reset: extract reset_head() from rebase

Continue the process of lib-ifying the autostash code. In a future
commit, this will be used to implement `--autostash` in other builtins.

This patch is best viewed with `--color-moved`.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 162 insertions, 138 deletions

diff --git a/Makefile b/Makefile
index f709fc3f77..338fb55b73 100644
--- a/Makefile
+++ b/Makefile
@@ -970,6 +970,7 @@ LIB_OBJS += replace-object.o
 LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
+LIB_OBJS += reset.o
 LIB_OBJS += resolve-undo.o
 LIB_OBJS += revision.o
 LIB_OBJS += run-command.o
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 5532286142..48ef36bd10 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -27,6 +27,7 @@
 #include "branch.h"
 #include "sequencer.h"
 #include "rebase-interactive.h"
+#include "reset.h"
 
 #define DEFAULT_REFLOG_ACTION "rebase"
 
@@ -766,144 +767,6 @@ static void add_var(struct strbuf *buf, const char *name, const char *value)
 	}
 }
 
-#define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"
-
-#define RESET_HEAD_DETACH (1<<0)
-#define RESET_HEAD_HARD (1<<1)
-#define RESET_HEAD_RUN_POST_CHECKOUT_HOOK (1<<2)
-#define RESET_HEAD_REFS_ONLY (1<<3)
-#define RESET_ORIG_HEAD (1<<4)
-
-static int reset_head(struct repository *r, struct object_id *oid, const char *action,
-		      const char *switch_to_branch, unsigned flags,
-		      const char *reflog_orig_head, const char *reflog_head,
-		      const char *default_reflog_action)
-{
-	unsigned detach_head = flags & RESET_HEAD_DETACH;
-	unsigned reset_hard = flags & RESET_HEAD_HARD;
-	unsigned run_hook = flags & RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
-	unsigned refs_only = flags & RESET_HEAD_REFS_ONLY;
-	unsigned update_orig_head = flags & RESET_ORIG_HEAD;
-	struct object_id head_oid;
-	struct tree_desc desc[2] = { { NULL }, { NULL } };
-	struct lock_file lock = LOCK_INIT;
-	struct unpack_trees_options unpack_tree_opts;
-	struct tree *tree;
-	const char *reflog_action;
-	struct strbuf msg = STRBUF_INIT;
-	size_t prefix_len;
-	struct object_id *orig = NULL, oid_orig,
-		*old_orig = NULL, oid_old_orig;
-	int ret = 0, nr = 0;
-
-	if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
-		BUG("Not a fully qualified branch: '%s'", switch_to_branch);
-
-	if (!refs_only && repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
-		ret = -1;
-		goto leave_reset_head;
-	}
-
-	if ((!oid || !reset_hard) && get_oid("HEAD", &head_oid)) {
-		ret = error(_("could not determine HEAD revision"));
-		goto leave_reset_head;
-	}
-
-	if (!oid)
-		oid = &head_oid;
-
-	if (refs_only)
-		goto reset_head_refs;
-
-	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
-	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
-	unpack_tree_opts.head_idx = 1;
-	unpack_tree_opts.src_index = r->index;
-	unpack_tree_opts.dst_index = r->index;
-	unpack_tree_opts.fn = reset_hard ? oneway_merge : twoway_merge;
-	unpack_tree_opts.update = 1;
-	unpack_tree_opts.merge = 1;
-	if (!detach_head)
-		unpack_tree_opts.reset = 1;
-
-	if (repo_read_index_unmerged(r) < 0) {
-		ret = error(_("could not read index"));
-		goto leave_reset_head;
-	}
-
-	if (!reset_hard && !fill_tree_descriptor(r, &desc[nr++], &head_oid)) {
-		ret = error(_("failed to find tree of %s"),
-			    oid_to_hex(&head_oid));
-		goto leave_reset_head;
-	}
-
-	if (!fill_tree_descriptor(r, &desc[nr++], oid)) {
-		ret = error(_("failed to find tree of %s"), oid_to_hex(oid));
-		goto leave_reset_head;
-	}
-
-	if (unpack_trees(nr, desc, &unpack_tree_opts)) {
-		ret = -1;
-		goto leave_reset_head;
-	}
-
-	tree = parse_tree_indirect(oid);
-	prime_cache_tree(r, r->index, tree);
-
-	if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0) {
-		ret = error(_("could not write index"));
-		goto leave_reset_head;
-	}
-
-reset_head_refs:
-	reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
-	strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : default_reflog_action);
-	prefix_len = msg.len;
-
-	if (update_orig_head) {
-		if (!get_oid("ORIG_HEAD", &oid_old_orig))
-			old_orig = &oid_old_orig;
-		if (!get_oid("HEAD", &oid_orig)) {
-			orig = &oid_orig;
-			if (!reflog_orig_head) {
-				strbuf_addstr(&msg, "updating ORIG_HEAD");
-				reflog_orig_head = msg.buf;
-			}
-			update_ref(reflog_orig_head, "ORIG_HEAD", orig,
-				   old_orig, 0, UPDATE_REFS_MSG_ON_ERR);
-		} else if (old_orig)
-			delete_ref(NULL, "ORIG_HEAD", old_orig, 0);
-	}
-
-	if (!reflog_head) {
-		strbuf_setlen(&msg, prefix_len);
-		strbuf_addstr(&msg, "updating HEAD");
-		reflog_head = msg.buf;
-	}
-	if (!switch_to_branch)
-		ret = update_ref(reflog_head, "HEAD", oid, orig,
-				 detach_head ? REF_NO_DEREF : 0,
-				 UPDATE_REFS_MSG_ON_ERR);
-	else {
-		ret = update_ref(reflog_head, switch_to_branch, oid,
-				 NULL, 0, UPDATE_REFS_MSG_ON_ERR);
-		if (!ret)
-			ret = create_symref("HEAD", switch_to_branch,
-					    reflog_head);
-	}
-	if (run_hook)
-		run_hook_le(NULL, "post-checkout",
-			    oid_to_hex(orig ? orig : &null_oid),
-			    oid_to_hex(oid), "1", NULL);
-
-leave_reset_head:
-	strbuf_release(&msg);
-	rollback_lock_file(&lock);
-	while (nr)
-		free((void *)desc[--nr].buffer);
-	return ret;
-}
-
 static int move_to_original_branch(struct rebase_options *opts)
 {
 	struct strbuf orig_head_reflog = STRBUF_INIT, head_reflog = STRBUF_INIT;
diff --git a/reset.c b/reset.c
new file mode 100644
index 0000000000..79b683bffa
--- /dev/null
+++ b/reset.c
@@ -0,0 +1,140 @@
+#include "git-compat-util.h"
+#include "cache-tree.h"
+#include "lockfile.h"
+#include "refs.h"
+#include "reset.h"
+#include "run-command.h"
+#include "tree-walk.h"
+#include "tree.h"
+#include "unpack-trees.h"
+
+int reset_head(struct repository *r, struct object_id *oid, const char *action,
+	       const char *switch_to_branch, unsigned flags,
+	       const char *reflog_orig_head, const char *reflog_head,
+	       const char *default_reflog_action)
+{
+	unsigned detach_head = flags & RESET_HEAD_DETACH;
+	unsigned reset_hard = flags & RESET_HEAD_HARD;
+	unsigned run_hook = flags & RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
+	unsigned refs_only = flags & RESET_HEAD_REFS_ONLY;
+	unsigned update_orig_head = flags & RESET_ORIG_HEAD;
+	struct object_id head_oid;
+	struct tree_desc desc[2] = { { NULL }, { NULL } };
+	struct lock_file lock = LOCK_INIT;
+	struct unpack_trees_options unpack_tree_opts;
+	struct tree *tree;
+	const char *reflog_action;
+	struct strbuf msg = STRBUF_INIT;
+	size_t prefix_len;
+	struct object_id *orig = NULL, oid_orig,
+		*old_orig = NULL, oid_old_orig;
+	int ret = 0, nr = 0;
+
+	if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
+		BUG("Not a fully qualified branch: '%s'", switch_to_branch);
+
+	if (!refs_only && repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
+		ret = -1;
+		goto leave_reset_head;
+	}
+
+	if ((!oid || !reset_hard) && get_oid("HEAD", &head_oid)) {
+		ret = error(_("could not determine HEAD revision"));
+		goto leave_reset_head;
+	}
+
+	if (!oid)
+		oid = &head_oid;
+
+	if (refs_only)
+		goto reset_head_refs;
+
+	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
+	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
+	unpack_tree_opts.head_idx = 1;
+	unpack_tree_opts.src_index = r->index;
+	unpack_tree_opts.dst_index = r->index;
+	unpack_tree_opts.fn = reset_hard ? oneway_merge : twoway_merge;
+	unpack_tree_opts.update = 1;
+	unpack_tree_opts.merge = 1;
+	if (!detach_head)
+		unpack_tree_opts.reset = 1;
+
+	if (repo_read_index_unmerged(r) < 0) {
+		ret = error(_("could not read index"));
+		goto leave_reset_head;
+	}
+
+	if (!reset_hard && !fill_tree_descriptor(r, &desc[nr++], &head_oid)) {
+		ret = error(_("failed to find tree of %s"),
+			    oid_to_hex(&head_oid));
+		goto leave_reset_head;
+	}
+
+	if (!fill_tree_descriptor(r, &desc[nr++], oid)) {
+		ret = error(_("failed to find tree of %s"), oid_to_hex(oid));
+		goto leave_reset_head;
+	}
+
+	if (unpack_trees(nr, desc, &unpack_tree_opts)) {
+		ret = -1;
+		goto leave_reset_head;
+	}
+
+	tree = parse_tree_indirect(oid);
+	prime_cache_tree(r, r->index, tree);
+
+	if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0) {
+		ret = error(_("could not write index"));
+		goto leave_reset_head;
+	}
+
+reset_head_refs:
+	reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
+	strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : default_reflog_action);
+	prefix_len = msg.len;
+
+	if (update_orig_head) {
+		if (!get_oid("ORIG_HEAD", &oid_old_orig))
+			old_orig = &oid_old_orig;
+		if (!get_oid("HEAD", &oid_orig)) {
+			orig = &oid_orig;
+			if (!reflog_orig_head) {
+				strbuf_addstr(&msg, "updating ORIG_HEAD");
+				reflog_orig_head = msg.buf;
+			}
+			update_ref(reflog_orig_head, "ORIG_HEAD", orig,
+				   old_orig, 0, UPDATE_REFS_MSG_ON_ERR);
+		} else if (old_orig)
+			delete_ref(NULL, "ORIG_HEAD", old_orig, 0);
+	}
+
+	if (!reflog_head) {
+		strbuf_setlen(&msg, prefix_len);
+		strbuf_addstr(&msg, "updating HEAD");
+		reflog_head = msg.buf;
+	}
+	if (!switch_to_branch)
+		ret = update_ref(reflog_head, "HEAD", oid, orig,
+				 detach_head ? REF_NO_DEREF : 0,
+				 UPDATE_REFS_MSG_ON_ERR);
+	else {
+		ret = update_ref(reflog_head, switch_to_branch, oid,
+				 NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+		if (!ret)
+			ret = create_symref("HEAD", switch_to_branch,
+					    reflog_head);
+	}
+	if (run_hook)
+		run_hook_le(NULL, "post-checkout",
+			    oid_to_hex(orig ? orig : &null_oid),
+			    oid_to_hex(oid), "1", NULL);
+
+leave_reset_head:
+	strbuf_release(&msg);
+	rollback_lock_file(&lock);
+	while (nr)
+		free((void *)desc[--nr].buffer);
+	return ret;
+
+}
diff --git a/reset.h b/reset.h
new file mode 100644
index 0000000000..12f83c78e2
--- /dev/null
+++ b/reset.h
@@ -0,0 +1,20 @@
+#ifndef RESET_H
+#define RESET_H
+
+#include "hash.h"
+#include "repository.h"
+
+#define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"
+
+#define RESET_HEAD_DETACH (1<<0)
+#define RESET_HEAD_HARD (1<<1)
+#define RESET_HEAD_RUN_POST_CHECKOUT_HOOK (1<<2)
+#define RESET_HEAD_REFS_ONLY (1<<3)
+#define RESET_ORIG_HEAD (1<<4)
+
+int reset_head(struct repository *r, struct object_id *oid, const char *action,
+	       const char *switch_to_branch, unsigned flags,
+	       const char *reflog_orig_head, const char *reflog_head,
+	       const char *default_reflog_action);
+
+#endif