Merge pull request #1 from Shoobx/lregebro-investigations

Support for type inference by implementedBy/providedBy

README.md

@@ -112,6 +112,17 @@ Type of the `adapter` variable will be set to `IEUPowerSocket`.
 `zope.schema` packages. They are enabled automatically as soon as plugin is
 enabled.
 
+### Conditional type inference
+
+When using `zope.interface`'s `implementedBy()` and `providedBy()` methods
+in an if statement, `mypy` will know which type it is inside those statements.
+
+```python
+if IAnimal.providedBy(ob):
+    ob.number_of_legs += 2
+
+```
+
 ## What is not supported?
 
 These `zope.interface` features are not supported:

src/mypy_zope/plugin.py

@@ -21,7 +21,7 @@
 
 from mypy.nodes import (
     Decorator, Var, Argument, FuncDef, CallExpr, RefExpr, Expression,
-    ClassDef, Statement, Block, IndexExpr,
+    ClassDef, Statement, Block, IndexExpr, MemberExpr,
     MDEF, ARG_POS, ARG_OPT
 )
 
@@ -104,6 +104,21 @@ def get_method_signature_hook(self, fullname: str
     def get_method_hook(self, fullname: str
                         ) -> Optional[Callable[[MethodContext], Type]]:
         # print(f"get_method_hook: {fullname}")
+
+        methodname = fullname.split('.')[-1]
+        if methodname in ('providedBy', 'implementedBy'):
+            def analyze(method_ctx: MethodContext) -> Type:
+                assert isinstance(method_ctx.context, CallExpr)
+                assert isinstance(method_ctx.context.callee, MemberExpr)
+                if method_ctx.context.callee.name == 'providedBy':
+                    method_ctx.context.callee.fullname = 'builtins.isinstance'
+                else:
+                    method_ctx.context.callee.fullname = 'builtins.issubclass'
+                method_ctx.context.args = [method_ctx.args[0][0],
+                                           method_ctx.context.callee.expr]
+
+                return method_ctx.default_return_type
+            return analyze
         return None
 
     def get_attribute_hook(self, fullname: str

src/mypy_zope/stubs/zope/interface/interface.pyi

@@ -23,9 +23,9 @@ class Element:
     def setTaggedValue(self, tag: Any, value: Any) -> None: ...
 
 class SpecificationBasePy:
-    def providedBy(self, ob: Any): ...
-    def implementedBy(self, cls: Any): ...
-    def isOrExtends(self, interface: Any): ...
+    def providedBy(self, ob: Any) -> bool: ...
+    def implementedBy(self, cls: Any) -> bool: ...
+    def isOrExtends(self, interface: Any) -> bool: ...
     __call__: Any = ...
 SpecificationBase = SpecificationBasePy
 
@@ -36,8 +36,6 @@ InterfaceBase = InterfaceBasePy
 adapter_hooks: Any
 
 class Specification(SpecificationBase):
-    isOrExtends: Any = ...
-    providedBy: Any = ...
     dependents: Any = ...
     __bases__: Any = ...
     def __init__(self, bases: Any = ...) -> None: ...

tests/samples/interface_implications.py

@@ -0,0 +1,43 @@
+"""zope.interface provides an abstract attribute for classes
+
+It is translated to Any type.
+"""
+import zope.interface
+from typing import Optional
+
+class IBookmark(zope.interface.Interface):
+    field = zope.interface.Attribute('Arbitrary Attribute')
+
+
+@zope.interface.implementer(IBookmark)
+class Bookmark(object):
+    pass
+
+def main(obj: Optional[IBookmark]) -> None:
+
+    if not IBookmark.providedBy(obj):
+        reveal_type(obj)
+    else:
+        reveal_type(obj)
+    reveal_type(obj)
+
+    cls = obj.__class__
+    if IBookmark.implementedBy(cls):
+        reveal_type(cls)
+    else:
+        reveal_type(cls)
+    reveal_type(cls)
+
+if __name__ == '__main__':
+    main(Bookmark())
+
+"""
+<output>
+interface_implications.py:19: error: Revealed type is 'None'
+interface_implications.py:21: error: Revealed type is '__main__.IBookmark'
+interface_implications.py:22: error: Revealed type is 'Union[__main__.IBookmark, None]'
+interface_implications.py:26: error: Revealed type is 'Type[__main__.IBookmark]'
+interface_implications.py:28: error: Revealed type is 'Union[Type[__main__.IBookmark], Type[None]]'
+interface_implications.py:29: error: Revealed type is 'Union[Type[__main__.IBookmark], Type[None]]'
+</output>
+"""