Extend package discovery to support passive mechanisms

colcon_core/package_discovery/__init__.py

@@ -25,14 +25,14 @@ class PackageDiscoveryExtensionPoint:
     """
 
     """The version of the discovery extension interface."""
-    EXTENSION_POINT_VERSION = '1.0'
+    EXTENSION_POINT_VERSION = '1.1'
 
     """The default priority of discovery extensions."""
     PRIORITY = 100
 
     def has_default(self):
         """
-        Check if the extension has a default parameter is none are provided.
+        Check if the extension has a default parameter if none are provided.
 
         The method is intended to be overridden in a subclass.
 
@@ -62,7 +62,9 @@ def has_parameters(self, *, args):
         This method must be overridden in a subclass.
 
         :param args: The parsed command line arguments
-        :returns: True if `discover()` should be called, False otherwise
+        :returns: True if `discover()` should be called, False if no
+          parameters were given, or None if this extension has no
+          parameters to be specified.
         :rtype: bool
         """
         raise NotImplementedError()
@@ -219,6 +221,7 @@ def expand_dir_wildcards(paths):
 def _get_extensions_with_parameters(
     args, discovery_extensions
 ):
+    explicitly_specified = False
     with_parameters = OrderedDict()
     for extension in discovery_extensions.values():
         logger.log(
@@ -235,8 +238,11 @@ def _get_extensions_with_parameters(
             # skip failing extension, continue with next one
         else:
             if has_parameter:
-                with_parameters[extension.PACKAGE_DISCOVERY_NAME] = extension
-    return with_parameters
+                explicitly_specified = True
+            elif has_parameter is not None:
+                continue
+            with_parameters[extension.PACKAGE_DISCOVERY_NAME] = extension
+    return with_parameters if explicitly_specified else OrderedDict()
 
 
 def _discover_packages(

test/test_package_discovery.py

@@ -110,6 +110,7 @@ def test_discover_packages():
             return_value={PackageDescriptor('/extension1/pkg1')})
         extensions['extension2'].discover = Mock(
             return_value={PackageDescriptor('/extension2/pkg1')})
+        extensions['extension2'].has_parameters = Mock(return_value=None)
 
         descs = discover_packages(None, None, discovery_extensions=extensions)
         assert len(descs) == 2
@@ -126,11 +127,13 @@ def test_discover_packages():
                 PackageDescriptor('/extension3/pkg2')})
 
         descs = discover_packages(None, None, discovery_extensions=extensions)
-        assert len(descs) == 2
+        assert len(descs) == 3
         expected_path = '/extension3/pkg1'.replace('/', os.sep)
         assert expected_path in (str(d.path) for d in descs)
         expected_path = '/extension3/pkg2'.replace('/', os.sep)
         assert expected_path in (str(d.path) for d in descs)
+        expected_path = '/extension2/pkg1'.replace('/', os.sep)
+        assert expected_path in (str(d.path) for d in descs)
 
 
 def test_expand_dir_wildcards():