log: fix --max-count when used together with -S or -G

The --max-count limit is implemented by counting revisions in
get_revision(), but the -S and -G take effect later when running diff.
Hence "--max-count=10 -Sfoo" meant "examine the 10 first revisions, and
out of them, show only those changing the occurences of foo", not "show 10
revisions changing the occurences of foo".

In case the commit isn't actually shown, cancel the decrement of
max_count.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -263,7 +263,13 @@ static int cmd_log_walk(struct rev_info *rev)
 	 * retain that state information if replacing rev->diffopt in this loop
 	 */
 	while ((commit = get_revision(rev)) != NULL) {
-		log_tree_commit(rev, commit);
+		if (!log_tree_commit(rev, commit) &&
+		    rev->max_count >= 0)
+			/*
+			 * We decremented max_count in get_revision,
+			 * but we didn't actually show the commit.
+			 */
+			rev->max_count++;
 		if (!rev->reflog_info) {
 			/* we allow cycles in reflog ancestry */
 			free(commit->buffer);

t/t4013-diff-various.sh

@@ -210,6 +210,9 @@ log -m -p master
 log -SF master
 log -S F master
 log -SF -p master
+log -SF master --max-count=0
+log -SF master --max-count=1
+log -SF master --max-count=2
 log -GF master
 log -GF -p master
 log -GF -p --pickaxe-all master

t/t4013/diff.log_-SF_master_--max-count=0

@@ -0,0 +1,2 @@
+$ git log -SF master --max-count=0
+$

t/t4013/diff.log_-SF_master_--max-count=1

@@ -0,0 +1,7 @@
+$ git log -SF master --max-count=1
+commit 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:02:00 2006 +0000
+
+    Third
+$

t/t4013/diff.log_-SF_master_--max-count=2

@@ -0,0 +1,7 @@
+$ git log -SF master --max-count=2
+commit 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:02:00 2006 +0000
+
+    Third
+$