protocol cache (#450)

From #430

docs/changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Cache decisions about whether classes implement protocols (#450)
 - Fix application of multiple suggested changes per file
   when an earlier change has added or removed lines (#449)
 - Treat `NoReturn` like `Any` in `**kwargs` calls (#446)

pyanalyze/name_check_visitor.py

@@ -2050,10 +2050,10 @@ def _maybe_record_usages_from_import(self, node: ast.ImportFrom) -> None:
                 module_name = parent_module_name + "." + node.module
             else:
                 module_name = parent_module_name
+        if module_name is None:
+            return
         module = sys.modules.get(module_name)
         if module is None:
-            if module_name is None:
-                return
             try:
                 module = __import__(module_name)
             except Exception:

pyanalyze/signature.py

@@ -377,7 +377,7 @@ class ParameterKind(enum.Enum):
 }
 
 
-@dataclass
+@dataclass(frozen=True)
 class SigParameter:
     """Represents a single parameter to a callable."""
 
@@ -411,7 +411,7 @@ class SigParameter:
     def __post_init__(self) -> None:
         # backward compatibility
         if self.default is EMPTY:
-            self.default = None
+            object.__setattr__(self, "default", None)
 
     def substitute_typevars(self, typevars: TypeVarMap) -> "SigParameter":
         return SigParameter(
@@ -519,6 +519,20 @@ def __post_init__(self) -> None:
         )
         self.validate()
 
+    def __hash__(self) -> int:
+        return hash(
+            (
+                tuple(self.parameters.items()),
+                self.return_value,
+                self.impl,
+                self.callable,
+                self.is_asynq,
+                self.has_return_annotation,
+                self.allow_call,
+                self.evaluator,
+            )
+        )
+
     def validate(self) -> None:
         seen_kinds = set()
         seen_with_default = set()

pyanalyze/type_object.py

@@ -5,7 +5,7 @@
 """
 from dataclasses import dataclass, field
 import inspect
-from typing import Container, Set, Sequence, Union
+from typing import Container, Dict, Set, Sequence, Union
 from unittest import mock
 
 from .safe import safe_isinstance, safe_issubclass, safe_in
@@ -15,6 +15,7 @@
     CanAssignContext,
     CanAssignError,
     KnownValue,
+    TypeVarMap,
     TypedValue,
     Value,
     stringify_object,
@@ -42,6 +43,9 @@ class TypeObject:
     protocol_members: Set[str] = field(default_factory=set)
     is_thrift_enum: bool = field(init=False)
     is_universally_assignable: bool = field(init=False)
+    _protocol_positive_cache: Dict[Value, TypeVarMap] = field(
+        default_factory=dict, repr=False
+    )
 
     def __post_init__(self) -> None:
         if isinstance(self.typ, str):
@@ -121,6 +125,9 @@ def can_assign(
                 return CanAssignError(
                     f"Cannot assign super object {other_val} to protocol {self}"
                 )
+            tv_map = self._protocol_positive_cache.get(other_val)
+            if tv_map is not None:
+                return tv_map
             # This is a guard against infinite recursion if the Protocol is recursive
             if ctx.can_assume_compatibility(self, other):
                 return {}
@@ -141,7 +148,9 @@ def can_assign(
                             f"Value of protocol member {member!r} conflicts", [tv_map]
                         )
                     tv_maps.append(tv_map)
-            return unify_typevar_maps(tv_maps)
+            result = unify_typevar_maps(tv_maps)
+            self._protocol_positive_cache[other_val] = result
+            return result
 
     def is_instance(self, obj: object) -> bool:
         """Whether obj is an instance of this type."""