Add PluginManifest.properties for cross-plugin configuration

npe2/_plugin_manager.py

@@ -531,6 +531,40 @@ def get_writer(
         # Nothing got found
         return None, path
 
+    # Accessing Contributions
+
+    def properties(self, config_key: str) -> Set[Any]:
+        """
+        Get plugin properties specifications for the provided key
+
+        Properties are NOT merged until this method is called, and the state is
+        not saved. This lazy properties discovery is preferrable as it ensures
+        that the returned list is consistent with the list of registered plugins.
+
+        Parameters
+        ----------
+        config_key : str
+            Key specified by plugin(s)
+
+        Returns
+        -------
+        Set[Any]
+            All values specified by all plugins for key config_key
+        """
+
+        properties_values: Set[Any] = set()
+        # Search all manifests for the presence of config key
+        for manifest in self._manifests.values():
+            if config_key not in manifest.properties:
+                continue
+            value = manifest.properties[config_key]
+            if isinstance(value, Iterable) and not isinstance(value, str):
+                properties_values.update(value)
+            else:
+                properties_values.add(value)
+
+        return properties_values
+
 
 class PluginContext:
     """An object that can contain information for a plugin over its lifetime."""

npe2/manifest/schema.py

@@ -6,7 +6,7 @@
 from logging import getLogger
 from pathlib import Path
 from textwrap import dedent
-from typing import Iterator, NamedTuple, Optional, Sequence, Union
+from typing import Any, Dict, Iterator, NamedTuple, Optional, Sequence, Union
 
 from pydantic import Extra, Field, ValidationError, root_validator, validator
 from pydantic.error_wrappers import ErrorWrapper
@@ -126,6 +126,13 @@ class Config:
         exclude=True,
     )
 
+    properties: Dict[str, Any] = Field(
+        default={},
+        description="Properties for global values."
+        "May be appended to by other plugins"
+        "who wish to have a say in shared state",
+    )
+
     def __init__(self, **data):
         super().__init__(**data)
         if self.package_metadata is None and self.name:

tests/sample/my_plugin/napari.yaml

@@ -91,3 +91,15 @@ contributions:
     - display_name: Random internet image
       key: internet_image
       uri: https://picsum.photos/1024
+properties:
+  check_num: 10
+  check_num_list:
+    - 1
+    - 2
+    - 3
+  check_str: 'foo'
+  check_str_list:
+    - 'a'
+    - 'b'
+    - 'c'
+  check_bool: true

tests/test_configuration.py

@@ -0,0 +1,64 @@
+from npe2 import PluginManager
+from npe2.manifest.schema import PluginManifest
+
+SAMPLE_PLUGIN_NAME = "my-plugin"
+
+
+def test_properties_empty():
+    """Ensures unpopulated properties before plugin discovery."""
+    pm = PluginManager()
+    assert pm.properties("check_str") == set()
+
+
+def test_properties_single_plugin(sample_manifest):
+    """Ensures populated properties after plugin registry."""
+    pm = PluginManager()
+    pm.register(sample_manifest)
+    assert pm.properties("check_str") == {"foo"}
+    assert pm.properties("check_str_list") == {"a", "b", "c"}
+    assert pm.properties("check_num") == {10}
+    assert pm.properties("check_num_list") == {1, 2, 3}
+    assert pm.properties("check_bool") == {True}
+
+
+def test_properties_single_plugin_unregister(sample_manifest):
+    """Ensures unpopulated properties after plugin unregistry."""
+    pm = PluginManager()
+    pm.register(sample_manifest)
+    pm.unregister("my-plugin")
+    assert pm.properties("check_str") == set()
+
+
+def test_properties_multiple_plugins(sample_manifest):
+    """Ensures population for multiple plugins"""
+    pm = PluginManager()
+
+    # Add a plugin
+    pm.register(sample_manifest)
+    assert pm.properties("check_str") == {"foo"}
+
+    # Add a second plugin
+    manifest2 = PluginManifest(name="my-second-plugin", properties={"check_str": "bar"})
+    pm.register(manifest2)
+    # Ensure its properties is appended
+    assert pm.properties("check_str") == {"foo", "bar"}
+
+    # Add a third plugin
+    manifest3 = PluginManifest(name="my-third-plugin", properties={"check_str": "foo"})
+    pm.register(manifest3)
+    # Ensure its properties is merged
+    assert pm.properties("check_str") == {"foo", "bar"}
+
+
+def test_properties_not_added(sample_manifest):
+    """Ensures unpopulation for unused property"""
+    pm = PluginManager()
+
+    # Add a plugin
+    pm.register(sample_manifest)
+    assert pm.properties("not_added") == set()
+
+    # Add a third plugin
+    manifest2 = PluginManifest(name="my-third-plugin")
+    pm.register(manifest2)
+    assert pm.properties("not_added") == set()