Merge branch 'js/advise-when-skipping-cherry-picked'

"git rebase" by default skips changes that are equivalent to
commits that are already in the history the branch is rebased onto;
give messages when this happens to let the users be aware of
skipped commits, and also teach them how to tell "rebase" to keep
duplicated changes.

* js/advise-when-skipping-cherry-picked:
  sequencer: advise if skipping cherry-picked commit

Documentation/config/advice.txt

@@ -44,6 +44,9 @@ advice.*::
 		Shown when linkgit:git-push[1] rejects a forced update of
 		a branch when its remote-tracking ref has updates that we
 		do not have locally.
+	skippedCherryPicks::
+		Shown when linkgit:git-rebase[1] skips a commit that has already
+		been cherry-picked onto the upstream branch.
 	statusAheadBehind::
 		Shown when linkgit:git-status[1] computes the ahead/behind
 		counts for a local ref compared to its remote tracking ref,

Documentation/git-rebase.txt

@@ -79,9 +79,10 @@ remain the checked-out branch.
 
 If the upstream branch already contains a change you have made (e.g.,
 because you mailed a patch which was applied upstream), then that commit
-will be skipped. For example, running `git rebase master` on the
-following history (in which `A'` and `A` introduce the same set of changes,
-but have different committer information):
+will be skipped and warnings will be issued (if the `merge` backend is
+used).  For example, running `git rebase master` on the following
+history (in which `A'` and `A` introduce the same set of changes, but
+have different committer information):
 
 ------------
           A---B---C topic
@@ -312,7 +313,10 @@ See also INCOMPATIBLE OPTIONS below.
 By default (or if `--no-reapply-cherry-picks` is given), these commits
 will be automatically dropped.  Because this necessitates reading all
 upstream commits, this can be expensive in repos with a large number
-of upstream commits that need to be read.
+of upstream commits that need to be read.  When using the `merge`
+backend, warnings will be issued for each dropped commit (unless
+`--quiet` is given). Advice will also be issued unless
+`advice.skippedCherryPicks` is set to false (see linkgit:git-config[1]).
 +
 `--reapply-cherry-picks` allows rebase to forgo reading all upstream
 commits, potentially improving performance.

advice.c

@@ -34,6 +34,7 @@ int advice_checkout_ambiguous_remote_branch_name = 1;
 int advice_submodule_alternate_error_strategy_die = 1;
 int advice_add_ignored_file = 1;
 int advice_add_empty_pathspec = 1;
+int advice_skipped_cherry_picks = 1;
 
 static int advice_use_color = -1;
 static char advice_colors[][COLOR_MAXLEN] = {
@@ -96,6 +97,7 @@ static struct {
 	{ "submoduleAlternateErrorStrategyDie", &advice_submodule_alternate_error_strategy_die },
 	{ "addIgnoredFile", &advice_add_ignored_file },
 	{ "addEmptyPathspec", &advice_add_empty_pathspec },
+	{ "skippedCherryPicks", &advice_skipped_cherry_picks },
 
 	/* make this an alias for backward compatibility */
 	{ "pushNonFastForward", &advice_push_update_rejected }
@@ -133,6 +135,7 @@ static struct {
 	[ADVICE_RM_HINTS]				= { "rmHints", 1 },
 	[ADVICE_SEQUENCER_IN_USE]			= { "sequencerInUse", 1 },
 	[ADVICE_SET_UPSTREAM_FAILURE]			= { "setUpstreamFailure", 1 },
+	[ADVICE_SKIPPED_CHERRY_PICKS]			= { "skippedCherryPicks", 1 },
 	[ADVICE_STATUS_AHEAD_BEHIND_WARNING]		= { "statusAheadBehindWarning", 1 },
 	[ADVICE_STATUS_HINTS]				= { "statusHints", 1 },
 	[ADVICE_STATUS_U_OPTION]			= { "statusUoption", 1 },

advice.h

@@ -35,6 +35,7 @@ extern int advice_checkout_ambiguous_remote_branch_name;
 extern int advice_submodule_alternate_error_strategy_die;
 extern int advice_add_ignored_file;
 extern int advice_add_empty_pathspec;
+extern int advice_skipped_cherry_picks;
 
 /*
  * To add a new advice, you need to:
@@ -75,6 +76,7 @@ extern int advice_add_empty_pathspec;
 	ADVICE_SUBMODULE_ALTERNATE_ERROR_STRATEGY_DIE,
 	ADVICE_UPDATE_SPARSE_PATH,
 	ADVICE_WAITING_FOR_EDITOR,
+	ADVICE_SKIPPED_CHERRY_PICKS,
 };
 
 int git_default_advice_config(const char *var, const char *value);

builtin/rebase.c

@@ -405,6 +405,7 @@ static int run_sequencer_rebase(struct rebase_options *opts,
 	flags |= opts->root_with_onto ? TODO_LIST_ROOT_WITH_ONTO : 0;
 	flags |= command == ACTION_SHORTEN_OIDS ? TODO_LIST_SHORTEN_IDS : 0;
 	flags |= opts->reapply_cherry_picks ? TODO_LIST_REAPPLY_CHERRY_PICKS : 0;
+	flags |= opts->flags & REBASE_NO_QUIET ? TODO_LIST_WARN_SKIPPED_CHERRY_PICKS : 0;
 
 	switch (command) {
 	case ACTION_NONE: {

sequencer.c

@@ -5110,6 +5110,7 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
 	int rebase_cousins = flags & TODO_LIST_REBASE_COUSINS;
 	int root_with_onto = flags & TODO_LIST_ROOT_WITH_ONTO;
+	int skipped_commit = 0;
 	struct strbuf buf = STRBUF_INIT, oneline = STRBUF_INIT;
 	struct strbuf label = STRBUF_INIT;
 	struct commit_list *commits = NULL, **tail = &commits, *iter;
@@ -5160,8 +5161,13 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		oidset_insert(&interesting, &commit->object.oid);
 
 		is_empty = is_original_commit_empty(commit);
-		if (!is_empty && (commit->object.flags & PATCHSAME))
+		if (!is_empty && (commit->object.flags & PATCHSAME)) {
+			if (flags & TODO_LIST_WARN_SKIPPED_CHERRY_PICKS)
+				warning(_("skipped previously applied commit %s"),
+					short_commit_name(commit));
+			skipped_commit = 1;
 			continue;
+		}
 		if (is_empty && !keep_empty)
 			continue;
 
@@ -5225,6 +5231,9 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		oidcpy(&entry->entry.oid, &commit->object.oid);
 		oidmap_put(&commit2todo, entry);
 	}
+	if (skipped_commit)
+		advise_if_enabled(ADVICE_SKIPPED_CHERRY_PICKS,
+				  _("use --reapply-cherry-picks to include skipped commits"));
 
 	/*
 	 * Second phase:
@@ -5345,6 +5354,7 @@ int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 	const char *insn = flags & TODO_LIST_ABBREVIATE_CMDS ? "p" : "pick";
 	int rebase_merges = flags & TODO_LIST_REBASE_MERGES;
 	int reapply_cherry_picks = flags & TODO_LIST_REAPPLY_CHERRY_PICKS;
+	int skipped_commit = 0;
 
 	repo_init_revisions(r, &revs, NULL);
 	revs.verbose_header = 1;
@@ -5380,8 +5390,13 @@ int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 	while ((commit = get_revision(&revs))) {
 		int is_empty = is_original_commit_empty(commit);
 
-		if (!is_empty && (commit->object.flags & PATCHSAME))
+		if (!is_empty && (commit->object.flags & PATCHSAME)) {
+			if (flags & TODO_LIST_WARN_SKIPPED_CHERRY_PICKS)
+				warning(_("skipped previously applied commit %s"),
+					short_commit_name(commit));
+			skipped_commit = 1;
 			continue;
+		}
 		if (is_empty && !keep_empty)
 			continue;
 		strbuf_addf(out, "%s %s ", insn,
@@ -5391,6 +5406,9 @@ int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 			strbuf_addf(out, " %c empty", comment_line_char);
 		strbuf_addch(out, '\n');
 	}
+	if (skipped_commit)
+		advise_if_enabled(ADVICE_SKIPPED_CHERRY_PICKS,
+				  _("use --reapply-cherry-picks to include skipped commits"));
 	return 0;
 }
 

sequencer.h

@@ -156,6 +156,7 @@ int sequencer_remove_state(struct replay_opts *opts);
  */
 #define TODO_LIST_ROOT_WITH_ONTO (1U << 6)
 #define TODO_LIST_REAPPLY_CHERRY_PICKS (1U << 7)
+#define TODO_LIST_WARN_SKIPPED_CHERRY_PICKS (1U << 8)
 
 int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 			  const char **argv, unsigned flags);