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>

7 files changed, 21 insertions, 25 deletions

diff --git a/Debian/Debhelper/Buildsystem/ant.pm b/Debian/Debhelper/Buildsystem/ant.pm
index 26bee95b..938fb446 100644
--- a/Debian/Debhelper/Buildsystem/ant.pm
+++ b/Debian/Debhelper/Buildsystem/ant.pm
@@ -14,7 +14,7 @@ sub DESCRIPTION {
 
 sub check_auto_buildable {
 	my $this=shift;
-	return -e $this->get_sourcepath("build.xml");
+	return $this->get_sourcepath("build.xml") ? 1 : 0;
 }
 
 sub new {
diff --git a/Debian/Debhelper/Buildsystem/autoconf.pm b/Debian/Debhelper/Buildsystem/autoconf.pm
index a97de9c6..d7b0bed2 100644
--- a/Debian/Debhelper/Buildsystem/autoconf.pm
+++ b/Debian/Debhelper/Buildsystem/autoconf.pm
@@ -18,9 +18,9 @@ sub check_auto_buildable {
 	my $this=shift;
 	my ($step)=@_;
 
-	# Handle configure; the rest - next class
+	# Handle configure; the rest - next class (compat with 7.0.x code path)
 	if ($step eq "configure") {
-		return -x $this->get_sourcepath("configure");
+		return 1 if -x $this->get_sourcepath("configure");
 	}
 	return 0;
 }
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 {
diff --git a/Debian/Debhelper/Buildsystem/makefile.pm b/Debian/Debhelper/Buildsystem/makefile.pm
index 704f9c95..083abc42 100644
--- a/Debian/Debhelper/Buildsystem/makefile.pm
+++ b/Debian/Debhelper/Buildsystem/makefile.pm
@@ -71,15 +71,11 @@ sub check_auto_buildable {
 	my $this=shift;
 	my ($step) = @_;
 
-	# Handles build, test, install, clean; configure - next class
-	if (grep /^\Q$step\E$/, qw{build test install clean}) {
-		# This is always called in the source directory, but generally
-		# Makefiles are created (or live) in the the build directory.
-		return -e $this->get_buildpath("Makefile") ||
-		       -e $this->get_buildpath("makefile") ||
-		       -e $this->get_buildpath("GNUmakefile");
-	}
-	return 0;
+	# This is always called in the source directory, but generally
+	# Makefiles are created (or live) in the the build directory.
+	return (-e $this->get_buildpath("Makefile") ||
+	        -e $this->get_buildpath("makefile") ||
+	        -e $this->get_buildpath("GNUmakefile")) ? 1 : 0;
 }
 
 sub build {
diff --git a/Debian/Debhelper/Buildsystem/perl_build.pm b/Debian/Debhelper/Buildsystem/perl_build.pm
index 8974be2e..2afa5e59 100644
--- a/Debian/Debhelper/Buildsystem/perl_build.pm
+++ b/Debian/Debhelper/Buildsystem/perl_build.pm
@@ -21,7 +21,7 @@ sub check_auto_buildable {
 	if ($step ne "configure") {
 		$ret &&= -e $this->get_sourcepath("Build");
 	}
-	return $ret;
+	return $ret ? 1 : 0;
 }
 
 sub do_perl {
diff --git a/Debian/Debhelper/Buildsystem/perl_makemaker.pm b/Debian/Debhelper/Buildsystem/perl_makemaker.pm
index e109be57..473a3a7e 100644
--- a/Debian/Debhelper/Buildsystem/perl_makemaker.pm
+++ b/Debian/Debhelper/Buildsystem/perl_makemaker.pm
@@ -19,7 +19,7 @@ sub check_auto_buildable {
 
 	# Handles everything if Makefile.PL exists. Otherwise - next class.
 	if (-e $this->get_sourcepath("Makefile.PL")) {
-		if ($step eq "install" || $step eq "configure") {
+		if ($step eq "configure") {
 			return 1;
 		}
 		else {
diff --git a/Debian/Debhelper/Buildsystem/python_distutils.pm b/Debian/Debhelper/Buildsystem/python_distutils.pm
index 219c6f9b..70307b0f 100644
--- a/Debian/Debhelper/Buildsystem/python_distutils.pm
+++ b/Debian/Debhelper/Buildsystem/python_distutils.pm
@@ -31,7 +31,7 @@ sub new {
 
 sub check_auto_buildable {
 	my $this=shift;
-	return -e $this->get_sourcepath("setup.py");
+	return -e $this->get_sourcepath("setup.py") ? 1 : 0;
 }
 
 sub not_our_cfg {
@@ -117,10 +117,10 @@ sub setup_py {
 	# Then, run setup.py with each available python, to build
 	# extensions for each.
 
-        my $python_default = `pyversions -d`;
-        $python_default =~ s/^\s+//;
-        $python_default =~ s/\s+$//;
-        my @python_requested = split ' ', `pyversions -r 2>/dev/null`;
+	my $python_default = `pyversions -d`;
+	$python_default =~ s/^\s+//;
+	$python_default =~ s/\s+$//;
+	my @python_requested = split ' ', `pyversions -r 2>/dev/null`;
 	if (grep /^\Q$python_default\E/, @python_requested) {
 		@python_requested = (
 			grep(!/^\Q$python_default\E/, @python_requested),
@@ -129,7 +129,7 @@ sub setup_py {
 	}
 
 	my @python_dbg;
-        my @dbg_build_needed = $this->dbg_build_needed();
+	my @dbg_build_needed = $this->dbg_build_needed();
 	foreach my $python (map { $_."-dbg" } @python_requested) {
 		if (grep /^(python-all-dbg|\Q$python\E)/, @dbg_build_needed) {
 			push @python_dbg, $python;