promote anonymous typed dicts when unioning (#2351)

Summary: Pull Request resolved: #2351

Differential Revision: D92586637

Author: yangdanny97

crates/pyrefly_types/src/simplify.rs

@@ -13,6 +13,7 @@ use crate::class::ClassType;
 use crate::literal::Lit;
 use crate::stdlib::Stdlib;
 use crate::tuple::Tuple;
+use crate::typed_dict::TypedDict;
 use crate::types::Type;
 use crate::types::Union;
 
@@ -74,6 +75,7 @@ fn unions_internal(
         let mut res = flatten_and_dedup(xs);
         if let Some(stdlib) = stdlib {
             collapse_literals(&mut res, stdlib, enum_members.unwrap_or(&|_| None));
+            promote_anonymous_typed_dicts(&mut res, stdlib);
         }
         collapse_tuple_unions_with_empty(&mut res);
         // `res` is collapsible again if `flatten_and_dedup` drops `xs` to 0 or 1 elements
@@ -254,6 +256,17 @@ fn collapse_literals(
     }
 }
 
+/// Promote anonymous typed dicts to `dict[str, value_type]`
+fn promote_anonymous_typed_dicts(types: &mut [Type], stdlib: &Stdlib) {
+    for ty in types.iter_mut() {
+        if let Type::TypedDict(TypedDict::Anonymous(inner)) = ty {
+            *ty = stdlib
+                .dict(stdlib.str().clone().to_type(), inner.value_type.clone())
+                .to_type();
+        }
+    }
+}
+
 fn collapse_tuple_unions_with_empty(types: &mut Vec<Type>) {
     let Some(empty_idx) = types.iter().position(|t| match t {
         Type::Tuple(Tuple::Concrete(elts)) => elts.is_empty(),

pyrefly/lib/test/attributes.rs

@@ -2284,7 +2284,8 @@ class A:
         self.y = {"x": 0} if check else 42
 def f(a: A):
     x: TD = a.x
-    y: TD | int = a.y
+    # anoynmous typed dicts are promoted away when unioned
+    y: dict[str, int] | int = a.y
     "#,
 );
 

pyrefly/lib/test/dict.rs

@@ -14,6 +14,21 @@ dict(x = 1, y = "test")
     "#,
 );
 
+testcase!(
+    test_anonymous_typed_dict_union_promotion,
+    r#"
+from typing import assert_type
+
+def test(cond: bool):
+    x = {"a": 1, "b": "2"}
+    y = {"a": 1, "b": "2", "c": 3}
+    # we promote anonymous typed dicts when unioning
+    z = x if cond else y
+    assert_type(z["a"], int | str)
+    assert_type(z, dict[str, int | str])
+"#,
+);
+
 testcase!(
     test_unpack_empty,
     r#"
@@ -48,6 +63,6 @@ def bar(yes: bool) -> None:
     else:
         kwargs = {"goodbye": 1}
 
-    foo(**kwargs)  
+    foo(**kwargs)
 "#,
 );