pull: implement fetch + merge

Implement the fetch + merge functionality of git-pull, by first running
git-fetch with the repo and refspecs provided on the command line, then
running git-merge on FETCH_HEAD to merge the fetched refs into the
current branch.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pull.c

@@ -9,17 +9,72 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "exec_cmd.h"
+#include "run-command.h"
 
 static const char * const pull_usage[] = {
+	N_("git pull [options] [<repository> [<refspec>...]]"),
 	NULL
 };
 
 static struct option pull_options[] = {
 	OPT_END()
 };
 
+/**
+ * Parses argv into [<repo> [<refspecs>...]], returning their values in `repo`
+ * as a string and `refspecs` as a null-terminated array of strings. If `repo`
+ * is not provided in argv, it is set to NULL.
+ */
+static void parse_repo_refspecs(int argc, const char **argv, const char **repo,
+		const char ***refspecs)
+{
+	if (argc > 0) {
+		*repo = *argv++;
+		argc--;
+	} else
+		*repo = NULL;
+	*refspecs = argv;
+}
+
+/**
+ * Runs git-fetch, returning its exit status. `repo` and `refspecs` are the
+ * repository and refspecs to fetch, or NULL if they are not provided.
+ */
+static int run_fetch(const char *repo, const char **refspecs)
+{
+	struct argv_array args = ARGV_ARRAY_INIT;
+	int ret;
+
+	argv_array_pushl(&args, "fetch", "--update-head-ok", NULL);
+	if (repo) {
+		argv_array_push(&args, repo);
+		argv_array_pushv(&args, refspecs);
+	} else if (*refspecs)
+		die("BUG: refspecs without repo?");
+	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
+	argv_array_clear(&args);
+	return ret;
+}
+
+/**
+ * Runs git-merge, returning its exit status.
+ */
+static int run_merge(void)
+{
+	int ret;
+	struct argv_array args = ARGV_ARRAY_INIT;
+
+	argv_array_pushl(&args, "merge", NULL);
+	argv_array_push(&args, "FETCH_HEAD");
+	ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
+	argv_array_clear(&args);
+	return ret;
+}
+
 int cmd_pull(int argc, const char **argv, const char *prefix)
 {
+	const char *repo, **refspecs;
+
 	if (!getenv("_GIT_USE_BUILTIN_PULL")) {
 		const char *path = mkpath("%s/git-pull", git_exec_path());
 
@@ -29,5 +84,10 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 	argc = parse_options(argc, argv, prefix, pull_options, pull_usage, 0);
 
-	return 0;
+	parse_repo_refspecs(argc, argv, &repo, &refspecs);
+
+	if (run_fetch(repo, refspecs))
+		return 1;
+
+	return run_merge();
 }