Optional providers, take two (#104)

* Simplify plugin loader to use `providers`

* Add an `optional` key to provider information

Add a boolean `optional` key to provider information that can be used
to specify that a provider is optional and therefore should not be
enabled by default.

* Update test artifacts to test `optional = true` too

* Add plugin loader parameters to enable optional plugins

* Expose `enable_optional_plugins` in API

* Use `VariantNamespace` type for `enable_optional_plugins`

* Handle empty plugin lists gracefully

* Support filtering loaded plugins

* Make `validate_variant()` only load plugins it needs

Author: mgorny

tests/artifacts/test-package/dist/test_package-0-py3-none-any-00000000.whl

@@ -2,14 +2,21 @@
     "$schema": "https://variants-schema.wheelnext.dev/",
     "default-priorities": {
         "namespace": [
-            "installable_plugin"
+            "installable_plugin",
+            "non_existing_plugin"
         ]
     },
     "providers": {
         "installable_plugin": {
             "requires": [
                 "test-plugin-package"
             ]
+        },
+        "non_existing_plugin": {
+            "optional": true,
+            "requires": [
+                "do-not-install-me"
+            ]
         }
     },
     "variants": {

tests/artifacts/test-package/dist/test_package-0-py3-none-any-5d8be4b9.whl

@@ -9,7 +9,12 @@ description = "Installable package for testing"
 requires-python = ">=3.9"
 
 [variant.default-priorities]
-namespace = ["installable_plugin"]
+namespace = ["installable_plugin", "non_existing_plugin"]
 
 [variant.providers.installable_plugin]
 requires = ["test-plugin-package"]
+optional = false
+
+[variant.providers.non_existing_plugin]
+requires = ["do-not-install-me"]
+optional = true

tests/artifacts/test-package/dist/test_package-0-py3-none-any-60567bd9.whl

@@ -8,6 +8,7 @@
 from variantlib.constants import VARIANT_INFO_DEFAULT_PRIO_KEY
 from variantlib.constants import VARIANT_INFO_NAMESPACE_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_DATA_KEY
+from variantlib.constants import VARIANT_INFO_PROVIDER_OPTIONAL_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_REQUIRES_KEY
 from variantlib.constants import VARIANTS_JSON_SCHEMA_KEY
 from variantlib.constants import VARIANTS_JSON_SCHEMA_URL
@@ -32,12 +33,17 @@ def test_generate_index_json(
         VARIANT_INFO_DEFAULT_PRIO_KEY: {
             VARIANT_INFO_NAMESPACE_KEY: [
                 "installable_plugin",
+                "non_existing_plugin",
             ]
         },
         VARIANT_INFO_PROVIDER_DATA_KEY: {
             "installable_plugin": {
                 VARIANT_INFO_PROVIDER_REQUIRES_KEY: ["test-plugin-package"],
             },
+            "non_existing_plugin": {
+                VARIANT_INFO_PROVIDER_REQUIRES_KEY: ["do-not-install-me"],
+                VARIANT_INFO_PROVIDER_OPTIONAL_KEY: True,
+            },
         },
         VARIANTS_JSON_VARIANT_DATA_KEY: {
             "00000000": {},

tests/artifacts/test-package/dist/test_package-0-py3-none-any-fbe82642.whl

@@ -2,6 +2,8 @@
 
 import re
 import sys
+from functools import partial
+from typing import Callable
 
 import pytest
 
@@ -26,6 +28,7 @@
 from variantlib.plugins.loader import PluginLoader
 from variantlib.protocols import PluginType
 from variantlib.protocols import VariantFeatureConfigType
+from variantlib.protocols import VariantNamespace
 from variantlib.pyproject_toml import VariantPyProjectToml
 from variantlib.variants_json import VariantsJson
 
@@ -389,6 +392,7 @@ def test_load_plugin_invalid_arg() -> None:
                 "test_namespace",
                 "second_namespace",
                 "incompatible_namespace",
+                "one_more",
             ],
             providers={
                 "test_namespace": ProviderInfo(
@@ -404,6 +408,10 @@ def test_load_plugin_invalid_arg() -> None:
                     enable_if='platform_machine == "frobnicator"',
                     plugin_api="tests.mocked_plugins:MockedPluginC",
                 ),
+                "one_more": ProviderInfo(
+                    plugin_api="tests.mocked_plugins:NoSuchClass",
+                    optional=True,
+                ),
             },
         ),
         VariantPyProjectToml(
@@ -477,3 +485,91 @@ def test_no_plugin_api(test_plugin_package_req: str) -> None:
 
     with PluginLoader(variant_info, use_auto_install=True, isolated=True) as loader:
         assert set(loader.namespaces) == {"installable_plugin"}
+
+
+@pytest.mark.parametrize(
+    ("value", "expected"),
+    [
+        (False, False),
+        (True, True),
+        ([], False),
+        (["test_namespace"], False),
+        (["second_namespace"], True),
+        (["second_namespace", "test_namespace"], True),
+        (["frobnicate"], False),
+        (["frobnicate", "second_namespace"], True),
+    ],
+)
+def test_optional_plugins(value: bool | list[VariantNamespace], expected: bool) -> None:
+    variant_info = VariantInfo(
+        namespace_priorities=[
+            "test_namespace",
+            "second_namespace",
+        ],
+        providers={
+            "test_namespace": ProviderInfo(
+                plugin_api="tests.mocked_plugins:MockedPluginA"
+            ),
+            "second_namespace": ProviderInfo(
+                plugin_api="tests.mocked_plugins:MockedPluginB", optional=True
+            ),
+        },
+    )
+
+    expected_namespaces = {"test_namespace"}
+    if expected:
+        expected_namespaces.add("second_namespace")
+    with PluginLoader(
+        variant_info, use_auto_install=False, enable_optional_plugins=value
+    ) as loader:
+        assert set(loader.namespaces) == expected_namespaces
+
+
+@pytest.mark.parametrize(
+    "loader_call",
+    [
+        partial(PluginLoader, VariantInfo(), use_auto_install=False),
+        partial(ListPluginLoader, []),
+    ],
+)
+def test_empty_plugin_list(loader_call: Callable[[], BasePluginLoader]) -> None:
+    with loader_call() as loader:
+        assert loader.namespaces == []
+        assert loader.get_supported_configs() == {}
+        assert loader.get_all_configs() == {}
+        assert loader.get_build_setup(VariantDescription([])) == {}
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        [],
+        ["test_namespace"],
+        ["second_namespace"],
+        ["second_namespace", "test_namespace"],
+        ["frobnicate"],
+        ["frobnicate", "second_namespace"],
+    ],
+)
+def test_filter_plugins(value: list[VariantNamespace]) -> None:
+    variant_info = VariantInfo(
+        namespace_priorities=[
+            "test_namespace",
+            "second_namespace",
+        ],
+        providers={
+            "test_namespace": ProviderInfo(
+                plugin_api="tests.mocked_plugins:MockedPluginA"
+            ),
+            "second_namespace": ProviderInfo(
+                plugin_api="tests.mocked_plugins:MockedPluginB"
+            ),
+        },
+    )
+
+    expected_namespaces = set(value)
+    expected_namespaces.discard("frobnicate")
+    with PluginLoader(
+        variant_info, use_auto_install=False, filter_plugins=value
+    ) as loader:
+        assert set(loader.namespaces) == expected_namespaces

tests/artifacts/test-package/dist/test_package-0-py3-none-any.whl

@@ -37,6 +37,7 @@
 from variantlib.constants import VARIANT_INFO_PROPERTY_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_DATA_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_ENABLE_IF_KEY
+from variantlib.constants import VARIANT_INFO_PROVIDER_OPTIONAL_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_PLUGIN_API_KEY
 from variantlib.constants import VARIANT_INFO_PROVIDER_REQUIRES_KEY
 from variantlib.constants import VARIANTS_JSON_SCHEMA_KEY
@@ -268,7 +269,8 @@ def test_validation_result_properties() -> None:
     ]
 
 
-def test_validate_variant(mocked_plugin_apis: list[str]) -> None:
+@pytest.mark.parametrize("optional", [False, True])
+def test_validate_variant(mocked_plugin_apis: list[str], optional: bool) -> None:
     variant_info = VariantInfo(
         namespace_priorities=[
             "test_namespace",
@@ -277,13 +279,13 @@ def test_validate_variant(mocked_plugin_apis: list[str]) -> None:
         ],
         providers={
             "test_namespace": ProviderInfo(
-                plugin_api="tests.mocked_plugins:MockedPluginA"
+                plugin_api="tests.mocked_plugins:MockedPluginA", optional=optional
             ),
             "second_namespace": ProviderInfo(
-                plugin_api="tests.mocked_plugins:MockedPluginB"
+                plugin_api="tests.mocked_plugins:MockedPluginB", optional=optional
             ),
             "incompatible_namespace": ProviderInfo(
-                plugin_api="tests.mocked_plugins:MockedPluginC"
+                plugin_api="tests.mocked_plugins:MockedPluginC", optional=optional
             ),
         },
     )
@@ -360,6 +362,7 @@ def test_make_variant_dist_info(
                         "old_ns2_provider; python_version < '3.11'",
                     ],
                     VARIANT_INFO_PROVIDER_PLUGIN_API_KEY: "ns2_provider:Plugin",
+                    VARIANT_INFO_PROVIDER_OPTIONAL_KEY: True,
                 },
             }
         )