revert: Save data for continuing after conflict resolution

Ever since v1.7.2-rc1~4^2~7 (revert: allow cherry-picking more than
one commit, 2010-06-02), a single invocation of "git cherry-pick" or
"git revert" can perform picks of several individual commits.  To
implement features like "--continue" to continue the whole operation,
we will need to store some information about the state and the plan at
the beginning.  Introduce a ".git/sequencer/head" file to store this
state, and ".git/sequencer/todo" file to store the plan.  The head
file contains the SHA-1 of the HEAD before the start of the operation,
and the todo file contains an instruction sheet whose format is
inspired by the format of the "rebase -i" instruction sheet.  As a
result, a typical todo file looks like:

  pick 8537f0e submodule add: test failure when url is not configured
  pick 4d68932 submodule add: allow relative repository path
  pick f22a17e submodule add: clean up duplicated code
  pick 59a5775 make copy_ref globally available

Since SHA-1 hex is abbreviated using an find_unique_abbrev(), it is
unambiguous.  This does not guarantee that there will be no ambiguity
when more objects are added to the repository.

These two files alone are not enough to implement a "--continue" that
remembers the command-line options specified; later patches in the
series save them too.

These new files are unrelated to the existing .git/CHERRY_PICK_HEAD,
which will still be useful while committing after a conflict
resolution.

Inspired-by: Christian Couder <chriscool@tuxfamily.org>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/revert.c b/builtin/revert.c
index f75c9cb6c83473bf9e499bbe71f06d4c0cc73110..54df8a23b8f0262974ef824fc72083f0c9da79ac 100644 (file)
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -13,6 +13,7 @@
 #include "rerere.h"
 #include "merge-recursive.h"
 #include "refs.h"
+#include "dir.h"
 
 /*
  * This implements the builtins revert and cherry-pick.
@@ -60,6 +61,10 @@ struct replay_opts {
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
+#define SEQ_DIR         "sequencer"
+#define SEQ_HEAD_FILE   "sequencer/head"
+#define SEQ_TODO_FILE   "sequencer/todo"
+
 static const char *action_name(const struct replay_opts *opts)
 {
        return opts->action == REVERT ? "revert" : "cherry-pick";
@@ -587,10 +592,116 @@ static void read_and_refresh_cache(struct replay_opts *opts)
        rollback_lock_file(&index_lock);
 }
 
-static int pick_commits(struct replay_opts *opts)
+/*
+ * Append a commit to the end of the commit_list.
+ *
+ * next starts by pointing to the variable that holds the head of an
+ * empty commit_list, and is updated to point to the "next" field of
+ * the last item on the list as new commits are appended.
+ *
+ * Usage example:
+ *
+ *     struct commit_list *list;
+ *     struct commit_list **next = &list;
+ *
+ *     next = commit_list_append(c1, next);
+ *     next = commit_list_append(c2, next);
+ *     assert(commit_list_count(list) == 2);
+ *     return list;
+ */
+struct commit_list **commit_list_append(struct commit *commit,
+                                       struct commit_list **next)
+{
+       struct commit_list *new = xmalloc(sizeof(struct commit_list));
+       new->item = commit;
+       *next = new;
+       new->next = NULL;
+       return &new->next;
+}
+
+static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
+               struct replay_opts *opts)
+{
+       struct commit_list *cur = NULL;
+       struct commit_message msg = { NULL, NULL, NULL, NULL, NULL };
+       const char *sha1_abbrev = NULL;
+       const char *action_str = opts->action == REVERT ? "revert" : "pick";
+
+       for (cur = todo_list; cur; cur = cur->next) {
+               sha1_abbrev = find_unique_abbrev(cur->item->object.sha1, DEFAULT_ABBREV);
+               if (get_message(cur->item, &msg))
+                       return error(_("Cannot get commit message for %s"), sha1_abbrev);
+               strbuf_addf(buf, "%s %s %s\n", action_str, sha1_abbrev, msg.subject);
+       }
+       return 0;
+}
+
+static void walk_revs_populate_todo(struct commit_list **todo_list,
+                               struct replay_opts *opts)
 {
        struct rev_info revs;
        struct commit *commit;
+       struct commit_list **next;
+
+       prepare_revs(&revs, opts);
+
+       next = todo_list;
+       while ((commit = get_revision(&revs)))
+               next = commit_list_append(commit, next);
+}
+
+static void create_seq_dir(void)
+{
+       const char *seq_dir = git_path(SEQ_DIR);
+
+       if (!(file_exists(seq_dir) && is_directory(seq_dir))
+               && mkdir(seq_dir, 0777) < 0)
+               die_errno(_("Could not create sequencer directory '%s'."), seq_dir);
+}
+
+static void save_head(const char *head)
+{
+       const char *head_file = git_path(SEQ_HEAD_FILE);
+       static struct lock_file head_lock;
+       struct strbuf buf = STRBUF_INIT;
+       int fd;
+
+       fd = hold_lock_file_for_update(&head_lock, head_file, LOCK_DIE_ON_ERROR);
+       strbuf_addf(&buf, "%s\n", head);
+       if (write_in_full(fd, buf.buf, buf.len) < 0)
+               die_errno(_("Could not write to %s."), head_file);
+       if (commit_lock_file(&head_lock) < 0)
+               die(_("Error wrapping up %s."), head_file);
+}
+
+static void save_todo(struct commit_list *todo_list, struct replay_opts *opts)
+{
+       const char *todo_file = git_path(SEQ_TODO_FILE);
+       static struct lock_file todo_lock;
+       struct strbuf buf = STRBUF_INIT;
+       int fd;
+
+       fd = hold_lock_file_for_update(&todo_lock, todo_file, LOCK_DIE_ON_ERROR);
+       if (format_todo(&buf, todo_list, opts) < 0)
+               die(_("Could not format %s."), todo_file);
+       if (write_in_full(fd, buf.buf, buf.len) < 0) {
+               strbuf_release(&buf);
+               die_errno(_("Could not write to %s."), todo_file);
+       }
+       if (commit_lock_file(&todo_lock) < 0) {
+               strbuf_release(&buf);
+               die(_("Error wrapping up %s."), todo_file);
+       }
+       strbuf_release(&buf);
+}
+
+static int pick_commits(struct replay_opts *opts)
+{
+       struct commit_list *todo_list = NULL;
+       struct strbuf buf = STRBUF_INIT;
+       unsigned char sha1[20];
+       struct commit_list *cur;
+       int res;
 
        setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
        if (opts->allow_ff)
@@ -598,14 +709,29 @@ static int pick_commits(struct replay_opts *opts)
                                opts->record_origin || opts->edit));
        read_and_refresh_cache(opts);
 
-       prepare_revs(&revs, opts);
+       walk_revs_populate_todo(&todo_list, opts);
+       create_seq_dir();
+       if (get_sha1("HEAD", sha1)) {
+               if (opts->action == REVERT)
+                       die(_("Can't revert as initial commit"));
+               die(_("Can't cherry-pick into empty head"));
+       }
+       save_head(sha1_to_hex(sha1));
 
-       while ((commit = get_revision(&revs))) {
-               int res = do_pick_commit(commit, opts);
+       for (cur = todo_list; cur; cur = cur->next) {
+               save_todo(cur, opts);
+               res = do_pick_commit(cur->item, opts);
                if (res)
                        return res;
        }
 
+       /*
+        * Sequence of picks finished successfully; cleanup by
+        * removing the .git/sequencer directory
+        */
+       strbuf_addf(&buf, "%s", git_path(SEQ_DIR));
+       remove_dir_recursively(&buf, 0);
+       strbuf_release(&buf);
        return 0;
 }
 

diff --git a/t/t3510-cherry-pick-sequence.sh b/t/t3510-cherry-pick-sequence.sh
new file mode 100755 (executable)
index 0000000..a2c70ad
--- /dev/null
+++ b/t/t3510-cherry-pick-sequence.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+
+test_description='Test cherry-pick continuation features
+
+  + anotherpick: rewrites foo to d
+  + picked: rewrites foo to c
+  + unrelatedpick: rewrites unrelated to reallyunrelated
+  + base: rewrites foo to b
+  + initial: writes foo as a, unrelated as unrelated
+
+'
+
+. ./test-lib.sh
+
+pristine_detach () {
+       rm -rf .git/sequencer &&
+       git checkout -f "$1^0" &&
+       git read-tree -u --reset HEAD &&
+       git clean -d -f -f -q -x
+}
+
+test_expect_success setup '
+       echo unrelated >unrelated &&
+       git add unrelated &&
+       test_commit initial foo a &&
+       test_commit base foo b &&
+       test_commit unrelatedpick unrelated reallyunrelated &&
+       test_commit picked foo c &&
+       test_commit anotherpick foo d &&
+       git config advice.detachedhead false
+
+'
+
+test_expect_success 'cherry-pick persists data on failure' '
+       pristine_detach initial &&
+       test_must_fail git cherry-pick base..anotherpick &&
+       test_path_is_dir .git/sequencer &&
+       test_path_is_file .git/sequencer/head &&
+       test_path_is_file .git/sequencer/todo
+'
+
+test_expect_success 'cherry-pick cleans up sequencer state upon success' '
+       pristine_detach initial &&
+       git cherry-pick initial..picked &&
+       test_path_is_missing .git/sequencer
+'
+
+test_done