Detect incorrect key types passed to dict.__getitem__

docs/changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Detect incorrect key types passed to `dict.__getitem__` (#468)
 - Pick up the signature of `open()` from typeshed correctly (#463)
 - Do not strip away generic parameters explicitly set to
   `Any` (#467)

pyanalyze/implementation.py

@@ -535,6 +535,15 @@ def inner(key: Value) -> Value:
                 return AnyValue(AnySource.error)
             return val
         elif isinstance(self_value, TypedValue):
+            key_type = self_value.get_generic_arg_for_type(dict, ctx.visitor, 0)
+            can_assign = key_type.can_assign(key, ctx.visitor)
+            if isinstance(can_assign, CanAssignError):
+                ctx.show_error(
+                    f"Dictionary does not accept keys of type {key}",
+                    error_code=ErrorCode.incompatible_argument,
+                    detail=str(can_assign),
+                    arg="key",
+                )
             return self_value.get_generic_arg_for_type(dict, ctx.visitor, 1)
         else:
             return AnyValue(AnySource.inference)

pyanalyze/stacked_scopes.py

@@ -947,8 +947,8 @@ class FunctionScope(Scope):
     name_to_current_definition_nodes: SubScope
     usage_to_definition_nodes: Dict[Tuple[Node, Varname], List[Node]]
     definition_node_to_value: Dict[Node, Value]
-    name_to_all_definition_nodes: Dict[str, Set[Node]]
-    name_to_composites: Dict[str, Set[CompositeVariable]]
+    name_to_all_definition_nodes: Dict[Varname, Set[Node]]
+    name_to_composites: Dict[Varname, Set[CompositeVariable]]
     referencing_value_vars: Dict[Varname, Value]
     accessed_from_special_nodes: Set[Varname]
     current_loop_scopes: List[SubScope]

pyanalyze/test_implementation.py

@@ -1078,6 +1078,8 @@ def capybara(
             assert_is_value(nd[1], TypedValue(str))
             assert_is_value(rev[1], TypedValue(str))
 
+            dct[1]  # E: incompatible_argument
+
 
 class TestDictSetItem(TestNameCheckVisitorBase):
     @assert_passes()