Add substitution for finding package share directory (#57)

* Add substitution for finding package share directory

Expose FindPackageShare as 'find-pkg-share' and FindPackagePrefix as 'find-pkg-prefix'.

This turns

    <include file="$(find-pkg foo)/share/foo/launch/foo.launch.xml">

into

    <include file="$(find-pkg-share foo)/launch/foo.launch.xml">

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Refactor to use abstract class

FindPackage is now an abstract class that requires subclasses to implement a 'find' method.
FindPackagePrefix is the subclass that finds the package prefix.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

* Update error message and describe() method

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

launch_ros/launch_ros/substitutions/__init__.py

@@ -16,9 +16,13 @@
 
 from .executable_in_package import ExecutableInPackage
 from .find_package import FindPackage
+from .find_package import FindPackagePrefix
+from .find_package import FindPackageShare
 
 
 __all__ = [
     'ExecutableInPackage',
     'FindPackage',
+    'FindPackagePrefix',
+    'FindPackageShare',
 ]

launch_ros/launch_ros/substitutions/executable_in_package.py

@@ -29,11 +29,11 @@
 
 from osrf_pycommon.process_utils import which
 
-from .find_package import FindPackage
+from .find_package import FindPackagePrefix
 
 
 @expose_substitution('exec-in-pkg')
-class ExecutableInPackage(FindPackage):
+class ExecutableInPackage(FindPackagePrefix):
     """
     Substitution that tries to locate an executable in the libexec directory of a ROS package.
 

launch_ros/launch_ros/substitutions/find_package.py

@@ -19,6 +19,7 @@
 from typing import Text
 
 from ament_index_python.packages import get_package_prefix
+from ament_index_python.packages import get_package_share_directory
 
 from launch.frontend import expose_substitution
 from launch.launch_context import LaunchContext
@@ -28,18 +29,17 @@
 from launch.utilities import perform_substitutions
 
 
-@expose_substitution('find-pkg')
 class FindPackage(Substitution):
     """
-    Substitution that tries to locate the package prefix of a ROS package.
-
-    The ROS package is located using ament_index_python.
+    Abstract base class for substitutions involving finding a package.
 
-    :raise: ament_index_python.packages.PackageNotFoundError when package is
-        not found during substitution.
+    Subclasses should implement the find() method.
     """
 
-    def __init__(self, package: SomeSubstitutionsType) -> None:
+    def __init__(
+        self,
+        package: SomeSubstitutionsType,
+    ) -> None:
         """Constructor."""
         super().__init__()
         self.__package = normalize_to_list_of_substitutions(package)
@@ -48,7 +48,7 @@ def __init__(self, package: SomeSubstitutionsType) -> None:
     def parse(cls, data: Iterable[SomeSubstitutionsType]):
         """Parse a FindPackage substitution."""
         if not data or len(data) != 1:
-            raise AttributeError('find-package substitution expects 1 argument')
+            raise AttributeError('find package substitutions expect 1 argument')
         kwargs = {'package': data[0]}
         return cls, kwargs
 
@@ -57,13 +57,56 @@ def package(self) -> List[Substitution]:
         """Getter for package."""
         return self.__package
 
+    def find(self, package_name: Text) -> Text:
+        """
+        Find a directory for a package.
+
+        Called when the substitution is performed.
+
+        :param: package_name The name of the package.
+        :return: A directory related to the package.
+        """
+        raise NotImplementedError()
+
     def describe(self) -> Text:
         """Return a description of this substitution as a string."""
         pkg_str = ' + '.join([sub.describe() for sub in self.package])
-        return 'Pkg(pkg={})'.format(pkg_str)
+        return '{}(pkg={})'.format(self.__class__.__name__, pkg_str)
 
     def perform(self, context: LaunchContext) -> Text:
         """Perform the substitution by locating the package."""
         package = perform_substitutions(context, self.package)
-        result = get_package_prefix(package)
+        result = self.find(package)
         return result
+
+
+@expose_substitution('find-pkg-prefix')
+class FindPackagePrefix(FindPackage):
+    """
+    Substitution that tries to locate the package prefix of a ROS package.
+
+    The ROS package is located using ament_index_python.
+
+    :raise: ament_index_python.packages.PackageNotFoundError when package is
+        not found during substitution.
+    """
+
+    def find(self, package_name: Text) -> Text:
+        """Find the package prefix."""
+        return get_package_prefix(package_name)
+
+
+@expose_substitution('find-pkg-share')
+class FindPackageShare(FindPackage):
+    """
+    Substitution that tries to locate the share directory of a ROS package.
+
+    The directory is located using ament_index_python.
+
+    :raise: ament_index_python.packages.PackageNotFoundError when package is
+        not found during substitution.
+    """
+
+    def find(self, package_name: Text) -> Text:
+        """Find the share directory of a package."""
+        return get_package_share_directory(package_name)

test_launch_ros/test/test_launch_ros/substitutions/test_find_package.py

@@ -12,18 +12,27 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Test for the FindPackage substitution."""
+"""Test for the FindPackage substitutions."""
 
 from pathlib import Path
 
 from launch import LaunchContext
 
-from launch_ros.substitutions import FindPackage
+from launch_ros.substitutions import FindPackagePrefix
+from launch_ros.substitutions import FindPackageShare
 
 
-def test_find_package():
-    sub = FindPackage('launch_ros')
+def test_find_package_prefix():
+    sub = FindPackagePrefix('launch_ros')
     context = LaunchContext()
     package_prefix = Path(sub.perform(context))
     package_xml_file = package_prefix / Path('share/launch_ros/package.xml')
     assert package_xml_file.is_file()
+
+
+def test_find_package_share():
+    sub = FindPackageShare('launch_ros')
+    context = LaunchContext()
+    package_prefix = Path(sub.perform(context))
+    package_xml_file = package_prefix / Path('package.xml')
+    assert package_xml_file.is_file()