Infer precise signatures for TypedDict types

docs/changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Infer precise call signatures for `TypedDict` types (#487)
 - Add mechanism to prevent crashes on objects
   with unusual `__getattr__` methods (#486)
 - Infer callable signatures for objects with a

pyanalyze/arg_spec.py

@@ -42,6 +42,7 @@
     Extension,
     GenericBases,
     KVPair,
+    TypedDictValue,
     TypedValue,
     GenericValue,
     NewTypeValue,
@@ -77,6 +78,7 @@
     Tuple,
     Union,
 )
+from typing_extensions import is_typeddict
 import typing_inspect
 from unittest import mock
 
@@ -645,6 +647,20 @@ def _uncached_get_argspec(
         if argspec is not None:
             return argspec
 
+        if is_typeddict(obj) and not is_typing_name(obj, "TypedDict"):
+            td_type = type_from_runtime(obj)
+            if isinstance(td_type, TypedDictValue):
+                params = [
+                    SigParameter(
+                        key,
+                        ParameterKind.KEYWORD_ONLY,
+                        default=None if required else KnownValue(...),
+                        annotation=value,
+                    )
+                    for key, (required, value) in td_type.items.items()
+                ]
+                return Signature.make(params, td_type)
+
         if is_newtype(obj):
             assert hasattr(obj, "__supertype__")
             return Signature.make(

pyanalyze/test_typeddict.py

@@ -0,0 +1,37 @@
+# static analysis: ignore
+from .implementation import assert_is_value
+from .value import TypedDictValue, TypedValue
+from .test_name_check_visitor import TestNameCheckVisitorBase
+from .test_node_visitor import assert_passes
+
+
+class TestTypedDict(TestNameCheckVisitorBase):
+    @assert_passes()
+    def test_constructor(self):
+        from typing_extensions import TypedDict, NotRequired
+
+        class Capybara(TypedDict):
+            x: int
+            y: str
+
+        class MaybeCapybara(TypedDict):
+            x: int
+            y: NotRequired[str]
+
+        def capybara():
+            cap = Capybara(x=1, y="2")
+            assert_is_value(
+                cap,
+                TypedDictValue(
+                    {"x": (True, TypedValue(int)), "y": (True, TypedValue(str))}
+                ),
+            )
+            Capybara(x=1)  # E: incompatible_call
+
+            maybe_cap = MaybeCapybara(x=1)
+            assert_is_value(
+                maybe_cap,
+                TypedDictValue(
+                    {"x": (True, TypedValue(int)), "y": (False, TypedValue(str))}
+                ),
+            )