Fix a small bug in assignability checking

Summary: Fixes a bug where we didn't take readonly-ness into account. Also fixes a comment that described the assignability relationship backwards. Confusingly, the spec and the conformance tests flip the names they use for the "got" and "want" TypedDicts when describing the relationship (i.e., the spec says B is assignable to A if <blah>, whereas the conformance tests say A is assignable to B if <blah>), which may be why we got this wrong.

Reviewed By: samwgoldman

Differential Revision: D78776806

fbshipit-source-id: 12345d101adbbc57979acb4aa455a35973697471

Author: rchen152

conformance/third_party/conformance.exp

@@ -10087,16 +10087,6 @@
       "stop_column": 15,
       "stop_line": 40
     },
-    {
-      "code": -2,
-      "column": 14,
-      "concise_description": "`TypedDict[C2]` is not assignable to `TypedDict[A2]`",
-      "description": "`TypedDict[C2]` is not assignable to `TypedDict[A2]`",
-      "line": 79,
-      "name": "bad-assignment",
-      "stop_column": 15,
-      "stop_line": 79
-    },
     {
       "code": -2,
       "column": 14,

conformance/third_party/conformance.result

@@ -470,9 +470,7 @@
   ],
   "typeddicts_operations.py": [],
   "typeddicts_readonly.py": [],
-  "typeddicts_readonly_consistency.py": [
-    "Line 79: Unexpected errors ['`TypedDict[C2]` is not assignable to `TypedDict[A2]`']"
-  ],
+  "typeddicts_readonly_consistency.py": [],
   "typeddicts_readonly_inheritance.py": [
     "Line 98: Expected 1 errors",
     "Line 106: Expected 1 errors",

conformance/third_party/results.json

@@ -1,9 +1,9 @@
 {
   "total": 136,
-  "pass": 71,
-  "fail": 65,
-  "pass_rate": 0.52,
-  "differences": 288,
+  "pass": 72,
+  "fail": 64,
+  "pass_rate": 0.53,
+  "differences": 287,
   "passing": [
     "aliases_explicit.py",
     "aliases_newtype.py",
@@ -73,6 +73,7 @@
     "typeddicts_final.py",
     "typeddicts_operations.py",
     "typeddicts_readonly.py",
+    "typeddicts_readonly_consistency.py",
     "typeddicts_readonly_kwargs.py",
     "typeddicts_readonly_update.py",
     "typeddicts_usage.py"
@@ -139,7 +140,6 @@
     "tuples_type_compat.py": 2,
     "typeddicts_class_syntax.py": 4,
     "typeddicts_inheritance.py": 1,
-    "typeddicts_readonly_consistency.py": 1,
     "typeddicts_readonly_inheritance.py": 4,
     "typeddicts_required.py": 2,
     "typeddicts_type_consistency.py": 1

pyrefly/lib/solver/subset.rs

@@ -740,8 +740,8 @@ impl<'a, Ans: LookupAnswer> Subset<'a, Ans> {
             (Type::TypedDict(got), Type::TypedDict(want)) => {
                 // For each key in `want`, `got` has the corresponding key
                 // and the corresponding value type in `got` is consistent with the value type in `want`.
-                // For each required key in `got`, the corresponding key is required in `want`.
-                // For each non-required key in `got`, the corresponding key is not required in `want`.
+                // For each required key in `want`, the corresponding key is required in `got`.
+                // For each non-required, non-readonly key in `want`, the corresponding key is not required in `got`.
                 let got_fields = self.type_order.typed_dict_fields(got);
                 let want_fields = self.type_order.typed_dict_fields(want);
 
@@ -757,9 +757,13 @@ impl<'a, Ans: LookupAnswer> Subset<'a, Ans> {
                         }
                     })
                 }) && got_fields.iter().all(|(k, got_v)| {
-                    want_fields
-                        .get(k)
-                        .is_none_or(|want_v| got_v.required == want_v.required)
+                    want_fields.get(k).is_none_or(|want_v| {
+                        if want_v.required {
+                            got_v.required
+                        } else {
+                            want_v.is_read_only() || !got_v.required
+                        }
+                    })
                 })
             }
             (Type::TypedDict(got), Type::PartialTypedDict(want)) => {

pyrefly/lib/test/typed_dict.rs

@@ -1003,3 +1003,16 @@ class TD3(TypedDict, bar="test", baz=False):  # E: TypedDict does not support ke
     x: int
 "#,
 );
+
+testcase!(
+    test_nonrequired_readonly,
+    r#"
+from typing import NotRequired, ReadOnly, Required, TypedDict
+class A(TypedDict):
+    x: NotRequired[ReadOnly[str]]
+class B(TypedDict):
+    x: Required[str]
+b: B = {'x': ''}
+a: A = b
+    "#,
+);