[ty] dict is not assignable to TypedDict (#21238)

## Summary

A lot of the bidirectional inference work relies on `dict` not being
assignable to `TypedDict`, so I think it makes sense to add this before
fully implementing astral-sh/ty#1387.

Author: ibraheemdev

crates/ty_python_semantic/resources/mdtest/bidirectional.md

@@ -76,6 +76,7 @@ def _() -> TD:
 
 def _() -> TD:
     # error: [missing-typed-dict-key] "Missing required key 'x' in TypedDict `TD` constructor"
+    # error: [invalid-return-type]
     return {}
 ```
 

crates/ty_python_semantic/resources/mdtest/call/overloads.md

@@ -1685,8 +1685,7 @@ def int_or_str() -> int | str:
 x = f([{"x": 1}], int_or_str())
 reveal_type(x)  # revealed: int | str
 
-# TODO: error: [no-matching-overload] "No overload of function `f` matches arguments"
-# we currently incorrectly consider `list[dict[str, int]]` a subtype of `list[T]`
+# error: [no-matching-overload] "No overload of function `f` matches arguments"
 f([{"y": 1}], int_or_str())
 ```
 

crates/ty_python_semantic/resources/mdtest/call/union.md

@@ -277,7 +277,6 @@ def _(flag: bool):
     x = f({"x": 1})
     reveal_type(x)  # revealed: int
 
-    # TODO: error: [invalid-argument-type] "Argument to function `f` is incorrect: Expected `T`, found `dict[str, int]`"
-    # we currently consider `TypedDict` instances to be subtypes of `dict`
+    # error: [invalid-argument-type] "Argument to function `f` is incorrect: Expected `T`, found `dict[Unknown | str, Unknown | int]`"
     f({"y": 1})
 ```

crates/ty_python_semantic/resources/mdtest/comprehensions/basic.md

@@ -162,10 +162,13 @@ The type context is propagated down into the comprehension:
 class Person(TypedDict):
     name: str
 
+# TODO: This should not error.
+# error: [invalid-assignment]
 persons: list[Person] = [{"name": n} for n in ["Alice", "Bob"]]
 reveal_type(persons)  # revealed: list[Person]
 
-# TODO: This should be an error
+# TODO: This should be an invalid-key error.
+# error: [invalid-assignment]
 invalid: list[Person] = [{"misspelled": n} for n in ["Alice", "Bob"]]
 ```
 

crates/ty_python_semantic/resources/mdtest/snapshots/typed_dict.md_-_`TypedDict`_-_Diagnostics_(e5289abf5c570c29).snap

@@ -39,16 +39,19 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/typed_dict.md
 25 |     person[str_key] = "Alice"  # error: [invalid-key]
 26 | 
 27 | def create_with_invalid_string_key():
-28 |     alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}  # error: [invalid-key]
-29 |     bob = Person(name="Bob", age=25, unknown="Bar")  # error: [invalid-key]
-30 | from typing_extensions import ReadOnly
-31 | 
-32 | class Employee(TypedDict):
-33 |     id: ReadOnly[int]
-34 |     name: str
-35 | 
-36 | def write_to_readonly_key(employee: Employee):
-37 |     employee["id"] = 42  # error: [invalid-assignment]
+28 |     # error: [invalid-key]
+29 |     alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}
+30 | 
+31 |     # error: [invalid-key]
+32 |     bob = Person(name="Bob", age=25, unknown="Bar")
+33 | from typing_extensions import ReadOnly
+34 | 
+35 | class Employee(TypedDict):
+36 |     id: ReadOnly[int]
+37 |     name: str
+38 | 
+39 | def write_to_readonly_key(employee: Employee):
+40 |     employee["id"] = 42  # error: [invalid-assignment]
 ```
 
 # Diagnostics
@@ -158,52 +161,52 @@ info: rule `invalid-key` is enabled by default
 
 ```
 error[invalid-key]: Invalid key for TypedDict `Person`
-  --> src/mdtest_snippet.py:28:21
+  --> src/mdtest_snippet.py:29:21
    |
 27 | def create_with_invalid_string_key():
-28 |     alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}  # error: [invalid-key]
+28 |     # error: [invalid-key]
+29 |     alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}
    |                     -----------------------------^^^^^^^^^--------
    |                     |                            |
    |                     |                            Unknown key "unknown"
    |                     TypedDict `Person`
-29 |     bob = Person(name="Bob", age=25, unknown="Bar")  # error: [invalid-key]
-30 | from typing_extensions import ReadOnly
+30 |
+31 |     # error: [invalid-key]
    |
 info: rule `invalid-key` is enabled by default
 
 ```
 
 ```
 error[invalid-key]: Invalid key for TypedDict `Person`
-  --> src/mdtest_snippet.py:29:11
+  --> src/mdtest_snippet.py:32:11
    |
-27 | def create_with_invalid_string_key():
-28 |     alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}  # error: [invalid-key]
-29 |     bob = Person(name="Bob", age=25, unknown="Bar")  # error: [invalid-key]
+31 |     # error: [invalid-key]
+32 |     bob = Person(name="Bob", age=25, unknown="Bar")
    |           ------ TypedDict `Person`  ^^^^^^^^^^^^^ Unknown key "unknown"
-30 | from typing_extensions import ReadOnly
+33 | from typing_extensions import ReadOnly
    |
 info: rule `invalid-key` is enabled by default
 
 ```
 
 ```
 error[invalid-assignment]: Cannot assign to key "id" on TypedDict `Employee`
-  --> src/mdtest_snippet.py:37:5
+  --> src/mdtest_snippet.py:40:5
    |
-36 | def write_to_readonly_key(employee: Employee):
-37 |     employee["id"] = 42  # error: [invalid-assignment]
+39 | def write_to_readonly_key(employee: Employee):
+40 |     employee["id"] = 42  # error: [invalid-assignment]
    |     -------- ^^^^ key is marked read-only
    |     |
    |     TypedDict `Employee`
    |
 info: Item declaration
-  --> src/mdtest_snippet.py:33:5
+  --> src/mdtest_snippet.py:36:5
    |
-32 | class Employee(TypedDict):
-33 |     id: ReadOnly[int]
+35 | class Employee(TypedDict):
+36 |     id: ReadOnly[int]
    |     ----------------- Read-only item declared here
-34 |     name: str
+37 |     name: str
    |
 info: rule `invalid-assignment` is enabled by default
 

crates/ty_python_semantic/resources/mdtest/typed_dict.md

@@ -96,29 +96,29 @@ The construction of a `TypedDict` is checked for type correctness:
 ```py
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`"
 eve1a: Person = {"name": b"Eve", "age": None}
+
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`"
 eve1b = Person(name=b"Eve", age=None)
 
-# TODO should reveal Person (should be fixed by implementing assignability for TypedDicts)
-reveal_type(eve1a)  # revealed: dict[Unknown | str, Unknown | bytes | None]
+reveal_type(eve1a)  # revealed: Person
 reveal_type(eve1b)  # revealed: Person
 
 # error: [missing-typed-dict-key] "Missing required key 'name' in TypedDict `Person` constructor"
 eve2a: Person = {"age": 22}
+
 # error: [missing-typed-dict-key] "Missing required key 'name' in TypedDict `Person` constructor"
 eve2b = Person(age=22)
 
-# TODO should reveal Person (should be fixed by implementing assignability for TypedDicts)
-reveal_type(eve2a)  # revealed: dict[Unknown | str, Unknown | int]
+reveal_type(eve2a)  # revealed: Person
 reveal_type(eve2b)  # revealed: Person
 
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 eve3a: Person = {"name": "Eve", "age": 25, "extra": True}
+
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 eve3b = Person(name="Eve", age=25, extra=True)
 
-# TODO should reveal Person (should be fixed by implementing assignability for TypedDicts)
-reveal_type(eve3a)  # revealed: dict[Unknown | str, Unknown | str | int]
+reveal_type(eve3a)  # revealed: Person
 reveal_type(eve3b)  # revealed: Person
 ```
 
@@ -238,15 +238,19 @@ All of these are missing the required `age` field:
 ```py
 # error: [missing-typed-dict-key] "Missing required key 'age' in TypedDict `Person` constructor"
 alice2: Person = {"name": "Alice"}
+
 # error: [missing-typed-dict-key] "Missing required key 'age' in TypedDict `Person` constructor"
 Person(name="Alice")
+
 # error: [missing-typed-dict-key] "Missing required key 'age' in TypedDict `Person` constructor"
 Person({"name": "Alice"})
 
 # error: [missing-typed-dict-key] "Missing required key 'age' in TypedDict `Person` constructor"
+# error: [invalid-argument-type]
 accepts_person({"name": "Alice"})
 
-# TODO: this should be an error, similar to the above
+# TODO: this should be an invalid-key error, similar to the above
+# error: [invalid-assignment]
 house.owner = {"name": "Alice"}
 
 a_person: Person
@@ -259,19 +263,25 @@ All of these have an invalid type for the `name` field:
 ```py
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
 alice3: Person = {"name": None, "age": 30}
+
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
 Person(name=None, age=30)
+
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
 Person({"name": None, "age": 30})
 
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
+# error: [invalid-argument-type]
 accepts_person({"name": None, "age": 30})
-# TODO: this should be an error, similar to the above
+
+# TODO: this should be an invalid-key error
+# error: [invalid-assignment]
 house.owner = {"name": None, "age": 30}
 
 a_person: Person
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
 a_person = {"name": None, "age": 30}
+
 # error: [invalid-argument-type] "Invalid argument to key "name" with declared type `str` on TypedDict `Person`: value of type `None`"
 (a_person := {"name": None, "age": 30})
 ```
@@ -281,19 +291,25 @@ All of these have an extra field that is not defined in the `TypedDict`:
 ```py
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 alice4: Person = {"name": "Alice", "age": 30, "extra": True}
+
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 Person(name="Alice", age=30, extra=True)
+
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 Person({"name": "Alice", "age": 30, "extra": True})
 
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
+# error: [invalid-argument-type]
 accepts_person({"name": "Alice", "age": 30, "extra": True})
-# TODO: this should be an error
+
+# TODO: this should be an invalid-key error
+# error: [invalid-assignment]
 house.owner = {"name": "Alice", "age": 30, "extra": True}
 
 a_person: Person
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 a_person = {"name": "Alice", "age": 30, "extra": True}
+
 # error: [invalid-key] "Invalid key for TypedDict `Person`: Unknown key "extra""
 (a_person := {"name": "Alice", "age": 30, "extra": True})
 ```
@@ -490,6 +506,15 @@ dangerous(alice)
 reveal_type(alice["name"])  # revealed: str
 ```
 
+Likewise, `dict`s are not assignable to typed dictionaries:
+
+```py
+alice: dict[str, str] = {"name": "Alice"}
+
+# error: [invalid-assignment] "Object of type `dict[str, str]` is not assignable to `Person`"
+alice: Person = alice
+```
+
 ## Key-based access
 
 ### Reading
@@ -977,7 +1002,7 @@ class Person(TypedDict):
     name: str
     age: int | None
 
-# TODO: this should be an error
+# error: [invalid-assignment] "Object of type `MyDict` is not assignable to `Person`"
 x: Person = MyDict({"name": "Alice", "age": 30})
 ```
 
@@ -1029,8 +1054,11 @@ def write_to_non_literal_string_key(person: Person, str_key: str):
     person[str_key] = "Alice"  # error: [invalid-key]
 
 def create_with_invalid_string_key():
-    alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}  # error: [invalid-key]
-    bob = Person(name="Bob", age=25, unknown="Bar")  # error: [invalid-key]
+    # error: [invalid-key]
+    alice: Person = {"name": "Alice", "age": 30, "unknown": "Foo"}
+
+    # error: [invalid-key]
+    bob = Person(name="Bob", age=25, unknown="Bar")
 ```
 
 Assignment to `ReadOnly` keys:

crates/ty_python_semantic/src/types.rs

@@ -1987,11 +1987,14 @@ impl<'db> Type<'db> {
                 ConstraintSet::from(false)
             }
 
-            (Type::TypedDict(_), _) | (_, Type::TypedDict(_)) => {
+            (Type::TypedDict(_), _) => {
                 // TODO: Implement assignability and subtyping for TypedDict
                 ConstraintSet::from(relation.is_assignability())
             }
 
+            // A non-`TypedDict` cannot subtype a `TypedDict`
+            (_, Type::TypedDict(_)) => ConstraintSet::from(false),
+
             // Note that the definition of `Type::AlwaysFalsy` depends on the return value of `__bool__`.
             // If `__bool__` always returns True or False, it can be treated as a subtype of `AlwaysTruthy` or `AlwaysFalsy`, respectively.
             (left, Type::AlwaysFalsy) => ConstraintSet::from(left.bool(db).is_always_false()),

crates/ty_python_semantic/src/types/call/bind.rs

@@ -3582,6 +3582,11 @@ impl<'db> BindingError<'db> {
                 expected_ty,
                 provided_ty,
             } => {
+                // TODO: Ideally we would not emit diagnostics for `TypedDict` literal arguments
+                // here (see `diagnostic::is_invalid_typed_dict_literal`). However, we may have
+                // silenced diagnostics during overload evaluation, and rely on the assignability
+                // diagnostic being emitted here.
+
                 let range = Self::get_node(node, *argument_index);
                 let Some(builder) = context.report_lint(&INVALID_ARGUMENT_TYPE, range) else {
                     return;

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -2003,6 +2003,20 @@ pub(super) fn report_slice_step_size_zero(context: &InferContext, node: AnyNodeR
     builder.into_diagnostic("Slice step size cannot be zero");
 }
 
+// We avoid emitting invalid assignment diagnostic for literal assignments to a `TypedDict`, as
+// they can only occur if we already failed to validate the dict (and emitted some diagnostic).
+pub(crate) fn is_invalid_typed_dict_literal(
+    db: &dyn Db,
+    target_ty: Type,
+    source: AnyNodeRef<'_>,
+) -> bool {
+    target_ty
+        .filter_union(db, Type::is_typed_dict)
+        .as_typed_dict()
+        .is_some()
+        && matches!(source, AnyNodeRef::ExprDict(_))
+}
+
 fn report_invalid_assignment_with_message(
     context: &InferContext,
     node: AnyNodeRef,
@@ -2040,15 +2054,27 @@ pub(super) fn report_invalid_assignment<'db>(
     target_ty: Type,
     mut source_ty: Type<'db>,
 ) {
+    let value_expr = match definition.kind(context.db()) {
+        DefinitionKind::Assignment(def) => Some(def.value(context.module())),
+        DefinitionKind::AnnotatedAssignment(def) => def.value(context.module()),
+        DefinitionKind::NamedExpression(def) => Some(&*def.node(context.module()).value),
+        _ => None,
+    };
+
+    if let Some(value_expr) = value_expr
+        && is_invalid_typed_dict_literal(context.db(), target_ty, value_expr.into())
+    {
+        return;
+    }
+
     let settings =
         DisplaySettings::from_possibly_ambiguous_type_pair(context.db(), target_ty, source_ty);
 
-    if let DefinitionKind::AnnotatedAssignment(annotated_assignment) = definition.kind(context.db())
-        && let Some(value) = annotated_assignment.value(context.module())
-    {
+    if let Some(value_expr) = value_expr {
         // Re-infer the RHS of the annotated assignment, ignoring the type context for more precise
         // error messages.
-        source_ty = infer_isolated_expression(context.db(), definition.scope(context.db()), value);
+        source_ty =
+            infer_isolated_expression(context.db(), definition.scope(context.db()), value_expr);
     }
 
     report_invalid_assignment_with_message(
@@ -2070,6 +2096,11 @@ pub(super) fn report_invalid_attribute_assignment(
     source_ty: Type,
     attribute_name: &'_ str,
 ) {
+    // TODO: Ideally we would not emit diagnostics for `TypedDict` literal arguments
+    // here (see `diagnostic::is_invalid_typed_dict_literal`). However, we may have
+    // silenced diagnostics during attribute resolution, and rely on the assignability
+    // diagnostic being emitted here.
+
     report_invalid_assignment_with_message(
         context,
         node,