Make "git reset" a builtin.

This replaces the script "git-reset.sh" with "builtin-reset.c".

A few git commands used in the script are called from the builtin also:
"ls-files" to check for unmerged files, "read-tree" for resetting
the index file in "mixed" and "hard" resets, and "update-index" to
refresh at the end in the "mixed" reset and also for the option that
gets selected paths into the index.

The reset option with paths was implemented by Johannes Schindelin.

Since the option that gets selected paths into the index is not
a "reset" like the others because it does not change the HEAD at all,
now the command is showing a warning when the "--mixed" option
is supplied for that purpose.

The following table shows the behaviour of "git reset" for
the different supported options, where X means "changing"
the HEAD, index or working tree:

reset:  --soft  --mixed  --hard  -- <paths>
HEAD       X       X        X        -
index      -       X        X        X
files      -       -        X        -

Signed-off-by: Carlos Rica <jasampler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 279 insertions, 0 deletions

diff --git a/builtin-reset.c b/builtin-reset.c
new file mode 100644
index 0000000000..99d5c082a6
--- /dev/null
+++ b/builtin-reset.c
@@ -0,0 +1,279 @@
+/*
+ * "git reset" builtin command
+ *
+ * Copyright (c) 2007 Carlos Rica
+ *
+ * Based on git-reset.sh, which is
+ *
+ * Copyright (c) 2005, 2006 Linus Torvalds and Junio C Hamano
+ */
+#include "cache.h"
+#include "tag.h"
+#include "object.h"
+#include "commit.h"
+#include "run-command.h"
+#include "refs.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "tree.h"
+
+static const char builtin_reset_usage[] =
+"git-reset [--mixed | --soft | --hard]  [<commit-ish>] [ [--] <paths>...]";
+
+static char *args_to_str(const char **argv)
+{
+	char *buf = NULL;
+	unsigned long len, space = 0, nr = 0;
+
+	for (; *argv; argv++) {
+		len = strlen(*argv);
+		ALLOC_GROW(buf, nr + 1 + len, space);
+		if (nr)
+			buf[nr++] = ' ';
+		memcpy(buf + nr, *argv, len);
+		nr += len;
+	}
+	ALLOC_GROW(buf, nr + 1, space);
+	buf[nr] = '\0';
+
+	return buf;
+}
+
+static inline int is_merge(void)
+{
+	return !access(git_path("MERGE_HEAD"), F_OK);
+}
+
+static int unmerged_files(void)
+{
+	char b;
+	ssize_t len;
+	struct child_process cmd;
+	const char *argv_ls_files[] = {"ls-files", "--unmerged", NULL};
+
+	memset(&cmd, 0, sizeof(cmd));
+	cmd.argv = argv_ls_files;
+	cmd.git_cmd = 1;
+	cmd.out = -1;
+
+	if (start_command(&cmd))
+		die("Could not run sub-command: git ls-files");
+
+	len = xread(cmd.out, &b, 1);
+	if (len < 0)
+		die("Could not read output from git ls-files: %s",
+						strerror(errno));
+	finish_command(&cmd);
+
+	return len;
+}
+
+static int reset_index_file(const unsigned char *sha1, int is_hard_reset)
+{
+	int i = 0;
+	const char *args[6];
+
+	args[i++] = "read-tree";
+	args[i++] = "-v";
+	args[i++] = "--reset";
+	if (is_hard_reset)
+		args[i++] = "-u";
+	args[i++] = sha1_to_hex(sha1);
+	args[i] = NULL;
+
+	return run_command_v_opt(args, RUN_GIT_CMD);
+}
+
+static void print_new_head_line(struct commit *commit)
+{
+	const char *hex, *dots = "...", *body;
+
+	hex = find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV);
+	if (!hex) {
+		hex = sha1_to_hex(commit->object.sha1);
+		dots = "";
+	}
+	printf("HEAD is now at %s%s", hex, dots);
+	body = strstr(commit->buffer, "\n\n");
+	if (body) {
+		const char *eol;
+		size_t len;
+		body += 2;
+		eol = strchr(body, '\n');
+		len = eol ? eol - body : strlen(body);
+		printf(" %.*s\n", (int) len, body);
+	}
+	else
+		printf("\n");
+}
+
+static int update_index_refresh(void)
+{
+	const char *argv_update_index[] = {"update-index", "--refresh", NULL};
+	return run_command_v_opt(argv_update_index, RUN_GIT_CMD);
+}
+
+static void update_index_from_diff(struct diff_queue_struct *q,
+		struct diff_options *opt, void *data)
+{
+	int i;
+
+	/* do_diff_cache() mangled the index */
+	discard_cache();
+	read_cache();
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filespec *one = q->queue[i]->one;
+		if (one->mode) {
+			struct cache_entry *ce;
+			ce = make_cache_entry(one->mode, one->sha1, one->path,
+				0, 0);
+			add_cache_entry(ce, ADD_CACHE_OK_TO_ADD |
+				ADD_CACHE_OK_TO_REPLACE);
+		} else
+			remove_file_from_cache(one->path);
+	}
+}
+
+static int read_from_tree(const char *prefix, const char **argv,
+		unsigned char *tree_sha1)
+{
+        struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
+	int index_fd;
+	struct diff_options opt;
+
+	memset(&opt, 0, sizeof(opt));
+	diff_tree_setup_paths(get_pathspec(prefix, (const char **)argv), &opt);
+	opt.output_format = DIFF_FORMAT_CALLBACK;
+	opt.format_callback = update_index_from_diff;
+
+	index_fd = hold_locked_index(lock, 1);
+	read_cache();
+	if (do_diff_cache(tree_sha1, &opt))
+		return 1;
+	diffcore_std(&opt);
+	diff_flush(&opt);
+	return write_cache(index_fd, active_cache, active_nr) ||
+		close(index_fd) ||
+		commit_locked_index(lock);
+}
+
+static void prepend_reflog_action(const char *action, char *buf, size_t size)
+{
+	const char *sep = ": ";
+	const char *rla = getenv("GIT_REFLOG_ACTION");
+	if (!rla)
+		rla = sep = "";
+	if (snprintf(buf, size, "%s%s%s", rla, sep, action) >= size)
+		warning("Reflog action message too long: %.*s...", 50, buf);
+}
+
+enum reset_type { MIXED, SOFT, HARD, NONE };
+static char *reset_type_names[] = { "mixed", "soft", "hard", NULL };
+
+int cmd_reset(int argc, const char **argv, const char *prefix)
+{
+	int i = 1, reset_type = NONE, update_ref_status = 0;
+	const char *rev = "HEAD";
+	unsigned char sha1[20], *orig = NULL, sha1_orig[20],
+				*old_orig = NULL, sha1_old_orig[20];
+	struct commit *commit;
+	char *reflog_action, msg[1024];
+
+	git_config(git_default_config);
+
+	reflog_action = args_to_str(argv);
+	setenv("GIT_REFLOG_ACTION", reflog_action, 0);
+
+	if (i < argc) {
+		if (!strcmp(argv[i], "--mixed")) {
+			reset_type = MIXED;
+			i++;
+		}
+		else if (!strcmp(argv[i], "--soft")) {
+			reset_type = SOFT;
+			i++;
+		}
+		else if (!strcmp(argv[i], "--hard")) {
+			reset_type = HARD;
+			i++;
+		}
+	}
+
+	if (i < argc && argv[i][0] != '-')
+		rev = argv[i++];
+
+	if (get_sha1(rev, sha1))
+		die("Failed to resolve '%s' as a valid ref.", rev);
+
+	commit = lookup_commit_reference(sha1);
+	if (!commit)
+		die("Could not parse object '%s'.", rev);
+	hashcpy(sha1, commit->object.sha1);
+
+	if (i < argc && !strcmp(argv[i], "--"))
+		i++;
+	else if (i < argc && argv[i][0] == '-')
+		usage(builtin_reset_usage);
+
+	/* git reset tree [--] paths... can be used to
+	 * load chosen paths from the tree into the index without
+	 * affecting the working tree nor HEAD. */
+	if (i < argc) {
+		if (reset_type == MIXED)
+			warning("--mixed option is deprecated with paths.");
+		else if (reset_type != NONE)
+			die("Cannot do %s reset with paths.",
+					reset_type_names[reset_type]);
+		if (read_from_tree(prefix, argv + i, sha1))
+			return 1;
+		return update_index_refresh() ? 1 : 0;
+	}
+	if (reset_type == NONE)
+		reset_type = MIXED; /* by default */
+
+	/* Soft reset does not touch the index file nor the working tree
+	 * at all, but requires them in a good order.  Other resets reset
+	 * the index file to the tree object we are switching to. */
+	if (reset_type == SOFT) {
+		if (is_merge() || unmerged_files())
+			die("Cannot do a soft reset in the middle of a merge.");
+	}
+	else if (reset_index_file(sha1, (reset_type == HARD)))
+		die("Could not reset index file to revision '%s'.", rev);
+
+	/* Any resets update HEAD to the head being switched to,
+	 * saving the previous head in ORIG_HEAD before. */
+	if (!get_sha1("ORIG_HEAD", sha1_old_orig))
+		old_orig = sha1_old_orig;
+	if (!get_sha1("HEAD", sha1_orig)) {
+		orig = sha1_orig;
+		prepend_reflog_action("updating ORIG_HEAD", msg, sizeof(msg));
+		update_ref(msg, "ORIG_HEAD", orig, old_orig, 0, MSG_ON_ERR);
+	}
+	else if (old_orig)
+		delete_ref("ORIG_HEAD", old_orig);
+	prepend_reflog_action("updating HEAD", msg, sizeof(msg));
+	update_ref_status = update_ref(msg, "HEAD", sha1, orig, 0, MSG_ON_ERR);
+
+	switch (reset_type) {
+	case HARD:
+		if (!update_ref_status)
+			print_new_head_line(commit);
+		break;
+	case SOFT: /* Nothing else to do. */
+		break;
+	case MIXED: /* Report what has not been updated. */
+		update_index_refresh();
+		break;
+	}
+
+	unlink(git_path("MERGE_HEAD"));
+	unlink(git_path("rr-cache/MERGE_RR"));
+	unlink(git_path("MERGE_MSG"));
+	unlink(git_path("SQUASH_MSG"));
+
+	free(reflog_action);
+
+	return update_ref_status;
+}