name-rev: Fix non-shortest description

Uwe Kleine-König noticed that under certain circumstances, name-rev
picked a non-optimal tag.  Jeff King analyzed that name-rev only
takes into account the number of merge traversals, and then the
_last_ number in the description.

As an easy way to fix it, use a weighting factor for merge traversals:
A merge traversal is now made 65535 times more expensive than a
first-parent traversal.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Acked-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-name-rev.c

@@ -11,14 +11,17 @@ static const char name_rev_usage[] =
 
 typedef struct rev_name {
 	const char *tip_name;
-	int merge_traversals;
 	int generation;
+	int distance;
 } rev_name;
 
 static long cutoff = LONG_MAX;
 
+/* How many generations are maximally preferred over _one_ merge traversal? */
+#define MERGE_TRAVERSAL_WEIGHT 65535
+
 static void name_rev(struct commit *commit,
-		const char *tip_name, int merge_traversals, int generation,
+		const char *tip_name, int generation, int distance,
 		int deref)
 {
 	struct rev_name *name = (struct rev_name *)commit->util;
@@ -45,13 +48,11 @@ static void name_rev(struct commit *commit,
 		name = xmalloc(sizeof(rev_name));
 		commit->util = name;
 		goto copy_data;
-	} else if (name->merge_traversals > merge_traversals ||
-			(name->merge_traversals == merge_traversals &&
-			 name->generation > generation)) {
+	} else if (name->distance > distance) {
 copy_data:
 		name->tip_name = tip_name;
-		name->merge_traversals = merge_traversals;
 		name->generation = generation;
+		name->distance = distance;
 	} else
 		return;
 
@@ -74,11 +75,11 @@ static void name_rev(struct commit *commit,
 				sprintf(new_name, "%.*s^%d", len, tip_name,
 						parent_number);
 
-			name_rev(parents->item, new_name,
-				merge_traversals + 1 , 0, 0);
+			name_rev(parents->item, new_name, 0,
+				distance + MERGE_TRAVERSAL_WEIGHT, 0);
 		} else {
-			name_rev(parents->item, tip_name, merge_traversals,
-				generation + 1, 0);
+			name_rev(parents->item, tip_name, generation + 1,
+				distance + 1, 0);
 		}
 	}
 }