Merge branch 'jc/rev-list-simplify-merges-first-parent'

When "--simplify-merges/by-decoration" is given together with
"--first-parent" to "git log", the combination of these options
makes the simplification logic to use in-core commit objects that
haven't been examined for relevance, either producing incorrect
result or taking too long to produce any output.  Teach the
simplification logic to ignore commits that the first-parent
traversal logic ignored when both are in effect to work around the
issue.

revision.c

@@ -1358,11 +1358,13 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->topo_order = 1;
 	} else if (!strcmp(arg, "--simplify-merges")) {
 		revs->simplify_merges = 1;
+		revs->topo_order = 1;
 		revs->rewrite_parents = 1;
 		revs->simplify_history = 0;
 		revs->limited = 1;
 	} else if (!strcmp(arg, "--simplify-by-decoration")) {
 		revs->simplify_merges = 1;
+		revs->topo_order = 1;
 		revs->rewrite_parents = 1;
 		revs->simplify_history = 0;
 		revs->simplify_by_decoration = 1;
@@ -1947,15 +1949,18 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 	}
 
 	/*
-	 * Do we know what commit all of our parents should be rewritten to?
-	 * Otherwise we are not ready to rewrite this one yet.
+	 * Do we know what commit all of our parents that matter
+	 * should be rewritten to?  Otherwise we are not ready to
+	 * rewrite this one yet.
 	 */
 	for (cnt = 0, p = commit->parents; p; p = p->next) {
 		pst = locate_simplify_state(revs, p->item);
 		if (!pst->simplified) {
 			tail = &commit_list_insert(p->item, tail)->next;
 			cnt++;
 		}
+		if (revs->first_parent_only)
+			break;
 	}
 	if (cnt) {
 		tail = &commit_list_insert(commit, tail)->next;
@@ -1968,8 +1973,13 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 	for (p = commit->parents; p; p = p->next) {
 		pst = locate_simplify_state(revs, p->item);
 		p->item = pst->simplified;
+		if (revs->first_parent_only)
+			break;
 	}
-	cnt = remove_duplicate_parents(commit);
+	if (!revs->first_parent_only)
+		cnt = remove_duplicate_parents(commit);
+	else
+		cnt = 1;
 
 	/*
 	 * It is possible that we are a merge and one side branch
@@ -2013,25 +2023,31 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 
 static void simplify_merges(struct rev_info *revs)
 {
-	struct commit_list *list;
+	struct commit_list *list, *next;
 	struct commit_list *yet_to_do, **tail;
+	struct commit *commit;
 
-	if (!revs->topo_order)
-		sort_in_topological_order(&revs->commits, revs->lifo);
 	if (!revs->prune)
 		return;
 
 	/* feed the list reversed */
 	yet_to_do = NULL;
-	for (list = revs->commits; list; list = list->next)
-		commit_list_insert(list->item, &yet_to_do);
+	for (list = revs->commits; list; list = next) {
+		commit = list->item;
+		next = list->next;
+		/*
+		 * Do not free(list) here yet; the original list
+		 * is used later in this function.
+		 */
+		commit_list_insert(commit, &yet_to_do);
+	}
 	while (yet_to_do) {
 		list = yet_to_do;
 		yet_to_do = NULL;
 		tail = &yet_to_do;
 		while (list) {
-			struct commit *commit = list->item;
-			struct commit_list *next = list->next;
+			commit = list->item;
+			next = list->next;
 			free(list);
 			list = next;
 			tail = simplify_one(revs, commit, tail);
@@ -2043,9 +2059,10 @@ static void simplify_merges(struct rev_info *revs)
 	revs->commits = NULL;
 	tail = &revs->commits;
 	while (list) {
-		struct commit *commit = list->item;
-		struct commit_list *next = list->next;
 		struct merge_simplify_state *st;
+
+		commit = list->item;
+		next = list->next;
 		free(list);
 		list = next;
 		st = locate_simplify_state(revs, commit);