Canonicalize type as type[Any]

This diff canonicalised the builtin type (which is a class) as a
`Type::Type` with an implicit `Any`.

The typing spec
(https://typing.python.org/en/latest/spec/special-types.html#type)
requires that
"Plain `type` without brackets, the root of Python’s metaclass hierarchy,
is equivalent to `type[Any]`."

Whereas assignments of `type` and `type[Any]` are allowed by Pyrefly
before this diff, they are not considered as identical types by
`assert_type` call. After the canonicalisation introduced by this diff,
they are considered as identical. As a result, we are able to pass 3
more conformance test cases.

Since `type` itself is a class, we need to add some special treatment in
the type system on inheritance, so that it can be inherited and used as
a metaclass, while being a `Type::Type`. Some of the treatments are
similar to how `tuple` is handled.

Author: fangyi-zhou

conformance/third_party/conformance.exp

@@ -9865,41 +9865,19 @@
     {
       "code": -2,
       "column": 16,
-      "concise_description": "assert_type(type, type[Any]) failed",
-      "description": "assert_type(type, type[Any]) failed",
-      "line": 84,
+      "concise_description": "assert_type(Any, tuple[type[Any], ...]) failed",
+      "description": "assert_type(Any, tuple[type[Any], ...]) failed",
+      "line": 98,
       "name": "assert-type",
       "severity": "error",
-      "stop_column": 30,
-      "stop_line": 84
-    },
-    {
-      "code": -2,
-      "column": 17,
-      "concise_description": "Object of class `type` has no attribute `unknown`",
-      "description": "Object of class `type` has no attribute `unknown`",
-      "line": 99,
-      "name": "missing-attribute",
-      "severity": "error",
-      "stop_column": 26,
-      "stop_line": 99
-    },
-    {
-      "code": -2,
-      "column": 17,
-      "concise_description": "Object of class `type` has no attribute `unknown`",
-      "description": "Object of class `type` has no attribute `unknown`",
-      "line": 100,
-      "name": "missing-attribute",
-      "severity": "error",
-      "stop_column": 26,
-      "stop_line": 100
+      "stop_column": 45,
+      "stop_line": 98
     },
     {
       "code": -2,
       "column": 16,
-      "concise_description": "assert_type(Any, tuple[type, ...]) failed",
-      "description": "assert_type(Any, tuple[type, ...]) failed",
+      "concise_description": "assert_type(Any, tuple[type[Any], ...]) failed",
+      "description": "assert_type(Any, tuple[type[Any], ...]) failed",
       "line": 102,
       "name": "assert-type",
       "severity": "error",
@@ -9909,8 +9887,8 @@
     {
       "code": -2,
       "column": 16,
-      "concise_description": "assert_type(Any, tuple[type, ...]) failed",
-      "description": "assert_type(Any, tuple[type, ...]) failed",
+      "concise_description": "assert_type(Any, tuple[type[Any], ...]) failed",
+      "description": "assert_type(Any, tuple[type[Any], ...]) failed",
       "line": 106,
       "name": "assert-type",
       "severity": "error",
@@ -9920,8 +9898,8 @@
     {
       "code": -2,
       "column": 16,
-      "concise_description": "assert_type(Any, tuple[type, ...]) failed",
-      "description": "assert_type(Any, tuple[type, ...]) failed",
+      "concise_description": "assert_type(Any, tuple[type[Any], ...]) failed",
+      "description": "assert_type(Any, tuple[type[Any], ...]) failed",
       "line": 110,
       "name": "assert-type",
       "severity": "error",
@@ -9950,22 +9928,11 @@
       "stop_column": 14,
       "stop_line": 120
     },
-    {
-      "code": -2,
-      "column": 16,
-      "concise_description": "assert_type(type, type[Any]) failed",
-      "description": "assert_type(type, type[Any]) failed",
-      "line": 139,
-      "name": "assert-type",
-      "severity": "error",
-      "stop_column": 30,
-      "stop_line": 139
-    },
     {
       "code": -2,
       "column": 1,
-      "concise_description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA1, type[type[Unknown]]] (trying to access unknown)",
-      "description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA1, type[type[Unknown]]] (trying to access unknown)",
+      "concise_description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA1, type[type]] (trying to access unknown)",
+      "description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA1, type[type]] (trying to access unknown)",
       "line": 143,
       "name": "missing-attribute",
       "severity": "error",
@@ -9986,8 +9953,8 @@
     {
       "code": -2,
       "column": 1,
-      "concise_description": "Class `type` has no class attribute `unknown`",
-      "description": "Class `type` has no class attribute `unknown`",
+      "concise_description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA3, type[type]] (trying to access unknown)",
+      "description": "TODO: Expr::attr_infer_for_type attribute base undefined for type: TypeAlias[TA3, type[type]] (trying to access unknown)",
       "line": 145,
       "name": "missing-attribute",
       "severity": "error",
@@ -10612,8 +10579,8 @@
     {
       "code": -2,
       "column": 7,
-      "concise_description": "Typed dictionary definitions may not specify a metaclass",
-      "description": "Typed dictionary definitions may not specify a metaclass",
+      "concise_description": "Metaclass of `BadTypedDict2` has type `type` that is not a simple class type",
+      "description": "Metaclass of `BadTypedDict2` has type `type` that is not a simple class type",
       "line": 44,
       "name": "invalid-inheritance",
       "severity": "error",

conformance/third_party/conformance.result

@@ -281,13 +281,10 @@
   "specialtypes_promotions.py": [],
   "specialtypes_type.py": [
     "Line 70: Expected 1 errors",
-    "Line 84: Unexpected errors ['assert_type(type, type[Any]) failed']",
-    "Line 99: Unexpected errors ['Object of class `type` has no attribute `unknown`']",
-    "Line 100: Unexpected errors ['Object of class `type` has no attribute `unknown`']",
-    "Line 102: Unexpected errors ['assert_type(Any, tuple[type, ...]) failed']",
-    "Line 106: Unexpected errors ['assert_type(Any, tuple[type, ...]) failed']",
-    "Line 110: Unexpected errors ['assert_type(Any, tuple[type, ...]) failed']",
-    "Line 139: Unexpected errors ['assert_type(type, type[Any]) failed']"
+    "Line 98: Unexpected errors ['assert_type(Any, tuple[type[Any], ...]) failed']",
+    "Line 102: Unexpected errors ['assert_type(Any, tuple[type[Any], ...]) failed']",
+    "Line 106: Unexpected errors ['assert_type(Any, tuple[type[Any], ...]) failed']",
+    "Line 110: Unexpected errors ['assert_type(Any, tuple[type[Any], ...]) failed']"
   ],
   "tuples_type_compat.py": [],
   "tuples_type_form.py": [],

conformance/third_party/results.json

@@ -3,7 +3,7 @@
   "pass": 106,
   "fail": 32,
   "pass_rate": 0.77,
-  "differences": 136,
+  "differences": 133,
   "passing": [
     "aliases_explicit.py",
     "aliases_newtype.py",
@@ -144,7 +144,7 @@
     "qualifiers_annotated.py": 6,
     "qualifiers_final_annotation.py": 7,
     "specialtypes_never.py": 1,
-    "specialtypes_type.py": 8
+    "specialtypes_type.py": 5
   },
   "comment": "@generated"
 }

crates/pyrefly_types/src/display.rs

@@ -708,6 +708,7 @@ impl<'a> TypeDisplayContext<'a> {
                     output.write_str(ta.name.as_str())
                 }
             }
+            Type::Type(box Type::Any(AnyStyle::Implicit)) => output.write_str("type"),
             Type::Type(ty) => {
                 output.write_str("type[")?;
                 self.fmt_helper_generic(ty, false, output)?;

pyrefly/lib/alt/class/class_metadata.rs

@@ -19,6 +19,7 @@ use pyrefly_types::type_var::Restriction;
 use pyrefly_types::typed_dict::ExtraItem;
 use pyrefly_types::typed_dict::ExtraItems;
 use pyrefly_types::typed_dict::TypedDict;
+use pyrefly_types::types::AnyStyle;
 use pyrefly_types::types::Forallable;
 use pyrefly_util::display::DisplayWithCtx;
 use pyrefly_util::prelude::SliceExt;
@@ -914,6 +915,18 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                     }
                 }
             }
+            Type::Type(box Type::Any(AnyStyle::Implicit)) => {
+                // `type[Any]` is canoicalized from `type` or `Type`
+                let type_obj = self.stdlib.builtins_type().class_object();
+                let metadata = self.get_metadata_for_class(type_obj);
+                BaseClassParseResult::Parsed({
+                    ParsedBaseClass {
+                        class_object: type_obj.dupe(),
+                        range,
+                        metadata,
+                    }
+                })
+            }
             _ => {
                 if is_new_type || !ty.is_any() {
                     BaseClassParseResult::InvalidType(ty, range)

pyrefly/lib/alt/expr.rs

@@ -1289,12 +1289,18 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
             Type::ClassDef(cls) => {
                 if cls.is_builtin("tuple") {
                     *ty = Type::type_form(Type::unbounded_tuple(Type::Any(AnyStyle::Implicit)));
+                } else if cls.is_builtin("type") {
+                    // type is equivalent to type[Any]
+                    *ty = Type::type_form(Type::type_form(Type::Any(AnyStyle::Implicit)));
                 } else if cls.has_toplevel_qname("typing", "Any") {
                     *ty = Type::type_form(Type::any_explicit())
                 } else {
                     *ty = Type::type_form(self.promote(cls, range, errors));
                 }
             }
+            Type::ClassType(cls) if cls.is_builtin("type") => {
+                *ty = Type::type_form(Type::Any(AnyStyle::Implicit));
+            }
             _ => {}
         })
     }

pyrefly/lib/alt/types/class_bases.rs

@@ -15,6 +15,7 @@ use pyrefly_python::short_identifier::ShortIdentifier;
 use pyrefly_types::class::ClassType;
 use pyrefly_types::special_form::SpecialForm;
 use pyrefly_types::typed_dict::TypedDict;
+use pyrefly_types::types::AnyStyle;
 use pyrefly_util::display::commas_iter;
 use ruff_python_ast::Expr;
 use ruff_text_size::Ranged;
@@ -299,6 +300,13 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                             }
                         }
                     }
+                    (Type::Type(box Type::Any(AnyStyle::Implicit)), range) => {
+                        // `type` is canonicalized to `Type[Any]`, so we need to handle it here.
+                        let class = self.stdlib.builtins_type().clone();
+                        let bases = self
+                            .get_base_types_for_class(self.stdlib.builtins_type().class_object());
+                        Some((class, bases, range))
+                    }
                     (_, _) => None,
                 }
             })

pyrefly/lib/test/simple.rs

@@ -844,6 +844,19 @@ c2: type[C, C] = C  # E: Expected 1 type argument for `type`, got 2
     "#,
 );
 
+testcase!(
+    test_type_without_argument_is_equivalent_to_type_any,
+    r#"
+from typing import assert_type, Any
+def f(x: type) -> None:
+    g(x)
+    assert_type(x, type[Any])
+def g(x: type[Any]) -> None:
+    f(x)
+    assert_type(x, type)
+"#,
+);
+
 testcase!(
     test_annotated,
     r#"
@@ -1402,7 +1415,7 @@ def g(x: type) -> None: ...
 f(int)
 f(Type)
 f(type)
-f(42)  # E: not assignable to parameter `x` with type `type[Unknown]`
+f(42)  # E: not assignable to parameter `x` with type `type`
 
 g(int)
 g(Type)