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git/sequencer.h
Elijah Newren e98c4269c8 rebase (interactive-backend): fix handling of commits that become empty
As established in the previous commit and commit b00bf1c9a8
(git-rebase: make --allow-empty-message the default, 2018-06-27), the
behavior for rebase with different backends in various edge or corner
cases is often more happenstance than design.  This commit addresses
another such corner case: commits which "become empty".

A careful reader may note that there are two types of commits which would
become empty due to a rebase:

  * [clean cherry-pick] Commits which are clean cherry-picks of upstream
    commits, as determined by `git log --cherry-mark ...`.  Re-applying
    these commits would result in an empty set of changes and a
    duplicative commit message; i.e. these are commits that have
    "already been applied" upstream.

  * [become empty] Commits which are not empty to start, are not clean
    cherry-picks of upstream commits, but which still become empty after
    being rebased.  This happens e.g. when a commit has changes which
    are a strict subset of the changes in an upstream commit, or when
    the changes of a commit can be found spread across or among several
    upstream commits.

Clearly, in both cases the changes in the commit in question are found
upstream already, but the commit message may not be in the latter case.

When cherry-mark can determine a commit is already upstream, then
because of how cherry-mark works this means the upstream commit message
was about the *exact* same set of changes.  Thus, the commit messages
can be assumed to be fully interchangeable (and are in fact likely to be
completely identical).  As such, the clean cherry-pick case represents a
case when there is no information to be gained by keeping the extra
commit around.  All rebase types have always dropped these commits, and
no one to my knowledge has ever requested that we do otherwise.

For many of the become empty cases (and likely even most), we will also
be able to drop the commit without loss of information -- but this isn't
quite always the case.  Since these commits represent cases that were
not clean cherry-picks, there is no upstream commit message explaining
the same set of changes.  Projects with good commit message hygiene will
likely have the explanation from our commit message contained within or
spread among the relevant upstream commits, but not all projects run
that way.  As such, the commit message of the commit being rebased may
have reasoning that suggests additional changes that should be made to
adapt to the new base, or it may have information that someone wants to
add as a note to another commit, or perhaps someone even wants to create
an empty commit with the commit message as-is.

Junio commented on the "become-empty" types of commits as follows[1]:

    WRT a change that ends up being empty (as opposed to a change that
    is empty from the beginning), I'd think that the current behaviour
    is desireable one.  "am" based rebase is solely to transplant an
    existing history and want to stop much less than "interactive" one
    whose purpose is to polish a series before making it publishable,
    and asking for confirmation ("this has become empty--do you want to
    drop it?") is more appropriate from the workflow point of view.

[1] https://lore.kernel.org/git/xmqqfu1fswdh.fsf@gitster-ct.c.googlers.com/

I would simply add that his arguments for "am"-based rebases actually
apply to all non-explicitly-interactive rebases.  Also, since we are
stating that different cases should have different defaults, it may be
worth providing a flag to allow users to select which behavior they want
for these commits.

Introduce a new command line flag for selecting the desired behavior:
    --empty={drop,keep,ask}
with the definitions:
    drop: drop commits which become empty
    keep: keep commits which become empty
    ask:  provide the user a chance to interact and pick what to do with
          commits which become empty on a case-by-case basis

In line with Junio's suggestion, if the --empty flag is not specified,
pick defaults as follows:
    explicitly interactive: ask
    otherwise: drop

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-02-16 15:40:42 -08:00

213 lines
6.6 KiB
C

#ifndef SEQUENCER_H
#define SEQUENCER_H
#include "cache.h"
#include "strbuf.h"
struct commit;
struct repository;
const char *git_path_commit_editmsg(void);
const char *git_path_seq_dir(void);
const char *rebase_path_todo(void);
const char *rebase_path_todo_backup(void);
#define APPEND_SIGNOFF_DEDUP (1u << 0)
enum replay_action {
REPLAY_REVERT,
REPLAY_PICK,
REPLAY_INTERACTIVE_REBASE
};
enum commit_msg_cleanup_mode {
COMMIT_MSG_CLEANUP_SPACE,
COMMIT_MSG_CLEANUP_NONE,
COMMIT_MSG_CLEANUP_SCISSORS,
COMMIT_MSG_CLEANUP_ALL
};
struct replay_opts {
enum replay_action action;
/* Boolean options */
int edit;
int record_origin;
int no_commit;
int signoff;
int allow_ff;
int allow_rerere_auto;
int allow_empty;
int allow_empty_message;
int drop_redundant_commits;
int keep_redundant_commits;
int verbose;
int quiet;
int reschedule_failed_exec;
int mainline;
char *gpg_sign;
enum commit_msg_cleanup_mode default_msg_cleanup;
int explicit_cleanup;
/* Merge strategy */
char *strategy;
char **xopts;
size_t xopts_nr, xopts_alloc;
/* Used by fixup/squash */
struct strbuf current_fixups;
int current_fixup_count;
/* placeholder commit for -i --root */
struct object_id squash_onto;
int have_squash_onto;
/* Only used by REPLAY_NONE */
struct rev_info *revs;
};
#define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
/*
* Note that ordering matters in this enum. Not only must it match the mapping
* of todo_command_info (in sequencer.c), it is also divided into several
* sections that matter. When adding new commands, make sure you add it in the
* right section.
*/
enum todo_command {
/* commands that handle commits */
TODO_PICK = 0,
TODO_REVERT,
TODO_EDIT,
TODO_REWORD,
TODO_FIXUP,
TODO_SQUASH,
/* commands that do something else than handling a single commit */
TODO_EXEC,
TODO_BREAK,
TODO_LABEL,
TODO_RESET,
TODO_MERGE,
/* commands that do nothing but are counted for reporting progress */
TODO_NOOP,
TODO_DROP,
/* comments (not counted for reporting progress) */
TODO_COMMENT
};
struct todo_item {
enum todo_command command;
struct commit *commit;
unsigned int flags;
int arg_len;
/* The offset of the command and its argument in the strbuf */
size_t offset_in_buf, arg_offset;
};
struct todo_list {
struct strbuf buf;
struct todo_item *items;
int nr, alloc, current;
int done_nr, total_nr;
struct stat_data stat;
};
#define TODO_LIST_INIT { STRBUF_INIT }
int todo_list_parse_insn_buffer(struct repository *r, char *buf,
struct todo_list *todo_list);
int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
const char *file, const char *shortrevisions,
const char *shortonto, int num, unsigned flags);
void todo_list_release(struct todo_list *todo_list);
const char *todo_item_get_arg(struct todo_list *todo_list,
struct todo_item *item);
/* Call this to setup defaults before parsing command line options */
void sequencer_init_config(struct replay_opts *opts);
int sequencer_pick_revisions(struct repository *repo,
struct replay_opts *opts);
int sequencer_continue(struct repository *repo, struct replay_opts *opts);
int sequencer_rollback(struct repository *repo, struct replay_opts *opts);
int sequencer_skip(struct repository *repo, struct replay_opts *opts);
int sequencer_remove_state(struct replay_opts *opts);
/* #define TODO_LIST_KEEP_EMPTY (1U << 0) */ /* No longer used */
#define TODO_LIST_SHORTEN_IDS (1U << 1)
#define TODO_LIST_ABBREVIATE_CMDS (1U << 2)
#define TODO_LIST_REBASE_MERGES (1U << 3)
/*
* When rebasing merges, commits that do have the base commit as ancestor
* ("cousins") are *not* rebased onto the new base by default. If those
* commits should be rebased onto the new base, this flag needs to be passed.
*/
#define TODO_LIST_REBASE_COUSINS (1U << 4)
#define TODO_LIST_APPEND_TODO_HELP (1U << 5)
/*
* When generating a script that rebases merges with `--root` *and* with
* `--onto`, we do not want to re-generate the root commits.
*/
#define TODO_LIST_ROOT_WITH_ONTO (1U << 6)
int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
const char **argv, unsigned flags);
void todo_list_add_exec_commands(struct todo_list *todo_list,
struct string_list *commands);
int check_todo_list_from_file(struct repository *r);
int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
const char *shortrevisions, const char *onto_name,
struct commit *onto, const char *orig_head, struct string_list *commands,
unsigned autosquash, struct todo_list *todo_list);
int todo_list_rearrange_squash(struct todo_list *todo_list);
/*
* Append a signoff to the commit message in "msgbuf". The ignore_footer
* parameter specifies the number of bytes at the end of msgbuf that should
* not be considered at all. I.e., they are not checked for existing trailers,
* and the new signoff will be spliced into the buffer before those bytes.
*/
void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
void append_conflicts_hint(struct index_state *istate,
struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
int use_editor);
void cleanup_message(struct strbuf *msgbuf,
enum commit_msg_cleanup_mode cleanup_mode, int verbose);
int message_is_empty(const struct strbuf *sb,
enum commit_msg_cleanup_mode cleanup_mode);
int template_untouched(const struct strbuf *sb, const char *template_file,
enum commit_msg_cleanup_mode cleanup_mode);
int update_head_with_reflog(const struct commit *old_head,
const struct object_id *new_head,
const char *action, const struct strbuf *msg,
struct strbuf *err);
void commit_post_rewrite(struct repository *r,
const struct commit *current_head,
const struct object_id *new_head);
int prepare_branch_to_be_rebased(struct repository *r, struct replay_opts *opts,
const char *commit);
#define SUMMARY_INITIAL_COMMIT (1 << 0)
#define SUMMARY_SHOW_AUTHOR_DATE (1 << 1)
void print_commit_summary(struct repository *repo,
const char *prefix,
const struct object_id *oid,
unsigned int flags);
int read_author_script(const char *path, char **name, char **email, char **date,
int allow_missing);
void parse_strategy_opts(struct replay_opts *opts, char *raw_opts);
int write_basic_state(struct replay_opts *opts, const char *head_name,
struct commit *onto, const char *orig_head);
void sequencer_post_commit_cleanup(struct repository *r, int verbose);
int sequencer_get_last_command(struct repository* r,
enum replay_action *action);
#endif /* SEQUENCER_H */