Refactor launch.frontend file loading (ros2#271)

Signed-off-by: ivanpauno <[email protected]>

launch/launch/__init__.py

@@ -24,6 +24,7 @@
 from .condition import Condition
 from .event import Event
 from .event_handler import EventHandler
+from .invalid_launch_file_error import InvalidLaunchFileError
 from .launch_context import LaunchContext
 from .launch_description import LaunchDescription
 from .launch_description_entity import LaunchDescriptionEntity
@@ -47,6 +48,7 @@
     'Condition',
     'Event',
     'EventHandler',
+    'InvalidLaunchFileError',
     'LaunchContext',
     'LaunchDescription',
     'LaunchDescriptionEntity',

launch/launch/frontend/__init__.py

@@ -17,11 +17,12 @@
 from . import type_utils
 from .entity import Entity
 from .expose import expose_action, expose_substitution
-from .parser import Parser
+from .parser import InvalidFrontendLaunchFileError, Parser
 
 
 __all__ = [
     'Entity',
+    'InvalidFrontendLaunchFileError',
     'Parser',
     'expose_action',
     'expose_substitution',

launch/launch/frontend/parser.py

@@ -15,9 +15,13 @@
 """Module for Parser class and parsing methods."""
 
 import io
+import os
 from typing import Any
+from typing import List
+from typing import Optional
 from typing import Text
 from typing import Tuple
+from typing import Type
 from typing import Union
 
 from pkg_resources import iter_entry_points
@@ -27,6 +31,7 @@
 from .parse_substitution import parse_substitution
 from .parse_substitution import replace_escaped_characters
 from ..action import Action
+from ..invalid_launch_file_error import InvalidLaunchFileError
 from ..some_substitutions_type import SomeSubstitutionsType
 from ..utilities import is_a
 
@@ -39,6 +44,12 @@
     from ..launch_description import LaunchDescription  # noqa: F401
 
 
+class InvalidFrontendLaunchFileError(InvalidLaunchFileError):
+    """Exception raised when the given frontend launch file is not valid."""
+
+    ...
+
+
 class Parser:
     """
     Abstract class for parsing launch actions, substitutions and descriptions.
@@ -90,28 +101,71 @@ def parse_description(self, entity: Entity) -> 'LaunchDescription':
         actions = [self.parse_action(child) for child in entity.children]
         return LaunchDescription(actions)
 
+    @classmethod
+    def get_available_extensions(cls) -> List[Text]:
+        """Return the registered extensions."""
+        cls.load_parser_implementations()
+        return cls.frontend_parsers.keys()
+
+    @classmethod
+    def is_extension_valid(
+        cls,
+        extension: Text,
+    ) -> bool:
+        """Return an entity loaded with a markup file."""
+        cls.load_parser_implementations()
+        return extension in cls.frontend_parsers
+
+    @classmethod
+    def get_parser_from_extension(
+        cls,
+        extension: Text,
+    ) -> Optional[Type['Parser']]:
+        """Return an entity loaded with a markup file."""
+        cls.load_parser_implementations()
+        try:
+            return cls.frontend_parsers[extension]
+        except KeyError:
+            raise RuntimeError('Not recognized frontend implementation')
+
     @classmethod
     def load(
         cls,
         file: Union[str, io.TextIOBase],
     ) -> (Entity, 'Parser'):
-        """Return an entity loaded with a markup file."""
+        """
+        Parse an Entity from a markup language-based launch file.
+
+        Parsers are exposed and provided by available frontend implementations.
+        To choose the right parser, it'll first attempt to infer the launch
+        description format based on the filename extension, if any.
+        If format inference fails, it'll try all available parsers one after the other.
+        """
+        # Imported here, to avoid recursive import.
         cls.load_parser_implementations()
+
+        def get_key(extension):
+            def key(x):
+                return x[0] != extension
+            return key
+        exceptions = []
+        extension = ''
         if is_a(file, str):
-            # This automatically recognizes the launch frontend markup
-            # from the extension.
-            frontend_name = file.rsplit('.', 1)[1]
-            if frontend_name in cls.frontend_parsers:
-                return cls.frontend_parsers[frontend_name].load(file)
-        # If not, apply brute force.
-        # TODO(ivanpauno): Maybe, we want to force correct file naming.
-        # In that case, we should raise an error here.
-        # TODO(ivanpauno): Recognize a wrong formatted file error from
-        # unknown front-end implementation error.
-        for implementation in cls.frontend_parsers.values():
+            extension = file
+        elif hasattr(file, 'name'):
+            extension = file.name
+        extension = os.path.splitext(extension)[1]
+        if extension:
+            extension = extension[1:]
+        for (frontend_name, implementation) in sorted(
+            cls.frontend_parsers.items(), key=get_key(extension)
+        ):
             try:
                 return implementation.load(file)
-            except Exception:
+            except Exception as ex:
                 if is_a(file, io.TextIOBase):
                     file.seek(0)
-        raise RuntimeError('Not recognized front-end implementation.')
+                else:
+                    exceptions.append(ex)
+        extension = '' if not cls.is_extension_valid(extension) else extension
+        raise InvalidFrontendLaunchFileError(extension, likely_errors=exceptions)

launch/launch/invalid_launch_file_error.py

@@ -0,0 +1,41 @@
+# Copyright 2019 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Implementation of `InvalidLaunchFileError` class."""
+
+
+class InvalidLaunchFileError(Exception):
+    """Exception raised when the given launch file is not valid."""
+
+    def __init__(self, extension='', *, likely_errors=None):
+        """Constructor."""
+        self._extension = extension
+        self._likely_errors = likely_errors
+
+    def __str__(self):
+        """Pretty print."""
+        if self._extension == '' or not self._likely_errors:
+            return 'The launch file may have a syntax error, or its format is unknown'
+        else:
+            # If `self.likely_errors[0]` is `RuntimeError('asd')`, the following will be printed:
+            #   ```
+            #   InvalidLaunchFileError: Failed to load file of format [<extension>]:
+            #       RuntimeError: asd
+            #   ```
+            return 'Failed to load file of format [{}]:\n\t{}: {}'.format(
+                self._extension,
+                # Convert `<class 'ERROR_NAME'>` to `ERROR_NAME`
+                str(self._likely_errors[0].__class__)[8:-2],
+                str(self._likely_errors[0])
+            )

launch/launch/launch_description_sources/__init__.py

@@ -15,14 +15,22 @@
 """Package for launch_description_sources."""
 
 from .any_launch_description_source import AnyLaunchDescriptionSource
+from .any_launch_file_utilities import get_launch_description_from_any_launch_file
 from .frontend_launch_description_source import FrontendLaunchDescriptionSource
+from .frontend_launch_file_utilities import get_launch_description_from_frontend_launch_file
+from .frontend_launch_file_utilities import InvalidFrontendLaunchFileError
 from .python_launch_description_source import PythonLaunchDescriptionSource
 from .python_launch_file_utilities import get_launch_description_from_python_launch_file
 from .python_launch_file_utilities import InvalidPythonLaunchFileError
 from .python_launch_file_utilities import load_python_launch_file_as_module
+from ..invalid_launch_file_error import InvalidLaunchFileError
 
 __all__ = [
+    'get_launch_description_from_any_launch_file',
     'get_launch_description_from_python_launch_file',
+    'get_launch_description_from_frontend_launch_file',
+    'InvalidFrontendLaunchFileError',
+    'InvalidLaunchFileError',
     'InvalidPythonLaunchFileError',
     'load_python_launch_file_as_module',
     'AnyLaunchDescriptionSource',

launch/launch/launch_description_sources/any_launch_description_source.py

@@ -14,9 +14,7 @@
 
 """Module for the AnyLaunchDescriptionSource class."""
 
-from .python_launch_file_utilities import get_launch_description_from_python_launch_file
-from .python_launch_file_utilities import InvalidPythonLaunchFileError
-from ..frontend import Parser
+from .any_launch_file_utilities import get_launch_description_from_any_launch_file
 from ..launch_description_source import LaunchDescriptionSource
 from ..some_substitutions_type import SomeSubstitutionsType
 
@@ -25,8 +23,9 @@ class AnyLaunchDescriptionSource(LaunchDescriptionSource):
     """
     Encapsulation of a launch file, which can be loaded during launch.
 
-    This launch description source will attempt to load the file at the given location as a python
-    launch file first, and as a declarative (markup based) launch file if the former fails.
+    This launch description source will attempt to load a launch file based on its extension
+    first, then it will try to load the file as a python launch file, and then as a declarative
+    (markup based) launch file.
     It is recommended to use specific `LaunchDescriptionSource` subclasses when possible.
     """
 
@@ -51,16 +50,4 @@ def __init__(
 
     def _get_launch_description(self, location):
         """Get the LaunchDescription from location."""
-        launch_description = None
-        try:
-            launch_description = get_launch_description_from_python_launch_file(location)
-        except (InvalidPythonLaunchFileError, SyntaxError):
-            pass
-        try:
-            root_entity, parser = Parser.load(location)
-            launch_description = parser.parse_description(root_entity)
-        except RuntimeError:
-            pass
-        if launch_description is None:
-            raise RuntimeError('Cannot load launch file')
-        return launch_description
+        return get_launch_description_from_any_launch_file(location)

launch/launch/launch_description_sources/any_launch_file_utilities.py

@@ -0,0 +1,56 @@
+# Copyright 2019 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Python package utility functions related to loading Frontend Launch Files."""
+
+import os
+from typing import Text
+from typing import Type
+
+from .frontend_launch_file_utilities import get_launch_description_from_frontend_launch_file
+from .python_launch_file_utilities import get_launch_description_from_python_launch_file
+from ..frontend import Parser
+from ..invalid_launch_file_error import InvalidLaunchFileError
+from ..launch_description import LaunchDescription
+
+
+def get_launch_description_from_any_launch_file(
+    launch_file_path: Text,
+    *,
+    parser: Type[Parser] = Parser
+) -> LaunchDescription:
+    """
+    Load a given launch file (by path), and return the launch description from it.
+
+    :raise `InvalidLaunchFileError`: Failed to load launch file.
+        It's only showed with launch files without extension (or not recognized extensions).
+    :raise `SyntaxError`: Invalid file. The file may have a syntax error in it.
+    :raise `ValueError`: Invalid file. The file may not be a text file.
+    """
+    loaders = [get_launch_description_from_frontend_launch_file]
+    extension = os.path.splitext(launch_file_path)[1]
+    if extension:
+        extension = extension[1:]
+    if extension == 'py':
+        loaders.insert(0, get_launch_description_from_python_launch_file)
+    else:
+        loaders.append(get_launch_description_from_python_launch_file)
+    extension = '' if not Parser.is_extension_valid(extension) else extension
+    exceptions = []
+    for loader in loaders:
+        try:
+            return loader(launch_file_path)
+        except Exception as ex:
+            exceptions.append(ex)
+    raise InvalidLaunchFileError(extension, likely_errors=exceptions)

launch/launch/launch_description_sources/frontend_launch_description_source.py

@@ -16,6 +16,7 @@
 
 from typing import Type
 
+from .frontend_launch_file_utilities import get_launch_description_from_frontend_launch_file
 from ..frontend import Parser
 from ..launch_description_source import LaunchDescriptionSource
 from ..some_substitutions_type import SomeSubstitutionsType
@@ -51,8 +52,8 @@ def __init__(
             launch_file_path,
             method
         )
+        self._parser = Parser
 
     def _get_launch_description(self, location):
         """Get the LaunchDescription from location."""
-        root_entity, parser = Parser.load(location)
-        return parser.parse_description(root_entity)
+        return get_launch_description_from_frontend_launch_file(location, parser=self._parser)

launch/launch/launch_description_sources/frontend_launch_file_utilities.py

@@ -0,0 +1,35 @@
+# Copyright 2019 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Python package utility functions related to loading Frontend Launch Files."""
+
+from typing import Text
+from typing import Type
+
+from ..frontend import InvalidFrontendLaunchFileError
+from ..frontend import Parser
+from ..launch_description import LaunchDescription
+
+# Re-export name
+InvalidFrontendLaunchFileError = InvalidFrontendLaunchFileError
+
+
+def get_launch_description_from_frontend_launch_file(
+    frontend_launch_file_path: Text,
+    *,
+    parser: Type[Parser] = Parser
+) -> LaunchDescription:
+    """Load a `LaunchDescription` from a declarative (markup based) launch file."""
+    root_entity, parser = parser.load(frontend_launch_file_path)
+    return parser.parse_description(root_entity)

launch/launch/launch_description_sources/python_launch_description_source.py

@@ -45,4 +45,7 @@ def __init__(
             launch_file_path,
             'interpreted python launch file'
         )
-        self._get_launch_description = get_launch_description_from_python_launch_file
+
+    def _get_launch_description(self, location):
+        """Get the LaunchDescription from location."""
+        return get_launch_description_from_python_launch_file(location)