Check against invalid Signature objects and prepare for refactoring Signature compatibility logic

docs/changelog.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Check against invalid `Signature` objects and prepare
+  for refactoring `Signature` compatibility logic (#390)
 - Treat `int` and `float` as compatible with `complex`,
   as specified in PEP 484 (#389)
 - Do not error on boolean operations on values typed

pyanalyze/arg_spec.py

@@ -60,7 +60,17 @@
 import inspect
 import sys
 from types import FunctionType, ModuleType
-from typing import Any, Callable, Iterator, Sequence, Generic, Mapping, Optional, Union
+from typing import (
+    Any,
+    Callable,
+    Iterator,
+    Sequence,
+    Generic,
+    Mapping,
+    Optional,
+    Tuple,
+    Union,
+)
 import typing_inspect
 from unittest import mock
 
@@ -352,11 +362,15 @@ def from_signature(
 
         parameters = []
         for i, parameter in enumerate(sig.parameters.values()):
-            parameters.append(
-                self._make_sig_parameter(
-                    parameter, func_globals, function_object, is_wrapped, i
-                )
+            param, make_everything_pos_only = self._make_sig_parameter(
+                parameter, func_globals, function_object, is_wrapped, i
             )
+            if make_everything_pos_only:
+                parameters = [
+                    replace(param, kind=ParameterKind.POSITIONAL_ONLY)
+                    for param in parameters
+                ]
+            parameters.append(param)
 
         return Signature.make(
             parameters,
@@ -376,7 +390,7 @@ def _make_sig_parameter(
         function_object: Optional[object],
         is_wrapped: bool,
         index: int,
-    ) -> SigParameter:
+    ) -> Tuple[SigParameter, bool]:
         """Given an inspect.Parameter, returns a Parameter object."""
         if is_wrapped:
             typ = AnyValue(AnySource.inference)
@@ -395,9 +409,14 @@ def _make_sig_parameter(
             )
         ):
             kind = ParameterKind.POSITIONAL_ONLY
+            make_everything_pos_only = True
         else:
             kind = ParameterKind(parameter.kind)
-        return SigParameter(parameter.name, kind, default=default, annotation=typ)
+            make_everything_pos_only = False
+        return (
+            SigParameter(parameter.name, kind, default=default, annotation=typ),
+            make_everything_pos_only,
+        )
 
     def _get_type_for_parameter(
         self,

pyanalyze/functions.py

@@ -246,14 +246,19 @@ def compute_parameters(
 
     posonly_args = getattr(node.args, "posonlyargs", [])
     num_without_defaults = len(node.args.args) + len(posonly_args) - len(defaults)
-    defaults = [*[None] * num_without_defaults, *defaults, *kw_defaults]
-    args: List[Tuple[ParameterKind, ast.arg]] = (
-        [(ParameterKind.POSITIONAL_ONLY, arg) for arg in posonly_args]
-        + [(ParameterKind.POSITIONAL_OR_KEYWORD, arg) for arg in node.args.args]
-        + [(ParameterKind.KEYWORD_ONLY, arg) for arg in node.args.kwonlyargs]
-    )
+    vararg_defaults = [None] if node.args.vararg is not None else []
+    defaults = [
+        *[None] * num_without_defaults,
+        *defaults,
+        *vararg_defaults,
+        *kw_defaults,
+    ]
+    args: List[Tuple[ParameterKind, ast.arg]] = [
+        (ParameterKind.POSITIONAL_ONLY, arg) for arg in posonly_args
+    ] + [(ParameterKind.POSITIONAL_OR_KEYWORD, arg) for arg in node.args.args]
     if node.args.vararg is not None:
         args.append((ParameterKind.VAR_POSITIONAL, node.args.vararg))
+    args += [(ParameterKind.KEYWORD_ONLY, arg) for arg in node.args.kwonlyargs]
     if node.args.kwarg is not None:
         args.append((ParameterKind.VAR_KEYWORD, node.args.kwarg))
     params = []