-level merge tool. Is 'merge' in your path?");
-			}
-			fd = open(src1, O_RDONLY);
-			if (fd < 0 || fstat(fd, &st) < 0 ||
-					index_fd(result.sha, fd, &st, 1,
-						"blob"))
-				die("Unable to add %s to database", src1);
-
-			unlink(orig);
-			unlink(src1);
-			unlink(src2);
-
-			result.clean = WEXITSTATUS(code) == 0;
+			mmfile_t orig, src1, src2;
+			mmbuffer_t result_buf;
+			xpparam_t xpp;
+			char *name1, *name2;
+			int merge_status;
+
+			name1 = xstrdup(mkpath("%s/%s", branch1, a->path));
+			name2 = xstrdup(mkpath("%s/%s", branch2, b->path));
+
+			fill_mm(o->sha1, &orig);
+			fill_mm(a->sha1, &src1);
+			fill_mm(b->sha1, &src2);
+
+			memset(&xpp, 0, sizeof(xpp));
+			merge_status = xdl_merge(&orig,
+						 &src1, name1,
+						 &src2, name2,
+						 &xpp, XDL_MERGE_ZEALOUS,
+						 &result_buf);
+			free(name1);
+			free(name2);
+			free(orig.ptr);
+			free(src1.ptr);
+			free(src2.ptr);
+
+			if ((merge_status < 0) || !result_buf.ptr)
+				die("Failed to execute internal merge");
+
+			if (write_sha1_file(result_buf.ptr, result_buf.size,
+					    blob_type, result.sha))
+				die("Unable to add %s to database",
+				    a->path);
+
+			free(result_buf.ptr);
+			result.clean = (merge_status == 0);
 		} else {
 			if (!(S_ISLNK(a->mode) || S_ISLNK(b->mode)))
 				die("cannot merge modes?");
@@ -1061,38 +1051,17 @@ static int process_entry(const char *path, struct stage_data *entry,
 			output("Adding %s", path);
 			update_file(1, sha, mode, path);
 		}
-	} else if (!o_sha && a_sha && b_sha) {
-		/* Case C: Added in both (check for same permissions). */
-		if (sha_eq(a_sha, b_sha)) {
-			if (a_mode != b_mode) {
-				clean_merge = 0;
-				output("CONFLICT: File %s added identically in both branches, "
-				       "but permissions conflict %06o->%06o",
-				       path, a_mode, b_mode);
-				output("CONFLICT: adding with permission: %06o", a_mode);
-				update_file(0, a_sha, a_mode, path);
-			} else {
-				/* This case is handled by git-read-tree */
-				assert(0 && "This case must be handled by git-read-tree");
-			}
-		} else {
-			const char *new_path1, *new_path2;
-			clean_merge = 0;
-			new_path1 = unique_path(path, branch1);
-			new_path2 = unique_path(path, branch2);
-			output("CONFLICT (add/add): File %s added non-identically "
-			       "in both branches. Adding as %s and %s instead.",
-			       path, new_path1, new_path2);
-			remove_file(0, path, 0);
-			update_file(0, a_sha, a_mode, new_path1);
-			update_file(0, b_sha, b_mode, new_path2);
-		}
-
-	} else if (o_sha && a_sha && b_sha) {
+	} else if (a_sha && b_sha) {
+		/* Case C: Added in both (check for same permissions) and */
 		/* case D: Modified in both, but differently. */
+		const char *reason = "content";
 		struct merge_file_info mfi;
 		struct diff_filespec o, a, b;
 
+		if (!o_sha) {
+			reason = "add/add";
+			o_sha = (unsigned char *)null_sha1;
+		}
 		output("Auto-merging %s", path);
 		o.path = a.path = b.path = (char *)path;
 		hashcpy(o.sha1, o_sha);
@@ -1109,7 +1078,8 @@ static int process_entry(const char *path, struct stage_data *entry,
 			update_file(1, mfi.sha, mfi.mode, path);
 		else {
 			clean_merge = 0;
-			output("CONFLICT (content): Merge conflict in %s", path);
+			output("CONFLICT (%s): Merge conflict in %s",
+					reason, path);
 
 			if (index_only)
 				update_file(0, mfi.sha, mfi.mode, path);
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 81f3bedc9..3260d1d7a 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -19,11 +19,7 @@ modification *should* take notice and update the test vectors here.
 '
 
 ################################################################
-# It appears that people are getting bitten by not installing
-# 'merge' (usually part of RCS package in binary distributions).
-# Check this and error out before running any tests.  Also catch
-# the bogosity of trying to run tests without building while we
-# are at it.
+# It appears that people try to run tests without building...
 
 ../git >/dev/null
 if test $? != 1
@@ -32,14 +28,6 @@ then
 	exit 1
 fi
 
-merge >/dev/null 2>/dev/null
-if test $? = 127
-then
-	echo >&2 'You do not seem to have "merge" installed.
-Please check INSTALL document.'
-	exit 1
-fi
-
 . ./test-lib.sh
 
 ################################################################
diff --git a/t/t6023-merge-file.sh b/t/t6023-merge-file.sh
new file mode 100644
index 000000000..5d9b6f34b
--- /dev/null
+++ b/t/t6023-merge-file.sh
@@ -0,0 +1,116 @@
+#!/bin/sh
+
+test_description='RCS merge replacement: merge-file'
+. ./test-lib.sh
+
+cat > orig.txt << EOF
+Dominus regit me,
+et nihil mihi deerit.
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+EOF
+
+cat > new1.txt << EOF
+Dominus regit me,
+et nihil mihi deerit.
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+Nam et si ambulavero in medio umbrae mortis,
+non timebo mala, quoniam tu mecum es:
+virga tua et baculus tuus ipsa me consolata sunt.
+EOF
+
+cat > new2.txt << EOF
+Dominus regit me, et nihil mihi deerit.
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+EOF
+
+cat > new3.txt << EOF
+DOMINUS regit me,
+et nihil mihi deerit.
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+EOF
+
+cat > new4.txt << EOF
+Dominus regit me, et nihil mihi deerit.
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+EOF
+echo -n "propter nomen suum." >> new4.txt
+
+cp new1.txt test.txt
+test_expect_success "merge without conflict" \
+	"git-merge-file test.txt orig.txt new2.txt"
+
+cp new1.txt test2.txt
+test_expect_success "merge without conflict (missing LF at EOF)" \
+	"git-merge-file test2.txt orig.txt new2.txt"
+
+test_expect_success "merge result added missing LF" \
+	"diff -u test.txt test2.txt"
+
+cp test.txt backup.txt
+test_expect_failure "merge with conflicts" \
+	"git-merge-file test.txt orig.txt new3.txt"
+
+cat > expect.txt << EOF
+<<<<<<< test.txt
+Dominus regit me, et nihil mihi deerit.
+=======
+DOMINUS regit me,
+et nihil mihi deerit.
+>>>>>>> new3.txt
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+Nam et si ambulavero in medio umbrae mortis,
+non timebo mala, quoniam tu mecum es:
+virga tua et baculus tuus ipsa me consolata sunt.
+EOF
+
+test_expect_success "expected conflict markers" "diff -u test.txt expect.txt"
+
+cp backup.txt test.txt
+test_expect_failure "merge with conflicts, using -L" \
+	"git-merge-file -L 1 -L 2 test.txt orig.txt new3.txt"
+
+cat > expect.txt << EOF
+<<<<<<< 1
+Dominus regit me, et nihil mihi deerit.
+=======
+DOMINUS regit me,
+et nihil mihi deerit.
+>>>>>>> new3.txt
+In loco pascuae ibi me collocavit,
+super aquam refectionis educavit me;
+animam meam convertit,
+deduxit me super semitas jusitiae,
+propter nomen suum.
+Nam et si ambulavero in medio umbrae mortis,
+non timebo mala, quoniam tu mecum es:
+virga tua et baculus tuus ipsa me consolata sunt.
+EOF
+
+test_expect_success "expected conflict markers, with -L" \
+	"diff -u test.txt expect.txt"
+
+test_done
+
diff --git a/t/t6024-recursive-merge.sh b/t/t6024-recursive-merge.sh
index 9416c271e..964010e76 100755..100644
--- a/t/t6024-recursive-merge.sh
+++ b/t/t6024-recursive-merge.sh
@@ -58,9 +58,19 @@ GIT_AUTHOR_DATE="2006-12-12 23:00:08" git commit -m F
 
 test_expect_failure "combined merge conflicts" "git merge -m final G"
 
+cat > expect << EOF
+<<<<<<< HEAD/a1
+F
+=======
+G
+>>>>>>> 26f86b677eb03d4d956dbe108b29cb77061c1e73/a1
+EOF
+
+test_expect_success "result contains a conflict" "diff -u expect a1"
+
 git ls-files --stage > out
 cat > expect << EOF
-100644 f70f10e4db19068f79bc43844b49f3eece45c4e8 1	a1
+100644 f16f906ab60483c100d1241dfc39868de9ec9fcb 1	a1
 100644 cf84443e49e1b366fac938711ddf4be2d4d1d9e9 2	a1
 100644 fd7923529855d0b274795ae3349c5e0438333979 3	a1
 EOF
diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
index c9f817818..fa409d523 100644
--- a/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@ -49,6 +49,9 @@ extern "C" {
 #define XDL_BDOP_CPY 2
 #define XDL_BDOP_INSB 3
 
+#define XDL_MERGE_MINIMAL 0
+#define XDL_MERGE_EAGER 1
+#define XDL_MERGE_ZEALOUS 2
 
 typedef struct s_mmfile {
 	char *ptr;
@@ -90,6 +93,10 @@ long xdl_mmfile_size(mmfile_t *mmf);
 int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	     xdemitconf_t const *xecfg, xdemitcb_t *ecb);
 
+int xdl_merge(mmfile_t *orig, mmfile_t *mf1, const char *name1,
+		mmfile_t *mf2, const char *name2,
+		xpparam_t const *xpp, int level, mmbuffer_t *result);
+
 #ifdef __cplusplus
 }
 #endif /* #ifdef __cplusplus */
diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index d76e76a0e..9aeebc473 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -45,7 +45,6 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
 		      xdalgoenv_t *xenv);
 static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2);
-static int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags);
 
 
 
@@ -397,7 +396,7 @@ static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1,
 }
 
 
-static int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 	long ix, ixo, ixs, ixref, grpsiz, nrec = xdf->nrec;
 	char *rchg = xdf->rchg, *rchgo = xdfo->rchg;
 	xrecord_t **recs = xdf->recs;
diff --git a/xdiff/xdiffi.h b/xdiff/xdiffi.h
index d3b72716b..472aeaecf 100644
--- a/xdiff/xdiffi.h
+++ b/xdiff/xdiffi.h
@@ -50,6 +50,7 @@ int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
 		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv);
 int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 		xdfenv_t *xe);
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags);
 int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr);
 void xdl_free_script(xdchange_t *xscr);
 int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
diff --git a/xdiff/xmerge.c b/xdiff/xmerge.c
new file mode 100644
index 000000000..352207e51
--- /dev/null
+++ b/xdiff/xmerge.c
@@ -0,0 +1,419 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003-2006 Davide Libenzi, Johannes E. Schindelin
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+typedef struct s_xdmerge {
+	struct s_xdmerge *next;
+	/*
+	 * 0 = conflict,
+	 * 1 = no conflict, take first,
+	 * 2 = no conflict, take second.
+	 */
+	int mode;
+	long i1, i2;
+	long chg1, chg2;
+} xdmerge_t;
+
+static int xdl_append_merge(xdmerge_t **merge, int mode,
+		long i1, long chg1, long i2, long chg2)
+{
+	xdmerge_t *m = *merge;
+	if (m && (i1 <= m->i1 + m->chg1 || i2 <= m->i2 + m->chg2)) {
+		if (mode != m->mode)
+			m->mode = 0;
+		m->chg1 = i1 + chg1 - m->i1;
+		m->chg2 = i2 + chg2 - m->i2;
+	} else {
+		m = xdl_malloc(sizeof(xdmerge_t));
+		if (!m)
+			return -1;
+		m->next = NULL;
+		m->mode = mode;
+		m->i1 = i1;
+		m->chg1 = chg1;
+		m->i2 = i2;
+		m->chg2 = chg2;
+		if (*merge)
+			(*merge)->next = m;
+		*merge = m;
+	}
+	return 0;
+}
+
+static int xdl_cleanup_merge(xdmerge_t *c)
+{
+	int count = 0;
+	xdmerge_t *next_c;
+
+	/* were there conflicts? */
+	for (; c; c = next_c) {
+		if (c->mode == 0)
+			count++;
+		next_c = c->next;
+		free(c);
+	}
+	return count;
+}
+
+static int xdl_merge_cmp_lines(xdfenv_t *xe1, int i1, xdfenv_t *xe2, int i2,
+		int line_count, long flags)
+{
+	int i;
+	xrecord_t **rec1 = xe1->xdf2.recs + i1;
+	xrecord_t **rec2 = xe2->xdf2.recs + i2;
+
+	for (i = 0; i < line_count; i++) {
+		int result = xdl_recmatch(rec1[i]->ptr, rec1[i]->size,
+			rec2[i]->ptr, rec2[i]->size, flags);
+		if (!result)
+			return -1;
+	}
+	return 0;
+}
+
+static int xdl_recs_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
+{
+	xrecord_t **recs = xe->xdf2.recs + i;
+	int size = 0;
+
+	if (count < 1)
+		return 0;
+
+	for (i = 0; i < count; size += recs[i++]->size)
+		if (dest)
+			memcpy(dest + size, recs[i]->ptr, recs[i]->size);
+	if (add_nl) {
+		i = recs[count - 1]->size;
+		if (i == 0 || recs[count - 1]->ptr[i - 1] != '\n') {
+			if (dest)
+				dest[size] = '\n';
+			size++;
+		}
+	}
+	return size;
+}
+
+static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
+		xdfenv_t *xe2, const char *name2, xdmerge_t *m, char *dest)
+{
+	const int marker_size = 7;
+	int marker1_size = (name1 ? strlen(name1) + 1 : 0);
+	int marker2_size = (name2 ? strlen(name2) + 1 : 0);
+	int conflict_marker_size = 3 * (marker_size + 1)
+		+ marker1_size + marker2_size;
+	int size, i1, j;
+
+	for (size = i1 = 0; m; m = m->next) {
+		if (m->mode == 0) {
+			size += xdl_recs_copy(xe1, i1, m->i1 - i1, 0,
+					dest ? dest + size : NULL);
+			if (dest) {
+				for (j = 0; j < marker_size; j++)
+					dest[size++] = '<';
+				if (marker1_size) {
+					dest[size] = ' ';
+					memcpy(dest + size + 1, name1,
+							marker1_size - 1);
+					size += marker1_size;
+				}
+				dest[size++] = '\n';
+			} else
+				size += conflict_marker_size;
+			size += xdl_recs_copy(xe1, m->i1, m->chg1, 1,
+					dest ? dest + size : NULL);
+			if (dest) {
+				for (j = 0; j < marker_size; j++)
+					dest[size++] = '=';
+				dest[size++] = '\n';
+			}
+			size += xdl_recs_copy(xe2, m->i2, m->chg2, 1,
+					dest ? dest + size : NULL);
+			if (dest) {
+				for (j = 0; j < marker_size; j++)
+					dest[size++] = '>';
+				if (marker2_size) {
+					dest[size] = ' ';
+					memcpy(dest + size + 1, name2,
+							marker2_size - 1);
+					size += marker2_size;
+				}
+				dest[size++] = '\n';
+			}
+		} else if (m->mode == 1)
+			size += xdl_recs_copy(xe1, i1, m->i1 + m->chg1 - i1, 0,
+					dest ? dest + size : NULL);
+		else if (m->mode == 2)
+			size += xdl_recs_copy(xe2, m->i2 - m->i1 + i1,
+					m->i1 + m->chg2 - i1, 0,
+					dest ? dest + size : NULL);
+		i1 = m->i1 + m->chg1;
+	}
+	size += xdl_recs_copy(xe1, i1, xe1->xdf2.nrec - i1, 0,
+			dest ? dest + size : NULL);
+	return size;
+}
+
+/*
+ * Sometimes, changes are not quite identical, but differ in only a few
+ * lines. Try hard to show only these few lines as conflicting.
+ */
+static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
+		xpparam_t const *xpp)
+{
+	for (; m; m = m->next) {
+		mmfile_t t1, t2;
+		xdfenv_t xe;
+		xdchange_t *xscr, *x;
+		int i1 = m->i1, i2 = m->i2;
+
+		/* let's handle just the conflicts */
+		if (m->mode)
+			continue;
+
+		/*
+		 * This probably does not work outside git, since
+		 * we have a very simple mmfile structure.
+		 */
+		t1.ptr = (char *)xe1->xdf2.recs[m->i1]->ptr;
+		t1.size = xe1->xdf2.recs[m->i1 + m->chg1 - 1]->ptr
+			+ xe1->xdf2.recs[m->i1 + m->chg1 - 1]->size - t1.ptr;
+		t2.ptr = (char *)xe2->xdf2.recs[m->i2]->ptr;
+		t2.size = xe2->xdf2.recs[m->i2 + m->chg2 - 1]->ptr
+			+ xe2->xdf2.recs[m->i2 + m->chg2 - 1]->size - t2.ptr;
+		if (xdl_do_diff(&t1, &t2, xpp, &xe) < 0)
+			return -1;
+		if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
+		    xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
+		    xdl_build_script(&xe, &xscr) < 0) {
+			xdl_free_env(&xe);
+			return -1;
+		}
+		if (!xscr) {
+			/* If this happens, it's a bug. */
+			xdl_free_env(&xe);
+			return -2;
+		}
+		x = xscr;
+		m->i1 = xscr->i1 + i1;
+		m->chg1 = xscr->chg1;
+		m->i2 = xscr->i2 + i2;
+		m->chg2 = xscr->chg2;
+		while (xscr->next) {
+			xdmerge_t *m2 = xdl_malloc(sizeof(xdmerge_t));
+			if (!m2) {
+				xdl_free_env(&xe);
+				xdl_free_script(x);
+				return -1;
+			}
+			xscr = xscr->next;
+			m2->next = m->next;
+			m->next = m2;
+			m = m2;
+			m->mode = 0;
+			m->i1 = xscr->i1 + i1;
+			m->chg1 = xscr->chg1;
+			m->i2 = xscr->i2 + i2;
+			m->chg2 = xscr->chg2;
+		}
+		xdl_free_env(&xe);
+		xdl_free_script(x);
+	}
+	return 0;
+}
+
+/*
+ * level == 0: mark all overlapping changes as conflict
+ * level == 1: mark overlapping changes as conflict only if not identical
+ * level == 2: analyze non-identical changes for minimal conflict set
+ *
+ * returns < 0 on error, == 0 for no conflicts, else number of conflicts
+ */
+static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1, const char *name1,
+		xdfenv_t *xe2, xdchange_t *xscr2, const char *name2,
+		int level, xpparam_t const *xpp, mmbuffer_t *result) {
+	xdmerge_t *changes, *c;
+	int i1, i2, chg1, chg2;
+
+	c = changes = NULL;
+
+	while (xscr1 && xscr2) {
+		if (!changes)
+			changes = c;
+		if (xscr1->i1 + xscr1->chg1 < xscr2->i1) {
+			i1 = xscr1->i2;
+			i2 = xscr2->i2 - xscr2->i1 + xscr1->i1;
+			chg1 = xscr1->chg2;
+			chg2 = xscr1->chg1;
+			if (xdl_append_merge(&c, 1, i1, chg1, i2, chg2)) {
+				xdl_cleanup_merge(changes);
+				return -1;
+			}
+			xscr1 = xscr1->next;
+			continue;
+		}
+		if (xscr2->i1 + xscr2->chg1 < xscr1->i1) {
+			i1 = xscr1->i2 - xscr1->i1 + xscr2->i1;
+			i2 = xscr2->i2;
+			chg1 = xscr2->chg1;
+			chg2 = xscr2->chg2;
+			if (xdl_append_merge(&c, 2, i1, chg1, i2, chg2)) {
+				xdl_cleanup_merge(changes);
+				return -1;
+			}
+			xscr2 = xscr2->next;
+			continue;
+		}
+		if (level < 1 || xscr1->i1 != xscr2->i1 ||
+				xscr1->chg1 != xscr2->chg1 ||
+				xscr1->chg2 != xscr2->chg2 ||
+				xdl_merge_cmp_lines(xe1, xscr1->i2,
+					xe2, xscr2->i2,
+					xscr1->chg2, xpp->flags)) {
+			/* conflict */
+			int off = xscr1->i1 - xscr2->i1;
+			int ffo = off + xscr1->chg1 - xscr2->chg1;
+
+			i1 = xscr1->i2;
+			i2 = xscr2->i2;
+			if (off > 0)
+				i1 -= off;
+			else
+				i2 += off;
+			chg1 = xscr1->i2 + xscr1->chg2 - i1;
+			chg2 = xscr2->i2 + xscr2->chg2 - i2;
+			if (ffo > 0)
+				chg2 += ffo;
+			else
+				chg1 -= ffo;
+			if (xdl_append_merge(&c, 0, i1, chg1, i2, chg2)) {
+				xdl_cleanup_merge(changes);
+				return -1;
+			}
+		}
+
+		i1 = xscr1->i1 + xscr1->chg1;
+		i2 = xscr2->i1 + xscr2->chg1;
+
+		if (i1 >= i2)
+			xscr2 = xscr2->next;
+		if (i2 >= i1)
+			xscr1 = xscr1->next;
+	}
+	while (xscr1) {
+		if (!changes)
+			changes = c;
+		i1 = xscr1->i2;
+		i2 = xscr1->i1 + xe2->xdf2.nrec - xe2->xdf1.nrec;
+		chg1 = xscr1->chg2;
+		chg2 = xscr1->chg1;
+		if (xdl_append_merge(&c, 1, i1, chg1, i2, chg2)) {
+			xdl_cleanup_merge(changes);
+			return -1;
+		}
+		xscr1 = xscr1->next;
+	}
+	while (xscr2) {
+		if (!changes)
+			changes = c;
+		i1 = xscr2->i1 + xe1->xdf2.nrec - xe1->xdf1.nrec;
+		i2 = xscr2->i2;
+		chg1 = xscr2->chg1;
+		chg2 = xscr2->chg2;
+		if (xdl_append_merge(&c, 2, i1, chg1, i2, chg2)) {
+			xdl_cleanup_merge(changes);
+			return -1;
+		}
+		xscr2 = xscr2->next;
+	}
+	if (!changes)
+		changes = c;
+	/* refine conflicts */
+	if (level > 1 && xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0) {
+		xdl_cleanup_merge(changes);
+		return -1;
+	}
+	/* output */
+	if (result) {
+		int size = xdl_fill_merge_buffer(xe1, name1, xe2, name2,
+			changes, NULL);
+		result->ptr = xdl_malloc(size);
+		if (!result->ptr) {
+			xdl_cleanup_merge(changes);
+			return -1;
+		}
+		result->size = size;
+		xdl_fill_merge_buffer(xe1, name1, xe2, name2, changes,
+				result->ptr);
+	}
+	return xdl_cleanup_merge(changes);
+}
+
+int xdl_merge(mmfile_t *orig, mmfile_t *mf1, const char *name1,
+		mmfile_t *mf2, const char *name2,
+		xpparam_t const *xpp, int level, mmbuffer_t *result) {
+	xdchange_t *xscr1, *xscr2;
+	xdfenv_t xe1, xe2;
+	int status;
+
+	result->ptr = NULL;
+	result->size = 0;
+
+	if (xdl_do_diff(orig, mf1, xpp, &xe1) < 0 ||
+			xdl_do_diff(orig, mf2, xpp, &xe2) < 0) {
+		return -1;
+	}
+	if (xdl_change_compact(&xe1.xdf1, &xe1.xdf2, xpp->flags) < 0 ||
+	    xdl_change_compact(&xe1.xdf2, &xe1.xdf1, xpp->flags) < 0 ||
+	    xdl_build_script(&xe1, &xscr1) < 0) {
+		xdl_free_env(&xe1);
+		return -1;
+	}
+	if (xdl_change_compact(&xe2.xdf1, &xe2.xdf2, xpp->flags) < 0 ||
+	    xdl_change_compact(&xe2.xdf2, &xe2.xdf1, xpp->flags) < 0 ||
+	    xdl_build_script(&xe2, &xscr2) < 0) {
+		xdl_free_env(&xe2);
+		return -1;
+	}
+	status = 0;
+	if (xscr1 || xscr2) {
+		if (!xscr1) {
+			result->ptr = xdl_malloc(mf2->size);
+			memcpy(result->ptr, mf2->ptr, mf2->size);
+			result->size = mf2->size;
+		} else if (!xscr2) {
+			result->ptr = xdl_malloc(mf1->size);
+			memcpy(result->ptr, mf1->ptr, mf1->size);
+			result->size = mf1->size;
+		} else {
+			status = xdl_do_merge(&xe1, xscr1, name1,
+					      &xe2, xscr2, name2,
+					      level, xpp, result);
+		}
+		xdl_free_script(xscr1);
+		xdl_free_script(xscr2);
+	}
+	xdl_free_env(&xe1);
+	xdl_free_env(&xe2);
+
+	return status;
+}