Merge branch 'jc/rev-list-ancestry-path'

* jc/rev-list-ancestry-path:
  revision: Turn off history simplification in --ancestry-path mode
  revision: Fix typo in --ancestry-path error message
  Documentation/rev-list-options.txt: Explain --ancestry-path
  Documentation/rev-list-options.txt: Fix missing line in example history graph
  revision: --ancestry-path

revision.c

@@ -646,6 +646,93 @@ static int still_interesting(struct commit_list *src, unsigned long date, int sl
 	return slop-1;
 }
 
+/*
+ * "rev-list --ancestry-path A..B" computes commits that are ancestors
+ * of B but not ancestors of A but further limits the result to those
+ * that are descendants of A.  This takes the list of bottom commits and
+ * the result of "A..B" without --ancestry-path, and limits the latter
+ * further to the ones that can reach one of the commits in "bottom".
+ */
+static void limit_to_ancestry(struct commit_list *bottom, struct commit_list *list)
+{
+	struct commit_list *p;
+	struct commit_list *rlist = NULL;
+	int made_progress;
+
+	/*
+	 * Reverse the list so that it will be likely that we would
+	 * process parents before children.
+	 */
+	for (p = list; p; p = p->next)
+		commit_list_insert(p->item, &rlist);
+
+	for (p = bottom; p; p = p->next)
+		p->item->object.flags |= TMP_MARK;
+
+	/*
+	 * Mark the ones that can reach bottom commits in "list",
+	 * in a bottom-up fashion.
+	 */
+	do {
+		made_progress = 0;
+		for (p = rlist; p; p = p->next) {
+			struct commit *c = p->item;
+			struct commit_list *parents;
+			if (c->object.flags & (TMP_MARK | UNINTERESTING))
+				continue;
+			for (parents = c->parents;
+			     parents;
+			     parents = parents->next) {
+				if (!(parents->item->object.flags & TMP_MARK))
+					continue;
+				c->object.flags |= TMP_MARK;
+				made_progress = 1;
+				break;
+			}
+		}
+	} while (made_progress);
+
+	/*
+	 * NEEDSWORK: decide if we want to remove parents that are
+	 * not marked with TMP_MARK from commit->parents for commits
+	 * in the resulting list.  We may not want to do that, though.
+	 */
+
+	/*
+	 * The ones that are not marked with TMP_MARK are uninteresting
+	 */
+	for (p = list; p; p = p->next) {
+		struct commit *c = p->item;
+		if (c->object.flags & TMP_MARK)
+			continue;
+		c->object.flags |= UNINTERESTING;
+	}
+
+	/* We are done with the TMP_MARK */
+	for (p = list; p; p = p->next)
+		p->item->object.flags &= ~TMP_MARK;
+	for (p = bottom; p; p = p->next)
+		p->item->object.flags &= ~TMP_MARK;
+	free_commit_list(rlist);
+}
+
+/*
+ * Before walking the history, keep the set of "negative" refs the
+ * caller has asked to exclude.
+ *
+ * This is used to compute "rev-list --ancestry-path A..B", as we need
+ * to filter the result of "A..B" further to the ones that can actually
+ * reach A.
+ */
+static struct commit_list *collect_bottom_commits(struct commit_list *list)
+{
+	struct commit_list *elem, *bottom = NULL;
+	for (elem = list; elem; elem = elem->next)
+		if (elem->item->object.flags & UNINTERESTING)
+			commit_list_insert(elem->item, &bottom);
+	return bottom;
+}
+
 static int limit_list(struct rev_info *revs)
 {
 	int slop = SLOP;
@@ -653,6 +740,13 @@ static int limit_list(struct rev_info *revs)
 	struct commit_list *list = revs->commits;
 	struct commit_list *newlist = NULL;
 	struct commit_list **p = &newlist;
+	struct commit_list *bottom = NULL;
+
+	if (revs->ancestry_path) {
+		bottom = collect_bottom_commits(list);
+		if (!bottom)
+			die("--ancestry-path given but there are no bottom commits");
+	}
 
 	while (list) {
 		struct commit_list *entry = list;
@@ -694,6 +788,11 @@ static int limit_list(struct rev_info *revs)
 	if (revs->cherry_pick)
 		cherry_pick_list(newlist, revs);
 
+	if (bottom) {
+		limit_to_ancestry(bottom, newlist);
+		free_commit_list(bottom);
+	}
+
 	revs->commits = newlist;
 	return 0;
 }
@@ -1089,6 +1188,10 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->min_age = approxidate(arg + 8);
 	} else if (!strcmp(arg, "--first-parent")) {
 		revs->first_parent_only = 1;
+	} else if (!strcmp(arg, "--ancestry-path")) {
+		revs->ancestry_path = 1;
+		revs->simplify_history = 0;
+		revs->limited = 1;
 	} else if (!strcmp(arg, "-g") || !strcmp(arg, "--walk-reflogs")) {
 		init_reflog_walk(&revs->reflog_info);
 	} else if (!strcmp(arg, "--default")) {