builtin-blame.c: allow more than 16 parents

This removes the hardcoded 16 parents limit from git-blame by allowing the
parent array to be allocated dynamically.  As the ultimate objective is
not about allowing dodecapus, but about annotating the history upside
down, it also renames "parent" in the code to "scapegoat"; the name of the
game used to be "pass blame to your parents", but now it is "find a
scapegoat to pass blame on".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-blame.c

@@ -1191,18 +1191,45 @@ static void pass_whole_blame(struct scoreboard *sb,
 	}
 }
 
-#define MAXPARENT 16
+/*
+ * We pass blame from the current commit to its parents.  We keep saying
+ * "parent" (and "porigin"), but what we mean is to find scapegoat to
+ * exonerate ourselves.
+ */
+static struct commit_list *first_scapegoat(struct commit *commit)
+{
+	return commit->parents;
+}
+
+static int num_scapegoats(struct commit *commit)
+{
+	int cnt;
+	struct commit_list *l = first_scapegoat(commit);
+	for (cnt = 0; l; l = l->next)
+		cnt++;
+	return cnt;
+}
+
+#define MAXSG 16
 
 static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 {
-	int i, pass;
+	int i, pass, num_sg;
 	struct commit *commit = origin->commit;
-	struct commit_list *parent;
-	struct origin *parent_origin[MAXPARENT], *porigin;
-
-	memset(parent_origin, 0, sizeof(parent_origin));
+	struct commit_list *sg;
+	struct origin *sg_buf[MAXSG];
+	struct origin *porigin, **sg_origin = sg_buf;
+
+	num_sg = num_scapegoats(commit);
+	if (!num_sg)
+		goto finish;
+	else if (num_sg < ARRAY_SIZE(sg_buf))
+		memset(sg_buf, 0, sizeof(sg_buf));
+	else
+		sg_origin = xcalloc(num_sg, sizeof(*sg_origin));
 
-	/* The first pass looks for unrenamed path to optimize for
+	/*
+	 * The first pass looks for unrenamed path to optimize for
 	 * common cases, then we look for renames in the second pass.
 	 */
 	for (pass = 0; pass < 2; pass++) {
@@ -1210,13 +1237,13 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 				       struct commit *, struct origin *);
 		find = pass ? find_rename : find_origin;
 
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct commit *p = parent->item;
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct commit *p = sg->item;
 			int j, same;
 
-			if (parent_origin[i])
+			if (sg_origin[i])
 				continue;
 			if (parse_commit(p))
 				continue;
@@ -1229,24 +1256,24 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 				goto finish;
 			}
 			for (j = same = 0; j < i; j++)
-				if (parent_origin[j] &&
-				    !hashcmp(parent_origin[j]->blob_sha1,
+				if (sg_origin[j] &&
+				    !hashcmp(sg_origin[j]->blob_sha1,
 					     porigin->blob_sha1)) {
 					same = 1;
 					break;
 				}
 			if (!same)
-				parent_origin[i] = porigin;
+				sg_origin[i] = porigin;
 			else
 				origin_decref(porigin);
 		}
 	}
 
 	num_commits++;
-	for (i = 0, parent = commit->parents;
-	     i < MAXPARENT && parent;
-	     parent = parent->next, i++) {
-		struct origin *porigin = parent_origin[i];
+	for (i = 0, sg = first_scapegoat(commit);
+	     i < num_sg && sg;
+	     sg = sg->next, i++) {
+		struct origin *porigin = sg_origin[i];
 		if (!porigin)
 			continue;
 		if (pass_blame_to_parent(sb, origin, porigin))
@@ -1257,10 +1284,10 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find moves in parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_MOVE)
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct origin *porigin = parent_origin[i];
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct origin *porigin = sg_origin[i];
 			if (!porigin)
 				continue;
 			if (find_move_in_parent(sb, origin, porigin))
@@ -1271,23 +1298,25 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find copies from parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_COPY)
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct origin *porigin = parent_origin[i];
-			if (find_copy_in_parent(sb, origin, parent->item,
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct origin *porigin = sg_origin[i];
+			if (find_copy_in_parent(sb, origin, sg->item,
 						porigin, opt))
 				goto finish;
 		}
 
  finish:
-	for (i = 0; i < MAXPARENT; i++) {
-		if (parent_origin[i]) {
-			drop_origin_blob(parent_origin[i]);
-			origin_decref(parent_origin[i]);
+	for (i = 0; i < num_sg; i++) {
+		if (sg_origin[i]) {
+			drop_origin_blob(sg_origin[i]);
+			origin_decref(sg_origin[i]);
 		}
 	}
 	drop_origin_blob(origin);
+	if (sg_buf != sg_origin)
+		free(sg_origin);
 }
 
 /*