fix(python): unable to implement additional interfaces (#2964)

When a type extends a jsii class, any additional interfaces implemented
via the `@jsii.implements` annotation were not properly registered, and
overrides were not properly discovered.

This was the combination of a code-generation bug, which caused the type
passed to the `create` kernel method to be that of the jsii class,
instead of the dynamic class (`self.__class__`); and a kernel bug, which
caused those inheritance graphs to completely skip overrides detection.

Fixes #2963



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/@jsii/python-runtime/src/jsii/_kernel/__init__.py

@@ -63,21 +63,34 @@ def _get_overides(klass: Type, obj: Any) -> List[Override]:
     # We need to inspect each item in the MRO, until we get to our Type, at that
     # point we'll bail, because those methods are not the overriden methods, but the
     # "real" methods.
-    jsii_classes = [klass] + list(
+    jsii_name = getattr(klass, "__jsii_type__", "Object")
+    jsii_classes = [
+        next(
+            (
+                m
+                for m in type(obj).mro()
+                if getattr(m, "__jsii_declared_type__", None) == jsii_name
+            ),
+            Object,
+        )
+    ] + list(
         itertools.chain.from_iterable(
             (getattr(m, "__jsii_ifaces__", []) for m in type(obj).mro())
         )
     )
     for mro_klass in type(obj).mro():
-        if (
-            mro_klass is klass
-            and getattr(mro_klass, "__jsii_type__", "Object") is not None
-        ):
+        if getattr(mro_klass, "__jsii_declared_type__", None) is not None:
+            # There is a jsii declared type, so we reached a "well known" object,
+            # and nothing from now on is an override.
             break
-        if mro_klass is Object:
+        if mro_klass is Object or mro_klass is object:
             break
 
         for name, item in mro_klass.__dict__.items():
+            # Ignore all "special" members (name starting with __)...
+            if name.startswith("__"):
+                continue
+
             # We're only interested in things that also exist on the JSII class or
             # interfaces, and which are themselves, jsii members.
             for jsii_class in jsii_classes:
@@ -93,6 +106,7 @@ def _get_overides(klass: Type, obj: Any) -> List[Override]:
                         overrides.append(
                             Override(method=original.__jsii_name__, cookie=name)
                         )
+                        break
                     elif inspect.isdatadescriptor(item) and hasattr(
                         getattr(original, "fget", None), "__jsii_name__"
                     ):
@@ -105,6 +119,7 @@ def _get_overides(klass: Type, obj: Any) -> List[Override]:
                         overrides.append(
                             Override(property=original.fget.__jsii_name__, cookie=name)
                         )
+                        break
 
     return overrides
 

packages/@jsii/python-runtime/src/jsii/_runtime.py

@@ -68,6 +68,9 @@ def __new__(
         # will as well anyways.
         if jsii_type is not None:
             attrs["__jsii_type__"] = jsii_type
+        # The declared type should NOT be inherited by subclasses. This way we can identify whether
+        # an MRO entry corresponds to a possible overrides contributor or not.
+        attrs["__jsii_declared_type__"] = jsii_type
 
         obj = super().__new__(cls, name, bases, attrs)
 

packages/@jsii/python-runtime/tests/test_compliance.py

@@ -1288,3 +1288,33 @@ def repeat(self, word: str) -> str:
     entropy = MildEntropy(wall_clock)
 
     assert now == entropy.increase()
+
+
+def test_class_can_extend_and_implement_from_jsii():
+    """
+    This test is identical to test_iso8601_does_not_deserialize_to_date, except
+    the WallCloc class extends ClassWithSelf (a well-known jsii type), to
+    demonstrate it is possible to both extend a jsii type, and implement a
+    supplemental interface at the same time.
+
+    See also https://github.com/aws/jsii/issues/2963
+    """
+
+    @jsii.implements(IWallClock)
+    class WallClock(ClassWithSelf):
+        def __init__(self, now: str):
+            super().__init__(now)
+            self.now = now
+
+        def iso8601_now(self) -> str:
+            return self.now
+
+    class MildEntropy(Entropy):
+        def repeat(self, word: str) -> str:
+            return word
+
+    now = datetime.utcnow().isoformat() + "Z"
+    wall_clock = WallClock(now)
+    entropy = MildEntropy(wall_clock)
+
+    assert now == entropy.increase()

packages/jsii-pacmak/lib/targets/python.ts

@@ -455,6 +455,7 @@ abstract class BaseMethod implements PythonBase {
     private readonly parameters: spec.Parameter[],
     private readonly returns: spec.OptionalValue | undefined,
     public readonly docs: spec.Docs | undefined,
+    public readonly isStatic: boolean,
     opts: BaseMethodOpts,
   ) {
     this.abstract = !!opts.abstract;
@@ -710,12 +711,17 @@ abstract class BaseMethod implements PythonBase {
       if (this.parent === undefined) {
         throw new Error('Parent not known.');
       }
-      jsiiMethodParams.push(
-        toTypeName(this.parent).pythonType({
-          ...context,
-          typeAnnotation: false,
-        }),
-      );
+      if (this.isStatic) {
+        jsiiMethodParams.push(
+          toTypeName(this.parent).pythonType({
+            ...context,
+            typeAnnotation: false,
+          }),
+        );
+      } else {
+        // Using the dynamic class of `self`.
+        jsiiMethodParams.push(`${implicitParameter}.__class__`);
+      }
     }
     jsiiMethodParams.push(implicitParameter);
     if (this.jsName !== undefined) {
@@ -2429,6 +2435,7 @@ class PythonGenerator extends Generator {
           parameters,
           undefined,
           cls.initializer.docs,
+          false, // Never static
           { liftedProp: this.getliftedProp(cls.initializer), parent: cls },
         ),
       );
@@ -2448,6 +2455,7 @@ class PythonGenerator extends Generator {
         parameters,
         method.returns,
         method.docs,
+        true, // Always static
         {
           abstract: method.abstract,
           liftedProp: this.getliftedProp(method),
@@ -2487,6 +2495,7 @@ class PythonGenerator extends Generator {
           parameters,
           method.returns,
           method.docs,
+          !!method.static,
           {
             abstract: method.abstract,
             liftedProp: this.getliftedProp(method),
@@ -2503,6 +2512,7 @@ class PythonGenerator extends Generator {
           parameters,
           method.returns,
           method.docs,
+          !!method.static,
           {
             abstract: method.abstract,
             liftedProp: this.getliftedProp(method),
@@ -2578,6 +2588,7 @@ class PythonGenerator extends Generator {
         parameters,
         method.returns,
         method.docs,
+        !!method.static,
         { liftedProp: this.getliftedProp(method), parent: ifc },
       ),
     );