avoid error if two source files render the same destination file

There are two sub-caces. If both source files still exist, the winner that
renders the destination file is undefined. If one source file is deleted
and the other added, in a refresh, the new file will take over the
destination file.

2 files changed, 14 insertions, 2 deletions

diff --git a/IkiWiki.pm b/IkiWiki.pm
index 701f7137d..4acc5508a 100644
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -879,7 +879,19 @@ sub will_render ($$;$) {
 	# Important security check.
 	if (-e "$config{destdir}/$dest" && ! $config{rebuild} &&
 	    ! grep { $_ eq $dest } (@{$renderedfiles{$page}}, @{$oldrenderedfiles{$page}}, @{$wikistate{editpage}{previews}})) {
-		error("$config{destdir}/$dest independently created, not overwriting with version from $page");
+		my $from_other_page=0;
+		foreach my $p (keys %renderedfiles) {
+			if (grep {
+				$_ eq $dest ||
+				dirname($_) eq $dest
+			    } @{$renderedfiles{$p}}) {
+				$from_other_page=1;
+				last;
+			}
+		}
+
+		error("$config{destdir}/$dest independently created, not overwriting with version from $page")
+			unless $from_other_page;
 	}
 
 	if (! $clear || $cleared{$page}) {
diff --git a/t/conflicts.t b/t/conflicts.t
index ac270e806..81b2c12cb 100755
--- a/t/conflicts.t
+++ b/t/conflicts.t
@@ -2,7 +2,7 @@
 # Tests for bugs relating to conflicting files in the srcdir
 use warnings;
 use strict;
-use Test::More tests => 48;
+use Test::More tests => 76;
 
 # setup
 my $srcdir="t/tmp/src";