fix type errors (#3928)

* fix type checking error in overriding path propery

* fix type hints in sew stack

* enable type checking for tartan

* ignore type warnings for dynamic wx module attributes

* fix tartan type errors

* fix circular import

* add type-check and test targets

* use Optional instead

3 files changed, 55 insertions, 15 deletions

diff --git a/lib/sew_stack/stitch_layers/mixins/path.py b/lib/sew_stack/stitch_layers/mixins/path.py
index 88e5419d..9739f381 100644
--- a/lib/sew_stack/stitch_layers/mixins/path.py
+++ b/lib/sew_stack/stitch_layers/mixins/path.py
@@ -1,6 +1,6 @@
+from .protocol import LayerProtocol
 from ..stitch_layer_editor import Category, Property
 from ....i18n import _
-from ....utils import DotDict, Point
 
 
 class PathPropertiesMixin:
@@ -13,10 +13,7 @@ class PathPropertiesMixin:
 
 
 class PathMixin:
-    config: DotDict
-    paths: 'list[list[Point]]'
-
-    def get_paths(self):
+    def get_paths(self: LayerProtocol):
         paths = self.paths
 
         if self.config.reverse_path:
diff --git a/lib/sew_stack/stitch_layers/mixins/protocol.py b/lib/sew_stack/stitch_layers/mixins/protocol.py
new file mode 100644
index 00000000..1057bd7b
--- /dev/null
+++ b/lib/sew_stack/stitch_layers/mixins/protocol.py
@@ -0,0 +1,50 @@
+from typing import Protocol, TYPE_CHECKING
+
+from lib.utils import DotDict, Point
+
+
+if TYPE_CHECKING:
+    from lib.sew_stack import SewStack
+
+
+class LayerProtocol(Protocol):
+    paths: 'list[list[Point]]'
+    config: DotDict
+    element: 'SewStack'
+
+
+def with_protocol(protocol):
+    """Include a protocol in a Mixin only for type hinting.
+
+    Normally we'd use a protocol in a mixin to indicate that we
+    expect certain attributes to be available on self, as
+    described here:
+
+    https://mypy.readthedocs.io/en/stable/more_types.html#mixin-classes
+
+    However, for some reason type-checkers then _only_ allow use of
+    properties on self that are defined in the protocol.  For example,
+    this doesn't work:
+
+    class MyMixin:
+        def foo(self):
+            return "hi"
+
+        def bar(self: LayerProtocol):
+            thing = self.foo()
+            if self.config.baz == thing:
+                ...
+
+    This fails because mypy says that "self.foo()" references unknown
+    attribute "foo"... even though it's defined right there in MyMixin.
+    This feels a little weird, but that's how it works.
+
+    Instead, we do it like this:
+
+    class MyMixin(with_protocol(LayerProtocol)):
+        ...
+    """
+    if TYPE_CHECKING:
+        return protocol
+    else:
+        return object
diff --git a/lib/sew_stack/stitch_layers/mixins/randomization.py b/lib/sew_stack/stitch_layers/mixins/randomization.py
index 5414731c..009b5042 100644
--- a/lib/sew_stack/stitch_layers/mixins/randomization.py
+++ b/lib/sew_stack/stitch_layers/mixins/randomization.py
@@ -1,17 +1,13 @@
 import os
 from secrets import randbelow
-from typing import TYPE_CHECKING
 
 import wx.propgrid
 
+from .protocol import LayerProtocol, with_protocol
 from ..stitch_layer_editor import Category, Property
 from ....i18n import _
 from ....svg import PIXELS_PER_MM
-from ....utils import DotDict, get_resource_dir, prng
-
-if TYPE_CHECKING:
-    from ... import SewStack
-
+from ....utils import get_resource_dir, prng
 
 editor_instance = None
 
@@ -70,10 +66,7 @@ class RandomizationPropertiesMixin:
         )
 
 
-class RandomizationMixin:
-    config: DotDict
-    element: "SewStack"
-
+class RandomizationMixin(with_protocol(LayerProtocol)):
     @classmethod
     def randomization_defaults(cls):
         return dict(