Improve build system auto-selection process

This patch alters semantics of check_auto_buildable() a bit. Now it can
also indicate if the source has already been partitially built with the
build system and if so, such build system may be auto-selected over a less
specific its parent (in the inheritance tree) even if the latter is earlier
in the @BUILDSYSTEMS array.

However, this still leaves a requirement that a derivative build system
must not do anything that may break packages of the parent build system.
Otherwise, introduction of a new derivative build system might break
packages which already had that build system implemented via overrides...

Signed-off-by: Modestas Vainius <modestas@vainius.eu>

1 files changed, 5 insertions, 5 deletions

diff --git a/Debian/Debhelper/Buildsystem/cmake.pm b/Debian/Debhelper/Buildsystem/cmake.pm
index 03e6ade5..3eddc74f 100644
--- a/Debian/Debhelper/Buildsystem/cmake.pm
+++ b/Debian/Debhelper/Buildsystem/cmake.pm
@@ -16,12 +16,12 @@ sub DESCRIPTION {
 sub check_auto_buildable {
 	my $this=shift;
 	my ($step)=@_;
-	my $ret = -e $this->get_sourcepath("CMakeLists.txt");
-	if ($step ne "configure") {
-		$ret &&= -e $this->get_buildpath("CMakeCache.txt") &&
-		         $this->SUPER::check_auto_buildable(@_);
+	if (-e $this->get_sourcepath("CMakeLists.txt")) {
+		my $ret = $this->SUPER::check_auto_buildable(@_);
+		$ret++ if ($ret && -e $this->get_buildpath("CMakeCache.txt"));
+		return $ret > 0 ? $ret : 1;
 	}
-	return $ret;
+	return 0;
 }
 
 sub new {