patch, 4 partsAdd a new test for using a custom merge strategy

Makefile, help.c, help.h

diff --git a/Makefile b/Makefile
index 52c67c1..83d79af 100644
--- a/Makefile
+++ b/Makefile
@@ -355,6 +355,7 @@ LIB_H += git-compat-util.h
 LIB_H += graph.h
 LIB_H += grep.h
 LIB_H += hash.h
+LIB_H += help.h
 LIB_H += list-objects.h
 LIB_H += ll-merge.h
 LIB_H += log-tree.h
diff --git a/help.c b/help.c
index 3cb1962..88c0d5b 100644
--- a/help.c
+++ b/help.c
@@ -9,6 +9,7 @@
 #include "common-cmds.h"
 #include "parse-options.h"
 #include "run-command.h"
+#include "help.h"
 
 static struct man_viewer_list {
 	struct man_viewer_list *next;
@@ -300,18 +301,11 @@ static inline void mput_char(char c, unsigned int num)
 		putchar(c);
 }
 
-static struct cmdnames {
-	int alloc;
-	int cnt;
-	struct cmdname {
-		size_t len;
-		char name[1];
-	} **names;
-} main_cmds, other_cmds;
+struct cmdnames main_cmds, other_cmds;
 
-static void add_cmdname(struct cmdnames *cmds, const char *name, int len)
+void add_cmdname(struct cmdnames *cmds, const char *name, int len)
 {
-	struct cmdname *ent = xmalloc(sizeof(*ent) + len);
+	struct cmdname *ent = xmalloc(sizeof(*ent) + len + 1);
 
 	ent->len = len;
 	memcpy(ent->name, name, len);
@@ -342,7 +336,7 @@ static void uniq(struct cmdnames *cmds)
 	cmds->cnt = j;
 }
 
-static void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
+void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
 {
 	int ci, cj, ei;
 	int cmp;
@@ -418,11 +412,11 @@ static int is_executable(const char *name)
 }
 
 static unsigned int list_commands_in_dir(struct cmdnames *cmds,
-					 const char *path)
+					 const char *path,
+					 const char *prefix)
 {
 	unsigned int longest = 0;
-	const char *prefix = "git-";
-	int prefix_len = strlen(prefix);
+	int prefix_len;
 	DIR *dir = opendir(path);
 	struct dirent *de;
 	struct strbuf buf = STRBUF_INIT;
@@ -430,6 +424,9 @@ static unsigned int list_commands_in_dir(struct cmdnames *cmds,
 
 	if (!dir)
 		return 0;
+	if (!prefix)
+		prefix = "git-";
+	prefix_len = strlen(prefix);
 
 	strbuf_addf(&buf, "%s/", path);
 	len = buf.len;
@@ -460,7 +457,9 @@ static unsigned int list_commands_in_dir(struct cmdnames *cmds,
 	return longest;
 }
 
-static unsigned int load_command_list(void)
+unsigned int load_command_list(const char *prefix,
+		struct cmdnames *main_cmds,
+		struct cmdnames *other_cmds)
 {
 	unsigned int longest = 0;
 	unsigned int len;
@@ -469,7 +468,7 @@ static unsigned int load_command_list(void)
 	const char *exec_path = git_exec_path();
 
 	if (exec_path)
-		longest = list_commands_in_dir(&main_cmds, exec_path);
+		longest = list_commands_in_dir(main_cmds, exec_path, prefix);
 
 	if (!env_path) {
 		fprintf(stderr, "PATH not set\n");
@@ -481,7 +480,7 @@ static unsigned int load_command_list(void)
 		if ((colon = strchr(path, PATH_SEP)))
 			*colon = 0;
 
-		len = list_commands_in_dir(&other_cmds, path);
+		len = list_commands_in_dir(other_cmds, path, prefix);
 		if (len > longest)
 			longest = len;
 
@@ -491,36 +490,38 @@ static unsigned int load_command_list(void)
 	}
 	free(paths);
 
-	qsort(main_cmds.names, main_cmds.cnt,
-	      sizeof(*main_cmds.names), cmdname_compare);
-	uniq(&main_cmds);
+	qsort(main_cmds->names, main_cmds->cnt,
+	      sizeof(*main_cmds->names), cmdname_compare);
+	uniq(main_cmds);
 
-	qsort(other_cmds.names, other_cmds.cnt,
-	      sizeof(*other_cmds.names), cmdname_compare);
-	uniq(&other_cmds);
-	exclude_cmds(&other_cmds, &main_cmds);
+	qsort(other_cmds->names, other_cmds->cnt,
+	      sizeof(*other_cmds->names), cmdname_compare);
+	uniq(other_cmds);
+	exclude_cmds(other_cmds, main_cmds);
 
 	return longest;
 }
 
-static void list_commands(void)
+void list_commands(const char *title, unsigned int longest,
+		struct cmdnames *main_cmds, struct cmdnames *other_cmds)
 {
-	unsigned int longest = load_command_list();
 	const char *exec_path = git_exec_path();
 
-	if (main_cmds.cnt) {
-		printf("available git commands in '%s'\n", exec_path);
-		printf("----------------------------");
-		mput_char('-', strlen(exec_path));
+	if (main_cmds->cnt) {
+		printf("available %s in '%s'\n", title, exec_path);
+		printf("----------------");
+		mput_char('-', strlen(title) + strlen(exec_path));
 		putchar('\n');
-		pretty_print_string_list(&main_cmds, longest);
+		pretty_print_string_list(main_cmds, longest);
 		putchar('\n');
 	}
 
-	if (other_cmds.cnt) {
-		printf("git commands available from elsewhere on your $PATH\n");
-		printf("---------------------------------------------------\n");
-		pretty_print_string_list(&other_cmds, longest);
+	if (other_cmds->cnt) {
+		printf("%s available from elsewhere on your $PATH\n", title);
+		printf("---------------------------------------");
+		mput_char('-', strlen(title));
+		putchar('\n');
+		pretty_print_string_list(other_cmds, longest);
 		putchar('\n');
 	}
 }
@@ -542,7 +543,7 @@ void list_common_cmds_help(void)
 	}
 }
 
-static int is_in_cmdlist(struct cmdnames *c, const char *s)
+int is_in_cmdlist(struct cmdnames *c, const char *s)
 {
 	int i;
 	for (i = 0; i < c->cnt; i++)
@@ -553,7 +554,6 @@ static int is_in_cmdlist(struct cmdnames *c, const char *s)
 
 static int is_git_command(const char *s)
 {
-	load_command_list();
 	return is_in_cmdlist(&main_cmds, s) ||
 		is_in_cmdlist(&other_cmds, s);
 }
@@ -698,8 +698,9 @@ int cmd_help(int argc, const char **argv, const char *prefix)
 			builtin_help_usage, 0);
 
 	if (show_all) {
+		unsigned int longest = load_command_list("git-", &main_cmds, &other_cmds);
 		printf("usage: %s\n\n", git_usage_string);
-		list_commands();
+		list_commands("git commands", longest, &main_cmds, &other_cmds);
 		printf("%s\n", git_more_info_string);
 		return 0;
 	}
diff --git a/help.h b/help.h
new file mode 100644
index 0000000..d614e54
--- /dev/null
+++ b/help.h
@@ -0,0 +1,23 @@
+#ifndef HELP_H
+#define HELP_H
+
+struct cmdnames {
+	int alloc;
+	int cnt;
+	struct cmdname {
+		size_t len;
+		char name[FLEX_ARRAY];
+	} **names;
+};
+
+unsigned int load_command_list(const char *prefix,
+		struct cmdnames *main_cmds,
+		struct cmdnames *other_cmds);
+void add_cmdname(struct cmdnames *cmds, const char *name, int len);
+/* Here we require that excludes is a sorted list. */
+void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes);
+int is_in_cmdlist(struct cmdnames *c, const char *s);
+void list_commands(const char *title, unsigned int longest,
+		struct cmdnames *main_cmds, struct cmdnames *other_cmds);
+
+#endif /* HELP_H */

diff --git a/builtin-merge.c b/builtin-merge.c
index e78fa18..99b307a 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -22,6 +22,7 @@
 #include "log-tree.h"
 #include "color.h"
 #include "rerere.h"
+#include "help.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)
@@ -77,7 +78,9 @@ static int option_parse_message(const struct option *opt,
 static struct strategy *get_strategy(const char *name)
 {
 	int i;
-	struct strbuf err;
+	struct strategy *ret;
+	static struct cmdnames main_cmds, other_cmds;
+	static int longest = 0;
 
 	if (!name)
 		return NULL;
@@ -86,12 +89,37 @@ static struct strategy *get_strategy(const char *name)
 		if (!strcmp(name, all_strategy[i].name))
 			return &all_strategy[i];
 
-	strbuf_init(&err, 0);
-	for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
-		strbuf_addf(&err, " %s", all_strategy[i].name);
-	fprintf(stderr, "Could not find merge strategy '%s'.\n", name);
-	fprintf(stderr, "Available strategies are:%s.\n", err.buf);
-	exit(1);
+	if (!longest) {
+		struct cmdnames not_strategies;
+
+		memset(&main_cmds, 0, sizeof(struct cmdnames));
+		memset(&other_cmds, 0, sizeof(struct cmdnames));
+		memset(&not_strategies, 0, sizeof(struct cmdnames));
+		longest = load_command_list("git-merge-", &main_cmds,
+				&other_cmds);
+		for (i = 0; i < main_cmds.cnt; i++) {
+			int j, found = 0;
+			struct cmdname *ent = main_cmds.names[i];
+			for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
+				if (!strncmp(ent->name, all_strategy[j].name, ent->len)
+						&& !all_strategy[j].name[ent->len])
+					found = 1;
+			if (!found)
+				add_cmdname(&not_strategies, ent->name, ent->len);
+			exclude_cmds(&main_cmds, &not_strategies);
+		}
+	}
+	if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
+
+		fprintf(stderr, "Could not find merge strategy '%s'.\n\n", name);
+		list_commands("strategies", longest, &main_cmds, &other_cmds);
+		exit(1);
+	}
+
+	ret = xmalloc(sizeof(struct strategy));
+	memset(ret, 0, sizeof(struct strategy));
+	ret->name = xstrdup(name);
+	return ret;
 }
 
 static void append_strategy(struct strategy *s)

diff --git a/t/t7606-merge-custom.sh b/t/t7606-merge-custom.sh
new file mode 100755
index 0000000..13e8ff5
--- /dev/null
+++ b/t/t7606-merge-custom.sh
@@ -0,0 +1,46 @@
+#!/bin/sh
+
+test_description='git-merge
+
+Testing a custom strategy.'
+
+. ./test-lib.sh
+
+cat > git-merge-theirs << EOF
+#!/bin/sh
+eval git read-tree --reset -u \\\$\$#
+EOF
+chmod +x git-merge-theirs
+PATH=.:$PATH
+export PATH
+
+test_expect_success 'setup' '
+	echo c0 > c0.c &&
+	git add c0.c &&
+	git commit -m c0 &&
+	git tag c0 &&
+	echo c1 > c1.c &&
+	git add c1.c &&
+	git commit -m c1 &&
+	git tag c1 &&
+	git reset --hard c0 &&
+	echo c2 > c2.c &&
+	git add c2.c &&
+	git commit -m c2 &&
+	git tag c2
+'
+
+test_expect_success 'merge c2 with a custom strategy' '
+	git reset --hard c1 &&
+	git merge -s theirs c2 &&
+	test "$(git rev-parse c1)" != "$(git rev-parse HEAD)" &&
+	test "$(git rev-parse c1)" = "$(git rev-parse HEAD^1)" &&
+	test "$(git rev-parse c2)" = "$(git rev-parse HEAD^2)" &&
+	test "$(git rev-parse c2^{tree})" = "$(git rev-parse HEAD^{tree})" &&
+	git diff --exit-code &&
+	test -f c0.c &&
+	test ! -f c1.c &&
+	test -f c2.c
+'
+
+test_done

diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 5eeb6c2..0329aee 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -230,6 +230,10 @@ test_expect_success 'test option parsing' '
 	test_must_fail git merge
 '
 
+test_expect_success 'reject non-strategy with a git-merge-foo name' '
+	test_must_fail git merge -s index c1
+'
+
 test_expect_success 'merge c0 with c1' '
 	git reset --hard c0 &&
 	git merge c1 &&