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[ty] implement TypedDict structural assignment #21467

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Merged
merged 2 commits into from
Nov 20, 2025
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[ty] implement TypedDict structural assignment #21467

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19933ce
[ty] implement `TypedDict` structural assignment
oconnor663 Nov 12, 2025
9a33cdd
test structural assignability for both class-style and legacy typeddicts
oconnor663 Nov 20, 2025
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7 changes: 2 additions & 5 deletions crates/ty_python_semantic/resources/mdtest/assignment/annotations.md
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Original file line number Diff line number Diff line change
Expand Up @@ -482,17 +482,14 @@ class TD2(TypedDict):
x: str

def f(self, dt: dict[str, Any], key: str):
# TODO: This should not error once typed dict assignability is implemented.
# error: [invalid-assignment]
x1: TD = dt.get(key, {})
reveal_type(x1) # revealed: TD
reveal_type(x1) # revealed: Any

x2: TD = dt.get(key, {"x": 0})
reveal_type(x2) # revealed: Any

x3: TD | None = dt.get(key, {})
# TODO: This should reveal `Any` once typed dict assignability is implemented.
reveal_type(x3) # revealed: Any | None
reveal_type(x3) # revealed: Any

x4: TD | None = dt.get(key, {"x": 0})
reveal_type(x4) # revealed: Any
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2 changes: 1 addition & 1 deletion crates/ty_python_semantic/resources/mdtest/diagnostics/same_names.md
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Expand Up @@ -265,7 +265,7 @@ import dict_a
import dict_b

def _(b_person: dict_b.Person):
# TODO should be error: [invalid-assignment] "Object of type `dict_b.Person` is not assignable to `dict_a.Person`"
# error: [invalid-assignment] "Object of type `dict_b.Person` is not assignable to `dict_a.Person`"
person_var: dict_a.Person = b_person
```

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31 changes: 16 additions & 15 deletions ...own_key_for_all_…_(1c685d9d10678263).snap → ...own_key_for_all_…_(8a0f0e8ceccc51b2).snap
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Expand Up @@ -3,7 +3,7 @@ source: crates/ty_test/src/lib.rs
expression: snapshot
---
---
mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Unknown key for all elemens of a union
mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Unknown key for all elements of a union
mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
---

Expand All @@ -16,26 +16,27 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_dia
2 |
3 | class Person(TypedDict):
4 | name: str
5 |
6 | class Animal(TypedDict):
7 | name: str
8 | legs: int
9 |
10 | def _(being: Person | Animal) -> None:
11 | # error: [invalid-key]
5 | phone_number: str
6 |
7 | class Animal(TypedDict):
8 | name: str
9 | legs: int
10 |
11 | def _(being: Person | Animal) -> None:
12 | # error: [invalid-key]
13 | being["surname"] = "unknown"
13 | # error: [invalid-key]
14 | being["surname"] = "unknown"
```

# Diagnostics

```
error[invalid-key]: Unknown key "surname" for TypedDict `Person`
--> src/mdtest_snippet.py:13:5
--> src/mdtest_snippet.py:14:5
|
11 | # error: [invalid-key]
12 | # error: [invalid-key]
13 | being["surname"] = "unknown"
13 | # error: [invalid-key]
14 | being["surname"] = "unknown"
| ----- ^^^^^^^^^ Did you mean "name"?
| |
| TypedDict `Person` in union type `Person | Animal`
Expand All @@ -46,11 +47,11 @@ info: rule `invalid-key` is enabled by default

```
error[invalid-key]: Unknown key "surname" for TypedDict `Animal`
--> src/mdtest_snippet.py:13:5
--> src/mdtest_snippet.py:14:5
|
11 | # error: [invalid-key]
12 | # error: [invalid-key]
13 | being["surname"] = "unknown"
13 | # error: [invalid-key]
14 | being["surname"] = "unknown"
| ----- ^^^^^^^^^ Did you mean "name"?
| |
| TypedDict `Animal` in union type `Person | Animal`
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21 changes: 11 additions & 10 deletions ...gnment_diagnosti…_-_Subscript_assignment…_-_Unknown_key_for_one_…_(b515711c0a451a86).snap
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Expand Up @@ -16,23 +16,24 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_dia
2 |
3 | class Person(TypedDict):
4 | name: str
5 |
6 | class Animal(TypedDict):
7 | name: str
8 | legs: int
9 |
10 | def _(being: Person | Animal) -> None:
11 | being["legs"] = 4 # error: [invalid-key]
5 | phone_number: str
6 |
7 | class Animal(TypedDict):
8 | name: str
9 | legs: int
10 |
11 | def _(being: Person | Animal) -> None:
12 | being["legs"] = 4 # error: [invalid-key]
```

# Diagnostics

```
error[invalid-key]: Unknown key "legs" for TypedDict `Person`
--> src/mdtest_snippet.py:11:5
--> src/mdtest_snippet.py:12:5
|
10 | def _(being: Person | Animal) -> None:
11 | being["legs"] = 4 # error: [invalid-key]
11 | def _(being: Person | Animal) -> None:
12 | being["legs"] = 4 # error: [invalid-key]
| ----- ^^^^^^ Unknown key "legs"
| |
| TypedDict `Person` in union type `Person | Animal`
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4 changes: 3 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
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Expand Up @@ -95,6 +95,7 @@ from typing import TypedDict

class Person(TypedDict):
name: str
phone_number: str
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@oconnor663 oconnor663 Nov 15, 2025

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This test wants to look at the diagnostics we print for TypedDicts in a union, but previously Person was a subtype of Animal, so this PR made the union disappear. Adding phone_number breaks the subtyping relationship, so the union remains.

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@oconnor663 oconnor663 Nov 19, 2025

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Actually if we end up going with "don't generally simplify Unions of TypedDicts", I can put this test back the way it was.

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@AlexWaygood AlexWaygood Nov 19, 2025

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I think it's better for the test to pass whichever way we go on that, so this change seems good to me :-)

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@carljm carljm Nov 19, 2025

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Yeah I expect if we land more comprehensive cycle-panic avoidance, we might want to go back to simplifying typed dicts in unions.


class Animal(TypedDict):
name: str
Expand All @@ -104,13 +105,14 @@ def _(being: Person | Animal) -> None:
being["legs"] = 4 # error: [invalid-key]
```

## Unknown key for all elemens of a union
## Unknown key for all elements of a union

```py
from typing import TypedDict

class Person(TypedDict):
name: str
phone_number: str

class Animal(TypedDict):
name: str
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