Git message editing.

commit.c

static int prepare_to_commit(const char *index_file, const char *prefix,
			     struct wt_status *s)
{
	struct stat statbuf;
	int commitable, saved_color_setting;
	struct strbuf sb = STRBUF_INIT;
	char *buffer;
	FILE *fp;
	const char *hook_arg1 = NULL;
	const char *hook_arg2 = NULL;
	int ident_shown = 0;

	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
		return 0;

	if (message.len) {
		strbuf_addbuf(&sb, &message);
		hook_arg1 = "message";
	} else if (logfile && !strcmp(logfile, "-")) {
		if (isatty(0))
			fprintf(stderr, "(reading log message from standard input)\n");
		if (strbuf_read(&sb, 0, 0) < 0)
			die_errno("could not read log from standard input");
		hook_arg1 = "message";
	} else if (logfile) {
		if (strbuf_read_file(&sb, logfile, 0) < 0)
			die_errno("could not read log file '%s'",
				  logfile);
		hook_arg1 = "message";
	} else if (use_message) {
		buffer = strstr(use_message_buffer, "\n\n");
		if (!buffer || buffer[2] == '\0')
			die("commit has empty message");
		strbuf_add(&sb, buffer + 2, strlen(buffer + 2));
		hook_arg1 = "commit";
		hook_arg2 = use_message;
	} else if (!stat(git_path("MERGE_MSG"), &statbuf)) {
		if (strbuf_read_file(&sb, git_path("MERGE_MSG"), 0) < 0)
			die_errno("could not read MERGE_MSG");
		hook_arg1 = "merge";
	} else if (!stat(git_path("SQUASH_MSG"), &statbuf)) {
		if (strbuf_read_file(&sb, git_path("SQUASH_MSG"), 0) < 0)
			die_errno("could not read SQUASH_MSG");
		hook_arg1 = "squash";
	} else if (template_file && !stat(template_file, &statbuf)) {
		if (strbuf_read_file(&sb, template_file, 0) < 0)
			die_errno("could not read '%s'", template_file);
		hook_arg1 = "template";
	}

	/*
	 * This final case does not modify the template message,
	 * it just sets the argument to the prepare-commit-msg hook.
	 */
	else if (in_merge)
		hook_arg1 = "merge";

	fp = fopen(git_path(commit_editmsg), "w");
	if (fp == NULL)
		die_errno("could not open '%s'", git_path(commit_editmsg));

	if (cleanup_mode != CLEANUP_NONE)
		stripspace(&sb, 0);

	if (signoff) {
		struct strbuf sob = STRBUF_INIT;
		int i;

		strbuf_addstr(&sob, sign_off_header);
		strbuf_addstr(&sob, fmt_name(getenv("GIT_COMMITTER_NAME"),
					     getenv("GIT_COMMITTER_EMAIL")));
		strbuf_addch(&sob, '\n');
		for (i = sb.len - 1; i > 0 && sb.buf[i - 1] != '\n'; i--)
			; /* do nothing */
		if (prefixcmp(sb.buf + i, sob.buf)) {
			if (!i || !ends_rfc2822_footer(&sb))
				strbuf_addch(&sb, '\n');
			strbuf_addbuf(&sb, &sob);
		}
		strbuf_release(&sob);
	}

	if (fwrite(sb.buf, 1, sb.len, fp) < sb.len)
		die_errno("could not write commit template");

	strbuf_release(&sb);

	determine_author_info();

	/* This checks if committer ident is explicitly given */
	git_committer_info(0);
	if (use_editor && include_status) {
		char *author_ident;
		const char *committer_ident;

		if (in_merge)
			fprintf(fp,
				"#\n"
				"# It looks like you may be committing a MERGE.\n"
				"# If this is not correct, please remove the file\n"
				"#	%s\n"
				"# and try again.\n"
				"#\n",
				git_path("MERGE_HEAD"));

		fprintf(fp,
			"\n"
			"# Please enter the commit message for your changes.");
		if (cleanup_mode == CLEANUP_ALL)
			fprintf(fp,
				" Lines starting\n"
				"# with '#' will be ignored, and an empty"
				" message aborts the commit.\n");
		else /* CLEANUP_SPACE, that is. */
			fprintf(fp,
				" Lines starting\n"
				"# with '#' will be kept; you may remove them"
				" yourself if you want to.\n"
				"# An empty message aborts the commit.\n");
		if (only_include_assumed)
			fprintf(fp, "# %s\n", only_include_assumed);

		author_ident = xstrdup(fmt_name(author_name, author_email));
		committer_ident = fmt_name(getenv("GIT_COMMITTER_NAME"),
					   getenv("GIT_COMMITTER_EMAIL"));
		if (strcmp(author_ident, committer_ident))
			fprintf(fp,
				"%s"
				"# Author:    %s\n",
				ident_shown++ ? "" : "#\n",
				author_ident);
		free(author_ident);

		if (!user_ident_sufficiently_given())
			fprintf(fp,
				"%s"
				"# Committer: %s\n",
				ident_shown++ ? "" : "#\n",
				committer_ident);

		if (ident_shown)
			fprintf(fp, "#\n");

		saved_color_setting = s->use_color;
		s->use_color = 0;
		commitable = run_status(fp, index_file, prefix, 1, s);
		s->use_color = saved_color_setting;
	} else {
		unsigned char sha1[20];
		const char *parent = "HEAD";

		if (!active_nr && read_cache() < 0)
			die("Cannot read index");

		if (amend)
			parent = "HEAD^1";

		if (get_sha1(parent, sha1))
			commitable = !!active_nr;
		else
			commitable = index_differs_from(parent, 0);
	}

	fclose(fp);

	if (!commitable && !in_merge && !allow_empty &&
	    !(amend && is_a_merge(head_sha1))) {
		run_status(stdout, index_file, prefix, 0, s);
		return 0;
	}

	/*
	 * Re-read the index as pre-commit hook could have updated it,
	 * and write it out as a tree.  We must do this before we invoke
	 * the editor and after we invoke run_status above.
	 */
	discard_cache();
	read_cache_from(index_file);
	if (!active_cache_tree)
		active_cache_tree = cache_tree();
	if (cache_tree_update(active_cache_tree,
			      active_cache, active_nr, 0, 0) < 0) {
		error("Error building trees");
		return 0;
	}

	if (run_hook(index_file, "prepare-commit-msg",
		     git_path(commit_editmsg), hook_arg1, hook_arg2, NULL))
		return 0;

	if (use_editor) {
		char index[PATH_MAX];
		const char *env[2] = { index, NULL };
		snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
		if (launch_editor(git_path(commit_editmsg), NULL, env)) {
			fprintf(stderr,
			"Please supply the message using either -m or -F option.\n");
			exit(1);
		}
	}

	if (!no_verify &&
	    run_hook(index_file, "commit-msg", git_path(commit_editmsg), NULL)) {
		return 0;
	}

	return 1;
}

editor.c

#ifndef DEFAULT_EDITOR
#define DEFAULT_EDITOR "vi"
#endif

const char *git_editor(void)
{
	const char *editor = getenv("GIT_EDITOR");
	const char *terminal = getenv("TERM");
	int terminal_is_dumb = !terminal || !strcmp(terminal, "dumb");

	if (!editor && editor_program)
		editor = editor_program;
	if (!editor && !terminal_is_dumb)
		editor = getenv("VISUAL");
	if (!editor)
		editor = getenv("EDITOR");

	if (!editor && terminal_is_dumb)
		return NULL;

	if (!editor)
		editor = DEFAULT_EDITOR;

	return editor;
}

int launch_editor(const char *path, struct strbuf *buffer, const char *const *env)
{
	const char *editor = git_editor();

	if (!editor)
		return error("Terminal is dumb, but EDITOR unset");

	if (strcmp(editor, ":")) {
		const char *args[] = { editor, path, NULL };

		if (run_command_v_opt_cd_env(args, RUN_USING_SHELL, NULL, env))
			return error("There was a problem with the editor '%s'.",
					editor);
	}

	if (!buffer)
		return 0;
	if (strbuf_read_file(buffer, path, 0) < 0)
		return error("could not read file '%s': %s",
				path, strerror(errno));
	return 0;
}

path.c

/*
 * I'm tired of doing "vsnprintf()" etc just to open a
 * file, so here's a "return static buffer with printf"
 * interface for paths.
 *
 * It's obviously not thread-safe. Sue me. But it's quite
 * useful for doing things like
 *
 *   f = open(mkpath("%s/%s.git", base, name), O_RDONLY);
 *
 * which is what it's designed for.
 */

/*
 * snip
 */

char *git_path(const char *fmt, ...)
{
	const char *git_dir = get_git_dir();
	char *pathname = get_pathname();
	va_list args;
	unsigned len;

	len = strlen(git_dir);
	if (len > PATH_MAX-100)
		return bad_path;
	memcpy(pathname, git_dir, len);
	if (len && git_dir[len-1] != '/')
		pathname[len++] = '/';
	va_start(args, fmt);
	len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
	va_end(args);
	if (len >= PATH_MAX)
		return bad_path;
	return cleanup_path(pathname);
}