Add package version to metadata (#45)

The package version is typically read during the augmentation phase,
but this package doesn't have one (yet). Since the dependencies are
already being read during identification, go ahead and read the version
then as well.

colcon_cargo/package_identification/cargo.py

@@ -50,6 +50,8 @@ def identify(self, metadata):  # noqa: D102
         metadata.type = 'cargo'
         if metadata.name is None:
             metadata.name = data['name']
+        metadata.metadata['version'] = data['version']
+
         metadata.dependencies['build'] |= data['depends']
         metadata.dependencies['run'] |= data['depends']
 
@@ -78,6 +80,7 @@ def extract_data(cargo_toml):
     toml_name_attr = extract_project_name(content)
     data['name'] = toml_name_attr if toml_name_attr is not None else \
         cargo_toml.parent.name
+    data['version'] = extract_project_version(content)
 
     depends = extract_dependencies(content)
     # exclude self references
@@ -100,6 +103,20 @@ def extract_project_name(content):
         return None
 
 
+def extract_project_version(content):
+    """
+    Extract the Cargo project version from the Cargo.toml file.
+
+    :param str content: The Cargo.toml parsed dictionary
+    :returns: The project version, otherwise None
+    :rtype: str
+    """
+    try:
+        return content['package']['version']
+    except KeyError:
+        return None
+
+
 def extract_dependencies(content):
     """
     Extract the dependencies from the Cargo.toml file.