Clearer error message if cargo.toml is not found (#10)

* Clearer error message if cargo.toml is not found

Currently if a `Cargo.toml` is missing or has the wrong name, the error
message is not very clearly formatted. This PR will give a clear log
output if `ament_cargo` is selected and we are missing a `Cargo.toml`.

Signed-off-by: Arjo Chakravarty <[email protected]>
Signed-off-by: Luca Della Vedova <[email protected]>
Co-authored-by: Luca Della Vedova <[email protected]>

Author: arjo129

colcon_ros_cargo/package_identification/ament_cargo.py

@@ -1,12 +1,16 @@
 # Licensed under the Apache License, Version 2.0
 
+from catkin_pkg.package import parse_package
 from colcon_cargo.package_identification.cargo \
     import CargoPackageIdentification
+from colcon_core.logging import colcon_logger
 from colcon_core.package_identification \
     import PackageIdentificationExtensionPoint
 from colcon_core.plugin_system import satisfies_version
 from colcon_ros.package_identification.ros import _get_package
 
+logger = colcon_logger.getChild(__name__)
+
 
 class AmentCargoPackageIdentification(CargoPackageIdentification):
     """Identify Cargo packages with `Cargo.toml` and `package.xml` files."""
@@ -20,17 +24,25 @@ def __init__(self):  # noqa: D107
             '^1.0')
 
     def identify(self, metadata):  # noqa: D102
-        if metadata.type is not None and metadata.type != 'ament_cargo':
-            return
 
-        cargo_toml = metadata.path / 'Cargo.toml'
-        if not cargo_toml.is_file():
+        if metadata.type is not None and metadata.type != 'ament_cargo':
             return
 
         package_xml = metadata.path / 'package.xml'
         if not package_xml.is_file():
             return
 
+        pkg_desc = parse_package(package_xml)
+
+        if pkg_desc.get_build_type() != 'ament_cargo':
+            return
+
+        cargo_toml = metadata.path / 'Cargo.toml'
+        if not cargo_toml.is_file():
+            logger.warn(
+                'Got build type ament_cargo but could not find "Cargo.toml"')
+            return
+
         metadata.type = 'ament_cargo'
         pkg = _get_package(str(metadata.path))