Extract target-specific dependencies as well (#57)

It appears that cargo will look for target-specific dependencies even
when the dependencies do not apply to the current platform. This saves
us the trouble of parsing the `cfg()` logic.

Author: cottsay

colcon_cargo/package_augmentation/cargo.py

@@ -48,6 +48,11 @@ def _augment_package(
         for k, v in dependencies.items():
             metadata.dependencies[k] |= v
 
+        for category, spec in content.get('target', {}).items():
+            dependencies = extract_dependencies(spec, metadata.path)
+            for k, v in dependencies.items():
+                metadata.dependencies[k] |= v
+
         authors = package.get('authors', ())
         if authors:
             metadata.metadata.setdefault('maintainers', [])

test/rust-sample-package/Cargo.toml

@@ -8,3 +8,6 @@ edition = "2018"
 
 [dependencies]
 local-rust-pure-library = {package = "rust-pure-library", path = "../rust-pure-library"}
+
+[target.'cfg(windows)'.dependencies]
+windows-sys = "0.59"

test/test_build.py

@@ -47,6 +47,7 @@ def test_package_identification():
 def test_package_augmentation():
     cpi = CargoPackageIdentification()
     aug = CargoPackageAugmentation()
+
     desc = PackageDescriptor(pure_library_path)
     cpi.identify(desc)
     aug.augment_package(desc)
@@ -58,6 +59,15 @@ def test_package_augmentation():
     assert 'either' in desc.dependencies['build']
     assert desc.dependencies['run'] == desc.dependencies['build']
 
+    desc = PackageDescriptor(test_project_path)
+    cpi.identify(desc)
+    aug.augment_package(desc)
+    print(desc)
+    assert len(desc.dependencies['build']) == 2
+    assert PURE_LIBRARY_PACKAGE_NAME in desc.dependencies['build']
+    assert 'windows-sys' in desc.dependencies['build']
+    assert desc.dependencies['run'] == desc.dependencies['build']
+
 
 # Ported from Python 3.13 implementation
 # Remove when migrating to Python 3.13 and above
@@ -87,9 +97,11 @@ def test_path_dependencies():
     desc = PackageDescriptor(test_project_path)
     cpi.identify(desc)
     aug.augment_package(desc)
-    assert PURE_LIBRARY_PACKAGE_NAME in desc.dependencies['build']
-    assert len(desc.dependencies['build']) == 1
-    dep = desc.dependencies['build'].pop()
+    for dep in desc.dependencies['build']:
+        if dep.name == PURE_LIBRARY_PACKAGE_NAME:
+            break
+    else:
+        assert False, f'{PURE_LIBRARY_PACKAGE_NAME} not in build deps'
     assert 'cargo_source' in dep.metadata
     assert dep.metadata['cargo_source'] is not None
     # Path.from_uri was only added in Python 3.13