Merge branch 'jc/cherry-pick' (early part)

* 'jc/cherry-pick' (early part):
  expose a helper function peel_to_type().
  merge-recursive: split low-level merge functions out.

Conflicts:

	Makefile
	builtin-merge-recursive.c
	sha1_name.c

6 files changed, 449 insertions, 389 deletions

diff --git a/Makefile b/Makefile
index 7fbb815782..514738046f 100644
--- a/Makefile
+++ b/Makefile
@@ -308,7 +308,7 @@ LIB_H = \
 	run-command.h strbuf.h tag.h tree.h git-compat-util.h revision.h \
 	tree-walk.h log-tree.h dir.h path-list.h unpack-trees.h builtin.h \
 	utf8.h reflog-walk.h patch-ids.h attr.h decorate.h progress.h \
-	mailmap.h remote.h parse-options.h transport.h diffcore.h hash.h fsck.h \
+	mailmap.h remote.h parse-options.h transport.h diffcore.h hash.h ll-merge.h fsck.h \
 	pack-revindex.h
 
 DIFF_OBJS = \
@@ -333,7 +333,7 @@ LIB_OBJS = \
 	color.o wt-status.o archive-zip.o archive-tar.o shallow.o utf8.o \
 	convert.o attr.o decorate.o progress.o mailmap.o symlinks.o remote.o \
 	transport.o bundle.o walker.o parse-options.o ws.o archive.o branch.o \
-	alias.o fsck.o pack-revindex.o
+	ll-merge.o alias.o fsck.o pack-revindex.o
 
 BUILTIN_OBJS = \
 	builtin-add.o \
diff --git a/builtin-merge-recursive.c b/builtin-merge-recursive.c
index 6fe4102c0c..5a0a7b5297 100644
--- a/builtin-merge-recursive.c
+++ b/builtin-merge-recursive.c
@@ -11,11 +11,11 @@
 #include "tree-walk.h"
 #include "diff.h"
 #include "diffcore.h"
-#include "run-command.h"
 #include "tag.h"
 #include "unpack-trees.h"
 #include "path-list.h"
 #include "xdiff-interface.h"
+#include "ll-merge.h"
 #include "interpolate.h"
 #include "attr.h"
 #include "merge-recursive.h"
@@ -615,364 +615,16 @@ static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
 	mm->size = size;
 }
 
-/*
- * Customizable low-level merge drivers support.
- */
-
-struct ll_merge_driver;
-typedef int (*ll_merge_fn)(const struct ll_merge_driver *,
-			   const char *path,
-			   mmfile_t *orig,
-			   mmfile_t *src1, const char *name1,
-			   mmfile_t *src2, const char *name2,
-			   mmbuffer_t *result);
-
-struct ll_merge_driver {
-	const char *name;
-	const char *description;
-	ll_merge_fn fn;
-	const char *recursive;
-	struct ll_merge_driver *next;
-	char *cmdline;
-};
-
-/*
- * Built-in low-levels
- */
-static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
-			   const char *path_unused,
-			   mmfile_t *orig,
-			   mmfile_t *src1, const char *name1,
-			   mmfile_t *src2, const char *name2,
-			   mmbuffer_t *result)
-{
-	/*
-	 * The tentative merge result is "ours" for the final round,
-	 * or common ancestor for an internal merge.  Still return
-	 * "conflicted merge" status.
-	 */
-	mmfile_t *stolen = index_only ? orig : src1;
-
-	result->ptr = stolen->ptr;
-	result->size = stolen->size;
-	stolen->ptr = NULL;
-	return 1;
-}
-
-static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
-			const char *path_unused,
-			mmfile_t *orig,
-			mmfile_t *src1, const char *name1,
-			mmfile_t *src2, const char *name2,
-			mmbuffer_t *result)
-{
-	xpparam_t xpp;
-
-	if (buffer_is_binary(orig->ptr, orig->size) ||
-	    buffer_is_binary(src1->ptr, src1->size) ||
-	    buffer_is_binary(src2->ptr, src2->size)) {
-		warning("Cannot merge binary files: %s vs. %s\n",
-			name1, name2);
-		return ll_binary_merge(drv_unused, path_unused,
-				       orig, src1, name1,
-				       src2, name2,
-				       result);
-	}
-
-	memset(&xpp, 0, sizeof(xpp));
-	return xdl_merge(orig,
-			 src1, name1,
-			 src2, name2,
-			 &xpp, XDL_MERGE_ZEALOUS,
-			 result);
-}
-
-static int ll_union_merge(const struct ll_merge_driver *drv_unused,
-			  const char *path_unused,
-			  mmfile_t *orig,
-			  mmfile_t *src1, const char *name1,
-			  mmfile_t *src2, const char *name2,
-			  mmbuffer_t *result)
-{
-	char *src, *dst;
-	long size;
-	const int marker_size = 7;
-
-	int status = ll_xdl_merge(drv_unused, path_unused,
-				  orig, src1, NULL, src2, NULL, result);
-	if (status <= 0)
-		return status;
-	size = result->size;
-	src = dst = result->ptr;
-	while (size) {
-		char ch;
-		if ((marker_size < size) &&
-		    (*src == '<' || *src == '=' || *src == '>')) {
-			int i;
-			ch = *src;
-			for (i = 0; i < marker_size; i++)
-				if (src[i] != ch)
-					goto not_a_marker;
-			if (src[marker_size] != '\n')
-				goto not_a_marker;
-			src += marker_size + 1;
-			size -= marker_size + 1;
-			continue;
-		}
-	not_a_marker:
-		do {
-			ch = *src++;
-			*dst++ = ch;
-			size--;
-		} while (ch != '\n' && size);
-	}
-	result->size = dst - result->ptr;
-	return 0;
-}
-
-#define LL_BINARY_MERGE 0
-#define LL_TEXT_MERGE 1
-#define LL_UNION_MERGE 2
-static struct ll_merge_driver ll_merge_drv[] = {
-	{ "binary", "built-in binary merge", ll_binary_merge },
-	{ "text", "built-in 3-way text merge", ll_xdl_merge },
-	{ "union", "built-in union merge", ll_union_merge },
-};
-
-static void create_temp(mmfile_t *src, char *path)
-{
-	int fd;
-
-	strcpy(path, ".merge_file_XXXXXX");
-	fd = xmkstemp(path);
-	if (write_in_full(fd, src->ptr, src->size) != src->size)
-		die("unable to write temp-file");
-	close(fd);
-}
-
-/*
- * User defined low-level merge driver support.
- */
-static int ll_ext_merge(const struct ll_merge_driver *fn,
-			const char *path,
-			mmfile_t *orig,
-			mmfile_t *src1, const char *name1,
-			mmfile_t *src2, const char *name2,
-			mmbuffer_t *result)
-{
-	char temp[3][50];
-	char cmdbuf[2048];
-	struct interp table[] = {
-		{ "%O" },
-		{ "%A" },
-		{ "%B" },
-	};
-	struct child_process child;
-	const char *args[20];
-	int status, fd, i;
-	struct stat st;
-
-	if (fn->cmdline == NULL)
-		die("custom merge driver %s lacks command line.", fn->name);
-
-	result->ptr = NULL;
-	result->size = 0;
-	create_temp(orig, temp[0]);
-	create_temp(src1, temp[1]);
-	create_temp(src2, temp[2]);
-
-	interp_set_entry(table, 0, temp[0]);
-	interp_set_entry(table, 1, temp[1]);
-	interp_set_entry(table, 2, temp[2]);
-
-	output(1, "merging %s using %s", path,
-	       fn->description ? fn->description : fn->name);
-
-	interpolate(cmdbuf, sizeof(cmdbuf), fn->cmdline, table, 3);
-
-	memset(&child, 0, sizeof(child));
-	child.argv = args;
-	args[0] = "sh";
-	args[1] = "-c";
-	args[2] = cmdbuf;
-	args[3] = NULL;
-
-	status = run_command(&child);
-	if (status < -ERR_RUN_COMMAND_FORK)
-		; /* failure in run-command */
-	else
-		status = -status;
-	fd = open(temp[1], O_RDONLY);
-	if (fd < 0)
-		goto bad;
-	if (fstat(fd, &st))
-		goto close_bad;
-	result->size = st.st_size;
-	result->ptr = xmalloc(result->size + 1);
-	if (read_in_full(fd, result->ptr, result->size) != result->size) {
-		free(result->ptr);
-		result->ptr = NULL;
-		result->size = 0;
-	}
- close_bad:
-	close(fd);
- bad:
-	for (i = 0; i < 3; i++)
-		unlink(temp[i]);
-	return status;
-}
-
-/*
- * merge.default and merge.driver configuration items
- */
-static struct ll_merge_driver *ll_user_merge, **ll_user_merge_tail;
-static const char *default_ll_merge;
-
-static int read_merge_config(const char *var, const char *value)
-{
-	struct ll_merge_driver *fn;
-	const char *ep, *name;
-	int namelen;
-
-	if (!strcmp(var, "merge.default")) {
-		if (!value)
-			return config_error_nonbool(var);
-		default_ll_merge = strdup(value);
-		return 0;
-	}
-
-	/*
-	 * We are not interested in anything but "merge.<name>.variable";
-	 * especially, we do not want to look at variables such as
-	 * "merge.summary", "merge.tool", and "merge.verbosity".
-	 */
-	if (prefixcmp(var, "merge.") || (ep = strrchr(var, '.')) == var + 5)
-		return 0;
-
-	/*
-	 * Find existing one as we might be processing merge.<name>.var2
-	 * after seeing merge.<name>.var1.
-	 */
-	name = var + 6;
-	namelen = ep - name;
-	for (fn = ll_user_merge; fn; fn = fn->next)
-		if (!strncmp(fn->name, name, namelen) && !fn->name[namelen])
-			break;
-	if (!fn) {
-		fn = xcalloc(1, sizeof(struct ll_merge_driver));
-		fn->name = xmemdupz(name, namelen);
-		fn->fn = ll_ext_merge;
-		*ll_user_merge_tail = fn;
-		ll_user_merge_tail = &(fn->next);
-	}
-
-	ep++;
-
-	if (!strcmp("name", ep)) {
-		if (!value)
-			return config_error_nonbool(var);
-		fn->description = strdup(value);
-		return 0;
-	}
-
-	if (!strcmp("driver", ep)) {
-		if (!value)
-			return config_error_nonbool(var);
-		/*
-		 * merge.<name>.driver specifies the command line:
-		 *
-		 *	command-line
-		 *
-		 * The command-line will be interpolated with the following
-		 * tokens and is given to the shell:
-		 *
-		 *    %O - temporary file name for the merge base.
-		 *    %A - temporary file name for our version.
-		 *    %B - temporary file name for the other branches' version.
-		 *
-		 * The external merge driver should write the results in the
-		 * file named by %A, and signal that it has done with zero exit
-		 * status.
-		 */
-		fn->cmdline = strdup(value);
-		return 0;
-	}
-
-	if (!strcmp("recursive", ep)) {
-		if (!value)
-			return config_error_nonbool(var);
-		fn->recursive = strdup(value);
-		return 0;
-	}
-
-	return 0;
-}
-
-static void initialize_ll_merge(void)
-{
-	if (ll_user_merge_tail)
-		return;
-	ll_user_merge_tail = &ll_user_merge;
-	git_config(read_merge_config);
-}
-
-static const struct ll_merge_driver *find_ll_merge_driver(const char *merge_attr)
-{
-	struct ll_merge_driver *fn;
-	const char *name;
-	int i;
-
-	initialize_ll_merge();
-
-	if (ATTR_TRUE(merge_attr))
-		return &ll_merge_drv[LL_TEXT_MERGE];
-	else if (ATTR_FALSE(merge_attr))
-		return &ll_merge_drv[LL_BINARY_MERGE];
-	else if (ATTR_UNSET(merge_attr)) {
-		if (!default_ll_merge)
-			return &ll_merge_drv[LL_TEXT_MERGE];
-		else
-			name = default_ll_merge;
-	}
-	else
-		name = merge_attr;
-
-	for (fn = ll_user_merge; fn; fn = fn->next)
-		if (!strcmp(fn->name, name))
-			return fn;
-
-	for (i = 0; i < ARRAY_SIZE(ll_merge_drv); i++)
-		if (!strcmp(ll_merge_drv[i].name, name))
-			return &ll_merge_drv[i];
-
-	/* default to the 3-way */
-	return &ll_merge_drv[LL_TEXT_MERGE];
-}
-
-static const char *git_path_check_merge(const char *path)
-{
-	static struct git_attr_check attr_merge_check;
-
-	if (!attr_merge_check.attr)
-		attr_merge_check.attr = git_attr("merge", 5);
-
-	if (git_checkattr(path, 1, &attr_merge_check))
-		return NULL;
-	return attr_merge_check.value;
-}
-
-static int ll_merge(mmbuffer_t *result_buf,
-		    struct diff_filespec *o,
-		    struct diff_filespec *a,
-		    struct diff_filespec *b,
-		    const char *branch1,
-		    const char *branch2)
+static int merge_3way(mmbuffer_t *result_buf,
+		      struct diff_filespec *o,
+		      struct diff_filespec *a,
+		      struct diff_filespec *b,
+		      const char *branch1,
+		      const char *branch2)
 {
 	mmfile_t orig, src1, src2;
 	char *name1, *name2;
 	int merge_status;
-	const char *ll_driver_name;
-	const struct ll_merge_driver *driver;
 
 	name1 = xstrdup(mkpath("%s:%s", branch1, a->path));
 	name2 = xstrdup(mkpath("%s:%s", branch2, b->path));
@@ -981,14 +633,9 @@ static int ll_merge(mmbuffer_t *result_buf,
 	fill_mm(a->sha1, &src1);
 	fill_mm(b->sha1, &src2);
 
-	ll_driver_name = git_path_check_merge(a->path);
-	driver = find_ll_merge_driver(ll_driver_name);
-
-	if (index_only && driver->recursive)
-		driver = find_ll_merge_driver(driver->recursive);
-	merge_status = driver->fn(driver, a->path,
-				  &orig, &src1, name1, &src2, name2,
-				  result_buf);
+	merge_status = ll_merge(result_buf, a->path, &orig,
+				&src1, name1, &src2, name2,
+				index_only);
 
 	free(name1);
 	free(name2);
@@ -1029,8 +676,8 @@ static struct merge_file_info merge_file(struct diff_filespec *o,
 			mmbuffer_t result_buf;
 			int merge_status;
 
-			merge_status = ll_merge(&result_buf, o, a, b,
-						branch1, branch2);
+			merge_status = merge_3way(&result_buf, o, a, b,
+						  branch1, branch2);
 
 			if ((merge_status < 0) || !result_buf.ptr)
 				die("Failed to execute internal merge");
diff --git a/cache.h b/cache.h
index e230302623..bdefcc9188 100644
--- a/cache.h
+++ b/cache.h
@@ -543,6 +543,9 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 					unsigned long *size,
 					unsigned char *sha1_ret);
 
+extern struct object *peel_to_type(const char *name, int namelen,
+				   struct object *o, enum object_type);
+
 enum date_mode {
 	DATE_NORMAL = 0,
 	DATE_RELATIVE,
diff --git a/ll-merge.c b/ll-merge.c
new file mode 100644
index 0000000000..5ae74331bc
--- /dev/null
+++ b/ll-merge.c
@@ -0,0 +1,379 @@
+/*
+ * Low level 3-way in-core file merge.
+ *
+ * Copyright (c) 2007 Junio C Hamano
+ */
+
+#include "cache.h"
+#include "attr.h"
+#include "xdiff-interface.h"
+#include "run-command.h"
+#include "interpolate.h"
+#include "ll-merge.h"
+
+struct ll_merge_driver;
+
+typedef int (*ll_merge_fn)(const struct ll_merge_driver *,
+			   mmbuffer_t *result,
+			   const char *path,
+			   mmfile_t *orig,
+			   mmfile_t *src1, const char *name1,
+			   mmfile_t *src2, const char *name2,
+			   int virtual_ancestor);
+
+struct ll_merge_driver {
+	const char *name;
+	const char *description;
+	ll_merge_fn fn;
+	const char *recursive;
+	struct ll_merge_driver *next;
+	char *cmdline;
+};
+
+/*
+ * Built-in low-levels
+ */
+static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
+			   mmbuffer_t *result,
+			   const char *path_unused,
+			   mmfile_t *orig,
+			   mmfile_t *src1, const char *name1,
+			   mmfile_t *src2, const char *name2,
+			   int virtual_ancestor)
+{
+	/*
+	 * The tentative merge result is "ours" for the final round,
+	 * or common ancestor for an internal merge.  Still return
+	 * "conflicted merge" status.
+	 */
+	mmfile_t *stolen = virtual_ancestor ? orig : src1;
+
+	result->ptr = stolen->ptr;
+	result->size = stolen->size;
+	stolen->ptr = NULL;
+	return 1;
+}
+
+static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
+			mmbuffer_t *result,
+			const char *path_unused,
+			mmfile_t *orig,
+			mmfile_t *src1, const char *name1,
+			mmfile_t *src2, const char *name2,
+			int virtual_ancestor)
+{
+	xpparam_t xpp;
+
+	if (buffer_is_binary(orig->ptr, orig->size) ||
+	    buffer_is_binary(src1->ptr, src1->size) ||
+	    buffer_is_binary(src2->ptr, src2->size)) {
+		warning("Cannot merge binary files: %s vs. %s\n",
+			name1, name2);
+		return ll_binary_merge(drv_unused, result,
+				       path_unused,
+				       orig, src1, name1,
+				       src2, name2,
+				       virtual_ancestor);
+	}
+
+	memset(&xpp, 0, sizeof(xpp));
+	return xdl_merge(orig,
+			 src1, name1,
+			 src2, name2,
+			 &xpp, XDL_MERGE_ZEALOUS,
+			 result);
+}
+
+static int ll_union_merge(const struct ll_merge_driver *drv_unused,
+			  mmbuffer_t *result,
+			  const char *path_unused,
+			  mmfile_t *orig,
+			  mmfile_t *src1, const char *name1,
+			  mmfile_t *src2, const char *name2,
+			  int virtual_ancestor)
+{
+	char *src, *dst;
+	long size;
+	const int marker_size = 7;
+
+	int status = ll_xdl_merge(drv_unused, result, path_unused,
+				  orig, src1, NULL, src2, NULL,
+				  virtual_ancestor);
+	if (status <= 0)
+		return status;
+	size = result->size;
+	src = dst = result->ptr;
+	while (size) {
+		char ch;
+		if ((marker_size < size) &&
+		    (*src == '<' || *src == '=' || *src == '>')) {
+			int i;
+			ch = *src;
+			for (i = 0; i < marker_size; i++)
+				if (src[i] != ch)
+					goto not_a_marker;
+			if (src[marker_size] != '\n')
+				goto not_a_marker;
+			src += marker_size + 1;
+			size -= marker_size + 1;
+			continue;
+		}
+	not_a_marker:
+		do {
+			ch = *src++;
+			*dst++ = ch;
+			size--;
+		} while (ch != '\n' && size);
+	}
+	result->size = dst - result->ptr;
+	return 0;
+}
+
+#define LL_BINARY_MERGE 0
+#define LL_TEXT_MERGE 1
+#define LL_UNION_MERGE 2
+static struct ll_merge_driver ll_merge_drv[] = {
+	{ "binary", "built-in binary merge", ll_binary_merge },
+	{ "text", "built-in 3-way text merge", ll_xdl_merge },
+	{ "union", "built-in union merge", ll_union_merge },
+};
+
+static void create_temp(mmfile_t *src, char *path)
+{
+	int fd;
+
+	strcpy(path, ".merge_file_XXXXXX");
+	fd = xmkstemp(path);
+	if (write_in_full(fd, src->ptr, src->size) != src->size)
+		die("unable to write temp-file");
+	close(fd);
+}
+
+/*
+ * User defined low-level merge driver support.
+ */
+static int ll_ext_merge(const struct ll_merge_driver *fn,
+			mmbuffer_t *result,
+			const char *path,
+			mmfile_t *orig,
+			mmfile_t *src1, const char *name1,
+			mmfile_t *src2, const char *name2,
+			int virtual_ancestor)
+{
+	char temp[3][50];
+	char cmdbuf[2048];
+	struct interp table[] = {
+		{ "%O" },
+		{ "%A" },
+		{ "%B" },
+	};
+	struct child_process child;
+	const char *args[20];
+	int status, fd, i;
+	struct stat st;
+
+	if (fn->cmdline == NULL)
+		die("custom merge driver %s lacks command line.", fn->name);
+
+	result->ptr = NULL;
+	result->size = 0;
+	create_temp(orig, temp[0]);
+	create_temp(src1, temp[1]);
+	create_temp(src2, temp[2]);
+
+	interp_set_entry(table, 0, temp[0]);
+	interp_set_entry(table, 1, temp[1]);
+	interp_set_entry(table, 2, temp[2]);
+
+	interpolate(cmdbuf, sizeof(cmdbuf), fn->cmdline, table, 3);
+
+	memset(&child, 0, sizeof(child));
+	child.argv = args;
+	args[0] = "sh";
+	args[1] = "-c";
+	args[2] = cmdbuf;
+	args[3] = NULL;
+
+	status = run_command(&child);
+	if (status < -ERR_RUN_COMMAND_FORK)
+		; /* failure in run-command */
+	else
+		status = -status;
+	fd = open(temp[1], O_RDONLY);
+	if (fd < 0)
+		goto bad;
+	if (fstat(fd, &st))
+		goto close_bad;
+	result->size = st.st_size;
+	result->ptr = xmalloc(result->size + 1);
+	if (read_in_full(fd, result->ptr, result->size) != result->size) {
+		free(result->ptr);
+		result->ptr = NULL;
+		result->size = 0;
+	}
+ close_bad:
+	close(fd);
+ bad:
+	for (i = 0; i < 3; i++)
+		unlink(temp[i]);
+	return status;
+}
+
+/*
+ * merge.default and merge.driver configuration items
+ */
+static struct ll_merge_driver *ll_user_merge, **ll_user_merge_tail;
+static const char *default_ll_merge;
+
+static int read_merge_config(const char *var, const char *value)
+{
+	struct ll_merge_driver *fn;
+	const char *ep, *name;
+	int namelen;
+
+	if (!strcmp(var, "merge.default")) {
+		if (value)
+			default_ll_merge = strdup(value);
+		return 0;
+	}
+
+	/*
+	 * We are not interested in anything but "merge.<name>.variable";
+	 * especially, we do not want to look at variables such as
+	 * "merge.summary", "merge.tool", and "merge.verbosity".
+	 */
+	if (prefixcmp(var, "merge.") || (ep = strrchr(var, '.')) == var + 5)
+		return 0;
+
+	/*
+	 * Find existing one as we might be processing merge.<name>.var2
+	 * after seeing merge.<name>.var1.
+	 */
+	name = var + 6;
+	namelen = ep - name;
+	for (fn = ll_user_merge; fn; fn = fn->next)
+		if (!strncmp(fn->name, name, namelen) && !fn->name[namelen])
+			break;
+	if (!fn) {
+		fn = xcalloc(1, sizeof(struct ll_merge_driver));
+		fn->name = xmemdupz(name, namelen);
+		fn->fn = ll_ext_merge;
+		*ll_user_merge_tail = fn;
+		ll_user_merge_tail = &(fn->next);
+	}
+
+	ep++;
+
+	if (!strcmp("name", ep)) {
+		if (!value)
+			return error("%s: lacks value", var);
+		fn->description = strdup(value);
+		return 0;
+	}
+
+	if (!strcmp("driver", ep)) {
+		if (!value)
+			return error("%s: lacks value", var);
+		/*
+		 * merge.<name>.driver specifies the command line:
+		 *
+		 *	command-line
+		 *
+		 * The command-line will be interpolated with the following
+		 * tokens and is given to the shell:
+		 *
+		 *    %O - temporary file name for the merge base.
+		 *    %A - temporary file name for our version.
+		 *    %B - temporary file name for the other branches' version.
+		 *
+		 * The external merge driver should write the results in the
+		 * file named by %A, and signal that it has done with zero exit
+		 * status.
+		 */
+		fn->cmdline = strdup(value);
+		return 0;
+	}
+
+	if (!strcmp("recursive", ep)) {
+		if (!value)
+			return error("%s: lacks value", var);
+		fn->recursive = strdup(value);
+		return 0;
+	}
+
+	return 0;
+}
+
+static void initialize_ll_merge(void)
+{
+	if (ll_user_merge_tail)
+		return;
+	ll_user_merge_tail = &ll_user_merge;
+	git_config(read_merge_config);
+}
+
+static const struct ll_merge_driver *find_ll_merge_driver(const char *merge_attr)
+{
+	struct ll_merge_driver *fn;
+	const char *name;
+	int i;
+
+	initialize_ll_merge();
+
+	if (ATTR_TRUE(merge_attr))
+		return &ll_merge_drv[LL_TEXT_MERGE];
+	else if (ATTR_FALSE(merge_attr))
+		return &ll_merge_drv[LL_BINARY_MERGE];
+	else if (ATTR_UNSET(merge_attr)) {
+		if (!default_ll_merge)
+			return &ll_merge_drv[LL_TEXT_MERGE];
+		else
+			name = default_ll_merge;
+	}
+	else
+		name = merge_attr;
+
+	for (fn = ll_user_merge; fn; fn = fn->next)
+		if (!strcmp(fn->name, name))
+			return fn;
+
+	for (i = 0; i < ARRAY_SIZE(ll_merge_drv); i++)
+		if (!strcmp(ll_merge_drv[i].name, name))
+			return &ll_merge_drv[i];
+
+	/* default to the 3-way */
+	return &ll_merge_drv[LL_TEXT_MERGE];
+}
+
+static const char *git_path_check_merge(const char *path)
+{
+	static struct git_attr_check attr_merge_check;
+
+	if (!attr_merge_check.attr)
+		attr_merge_check.attr = git_attr("merge", 5);
+
+	if (git_checkattr(path, 1, &attr_merge_check))
+		return NULL;
+	return attr_merge_check.value;
+}
+
+int ll_merge(mmbuffer_t *result_buf,
+	     const char *path,
+	     mmfile_t *ancestor,
+	     mmfile_t *ours, const char *our_label,
+	     mmfile_t *theirs, const char *their_label,
+	     int virtual_ancestor)
+{
+	const char *ll_driver_name;
+	const struct ll_merge_driver *driver;
+
+	ll_driver_name = git_path_check_merge(path);
+	driver = find_ll_merge_driver(ll_driver_name);
+
+	if (virtual_ancestor && driver->recursive)
+		driver = find_ll_merge_driver(driver->recursive);
+	return driver->fn(driver, result_buf, path,
+			  ancestor,
+			  ours, our_label,
+			  theirs, their_label, virtual_ancestor);
+}
diff --git a/ll-merge.h b/ll-merge.h
new file mode 100644
index 0000000000..5388422d09
--- /dev/null
+++ b/ll-merge.h
@@ -0,0 +1,15 @@
+/*
+ * Low level 3-way in-core file merge.
+ */
+
+#ifndef LL_MERGE_H
+#define LL_MERGE_H
+
+int ll_merge(mmbuffer_t *result_buf,
+	     const char *path,
+	     mmfile_t *ancestor,
+	     mmfile_t *ours, const char *our_label,
+	     mmfile_t *theirs, const char *their_label,
+	     int virtual_ancestor);
+
+#endif
diff --git a/sha1_name.c b/sha1_name.c
index 8358ba2069..8b6c76f68e 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -422,6 +422,37 @@ static int get_nth_ancestor(const char *name, int len,
 	return 0;
 }
 
+struct object *peel_to_type(const char *name, int namelen,
+			    struct object *o, enum object_type expected_type)
+{
+	if (name && !namelen)
+		namelen = strlen(name);
+	if (!o) {
+		unsigned char sha1[20];
+		if (get_sha1_1(name, namelen, sha1))
+			return NULL;
+		o = parse_object(sha1);
+	}
+	while (1) {
+		if (!o || (!o->parsed && !parse_object(o->sha1)))
+			return NULL;
+		if (o->type == expected_type)
+			return o;
+		if (o->type == OBJ_TAG)
+			o = ((struct tag*) o)->tagged;
+		else if (o->type == OBJ_COMMIT)
+			o = &(((struct commit *) o)->tree->object);
+		else {
+			if (name)
+				error("%.*s: expected %s type, but the object "
+				      "dereferences to %s type",
+				      namelen, name, typename(expected_type),
+				      typename(o->type));
+			return NULL;
+		}
+	}
+}
+
 static int peel_onion(const char *name, int len, unsigned char *sha1)
 {
 	unsigned char outer[20];
@@ -473,32 +504,17 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		hashcpy(sha1, o->sha1);
 	}
 	else {
-		/* At this point, the syntax look correct, so
+		/*
+		 * At this point, the syntax look correct, so
 		 * if we do not get the needed object, we should
 		 * barf.
 		 */
-
-		while (1) {
-			if (!o || (!o->parsed && !parse_object(o->sha1)))
-				return -1;
-			if (o->type == expected_type) {
-				hashcpy(sha1, o->sha1);
-				return 0;
-			}
-			if (o->type == OBJ_TAG)
-				o = ((struct tag*) o)->tagged;
-			else if (o->type == OBJ_COMMIT)
-				o = &(((struct commit *) o)->tree->object);
-			else
-				return error("%.*s: expected %s type, but the object dereferences to %s type",
-					     len, name, typename(expected_type),
-					     typename(o->type));
-			if (!o)
-				return -1;
-			if (!o->parsed)
-				if (!parse_object(o->sha1))
-					return -1;
+		o = peel_to_type(name, len, o, expected_type);
+		if (o) {
+			hashcpy(sha1, o->sha1);
+			return 0;
 		}
+		return -1;
 	}
 	return 0;
 }