difftool: prepare "diff" cmdline in cmd_difftool()

We call into either run_dir_diff() or run_file_diff(), each of which
sets up a child argv starting with "diff" and some hard-coded options
(depending on which mode we're using). Let's extract that logic into the
caller, which will make it easier to modify the options for cases which
affect both functions.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/difftool.c

@@ -331,7 +331,6 @@ static int checkout_path(unsigned mode, struct object_id *oid,
 }
 
 static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
-			int argc, const char **argv,
 			struct child_process *child)
 {
 	char tmpdir[PATH_MAX];
@@ -393,10 +392,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 	child->clean_on_exit = 1;
 	child->dir = prefix;
 	child->out = -1;
-	strvec_pushl(&child->args, "diff", "--raw", "--no-abbrev", "-z",
-		     NULL);
-	for (i = 0; i < argc; i++)
-		strvec_push(&child->args, argv[i]);
 	if (start_command(child))
 		die("could not obtain raw diff");
 	fp = xfdopen(child->out, "r");
@@ -683,7 +678,6 @@ static int run_file_diff(int prompt, const char *prefix,
 		env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
 
 
-	strvec_push(&args, "diff");
 	for (i = 0; i < argc; i++)
 		strvec_push(&args, argv[i]);
 	return run_command_v_opt_cd_env(args.v, RUN_GIT_CMD, prefix, env);
@@ -769,7 +763,12 @@ int cmd_difftool(int argc, const char **argv, const char *prefix)
 	 * will invoke a separate instance of 'git-difftool--helper' for
 	 * each file that changed.
 	 */
+	strvec_push(&child.args, "diff");
+	if (dir_diff)
+		strvec_pushl(&child.args, "--raw", "--no-abbrev", "-z", NULL);
+	strvec_pushv(&child.args, argv);
+
 	if (dir_diff)
-		return run_dir_diff(extcmd, symlinks, prefix, argc, argv, &child);
-	return run_file_diff(prompt, prefix, argc, argv);
+		return run_dir_diff(extcmd, symlinks, prefix, &child);
+	return run_file_diff(prompt, prefix, child.args.nr, child.args.v);
 }