diff mbox series

[v3,11/19] reset: extract reset_head() from rebase

Message ID a14a2e0849fea91c6c41cf71b8d049123bea0c6d.1584782450.git.liu.denton@gmail.com (mailing list archive)
State New, archived
Headers show
Series merge: learn --autostash | expand

Commit Message

Denton Liu March 21, 2020, 9:21 a.m. UTC 
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>
---
 Makefile         |   1 +
 builtin/rebase.c | 139 +---------------------------------------------
 reset.c          | 140 +++++++++++++++++++++++++++++++++++++++++++++++
 reset.h          |  20 +++++++
 4 files changed, 162 insertions(+), 138 deletions(-)
 create mode 100644 reset.c
 create mode 100644 reset.h

Comments

Phillip Wood April 2, 2020, 3:04 p.m. UTC | #1 
Hi Denton

On 21/03/2020 09:21, Denton Liu wrote:
> 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`.

Indeed! It looks good. Looking ahead I hope we can use this to avoid 
forking 'git checkout' in sequencer.c

Best Wishes

Phillip

> 
> Signed-off-by: Denton Liu <liu.denton@gmail.com>
> ---
>   Makefile         |   1 +
>   builtin/rebase.c | 139 +---------------------------------------------
>   reset.c          | 140 +++++++++++++++++++++++++++++++++++++++++++++++
>   reset.h          |  20 +++++++
>   4 files changed, 162 insertions(+), 138 deletions(-)
>   create mode 100644 reset.c
>   create mode 100644 reset.h
> 
> 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 52eb45b6c4..caff67b00d 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
>
diff mbox series

Patch

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 52eb45b6c4..caff67b00d 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