Re: [RFC PATCH 4/7] autostash: extract reset_head() from rebase

> Begin the process of lib-ifying the autostash code. In a future commit,
> 
> This patch is best viewed with `--color-moved` and
> `--color-moved-ws=allow-indentation-change`.
> this will be used to implement `--autostash` in other builtins.
> 
> Signed-off-by: Denton Liu <liu.denton@gmail.com>
> ---
>   autostash.c      | 137 +++++++++++++++++++++++++++++++++++++++++++++++
>   autostash.h      |  12 +++++
>   builtin/rebase.c | 137 -----------------------------------------------
>   3 files changed, 149 insertions(+), 137 deletions(-)
> 
> diff --git a/autostash.c b/autostash.c
> index 62ec7a7c80..eb58e0c8a4 100644
> --- a/autostash.c
> +++ b/autostash.c
> @@ -1,9 +1,17 @@
> +#define USE_THE_INDEX_COMPATIBILITY_MACROS

> +
>   #include "git-compat-util.h"
>   #include "autostash.h"
> +#include "cache-tree.h"
>   #include "dir.h"
>   #include "gettext.h"
> +#include "lockfile.h"
> +#include "refs.h"
>   #include "run-command.h"
>   #include "strbuf.h"
> +#include "tree-walk.h"
> +#include "tree.h"
> +#include "unpack-trees.h"
>   
>   int read_one(const char *path, struct strbuf *buf)
>   {
> @@ -13,6 +21,135 @@ int read_one(const char *path, struct strbuf *buf)
>   	return 0;
>   }
>   
> +int reset_head(struct object_id *oid, const char *action,
> +	       const char *switch_to_branch, unsigned flags,
> +	       const char *reflog_orig_head, const char *reflog_head)
> +{
> +	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 && hold_locked_index(&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 = the_repository->index;
> +	unpack_tree_opts.dst_index = the_repository->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(the_repository) < 0) {
> +		ret = error(_("could not read index"));
> +		goto leave_reset_head;
> +	}
> +
> +	if (!reset_hard && !fill_tree_descriptor(the_repository, &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(the_repository, &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(the_repository, the_repository->index, tree);
> +
> +	if (write_locked_index(the_repository->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 : "rebase");
> +	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;
> +}
> +
>   int apply_autostash(const char *path)
>   {
>   	struct strbuf autostash = STRBUF_INIT;
> diff --git a/autostash.h b/autostash.h
> index 5f4e4bd22c..1406638166 100644
> --- a/autostash.h
> +++ b/autostash.h
> @@ -6,6 +6,18 @@
>   /* Read one file, then strip line endings */
>   int read_one(const char *path, struct strbuf *buf);
>   
> +#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 object_id *oid, const char *action,
> +	       const char *switch_to_branch, unsigned flags,
> +	       const char *reflog_orig_head, const char *reflog_head);
> +
>   int apply_autostash(const char *path);
>   
>   #endif
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index 661928d427..c3165896cc 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -734,143 +734,6 @@ 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 object_id *oid, const char *action,
> -		      const char *switch_to_branch, unsigned flags,
> -		      const char *reflog_orig_head, const char *reflog_head)
> -{
> -	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 && hold_locked_index(&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 = the_repository->index;
> -	unpack_tree_opts.dst_index = the_repository->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(the_repository) < 0) {
> -		ret = error(_("could not read index"));
> -		goto leave_reset_head;
> -	}
> -
> -	if (!reset_hard && !fill_tree_descriptor(the_repository, &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(the_repository, &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(the_repository, the_repository->index, tree);
> -
> -	if (write_locked_index(the_repository->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 : "rebase");
> -	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;
>