From 02c102da885922906aa57a0468fde909cbbd2ba4 Mon Sep 17 00:00:00 2001
From: David Peter <sharkdp@users.noreply.github.com>
Date: Thu, 20 Nov 2025 12:59:36 +0100
Subject: [PATCH] [ty] Add tests: `types.UnionType` in
 `isinstance`/`issubclass` (#21537)

## Summary

Add some tests documenting the fact that we don't support
`types.UnionType` in `isinstance`/`issubclass` at the moment.
---
 .../resources/mdtest/narrow/isinstance.md     | 27 +++++++++++++++++++
 .../resources/mdtest/narrow/issubclass.md     | 27 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md b/crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md
index a931b2c367..14aab2ff8e 100644
--- a/crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md
+++ b/crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md
@@ -147,6 +147,33 @@ def _(x: int | str | bytes):
         reveal_type(x)  # revealed: (int & Unknown) | (str & Unknown) | (bytes & Unknown)
 ```
 
+## `classinfo` is a `types.UnionType`
+
+Python 3.10 added the ability to use `Union[int, str]` as the second argument to `isinstance()`:
+
+```py
+from typing import Union
+
+IntOrStr = Union[int, str]
+
+reveal_type(IntOrStr)  # revealed: types.UnionType
+
+def _(x: int | str | bytes | memoryview | range):
+    # TODO: no error
+    # error: [invalid-argument-type]
+    if isinstance(x, IntOrStr):
+        # TODO: Should be `int | str`
+        reveal_type(x)  # revealed: int | str | bytes | memoryview[int] | range
+    # TODO: no error
+    # error: [invalid-argument-type]
+    elif isinstance(x, Union[bytes, memoryview]):
+        # TODO: Should be `bytes | memoryview[int]`
+        reveal_type(x)  # revealed: int | str | bytes | memoryview[int] | range
+    else:
+        # TODO: Should be `range`
+        reveal_type(x)  # revealed: int | str | bytes | memoryview[int] | range
+```
+
 ## `classinfo` is a `typing.py` special form
 
 Certain special forms in `typing.py` are aliases to classes elsewhere in the standard library; these
diff --git a/crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md b/crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md
index 8fa1f54963..a95905d42c 100644
--- a/crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md
+++ b/crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md
@@ -200,6 +200,33 @@ def _(x: type[int | str | bytes]):
         reveal_type(x)  # revealed: (type[int] & Unknown) | (type[str] & Unknown) | (type[bytes] & Unknown)
 ```
 
+## `classinfo` is a `types.UnionType`
+
+Python 3.10 added the ability to use `Union[int, str]` as the second argument to `issubclass()`:
+
+```py
+from typing import Union
+
+IntOrStr = Union[int, str]
+
+reveal_type(IntOrStr)  # revealed: types.UnionType
+
+def f(x: type[int | str | bytes | range]):
+    # TODO: No error
+    # error: [invalid-argument-type]
+    if issubclass(x, IntOrStr):
+        # TODO: Should be `type[int] | type[str]`
+        reveal_type(x)  # revealed: type[int] | type[str] | type[bytes] | <class 'range'>
+    # TODO: No error
+    # error: [invalid-argument-type]
+    elif issubclass(x, Union[bytes, memoryview]):
+        # TODO: Should be `type[bytes]`
+        reveal_type(x)  # revealed: type[int] | type[str] | type[bytes] | <class 'range'>
+    else:
+        # TODO: Should be `<class 'range'>`
+        reveal_type(x)  # revealed: type[int] | type[str] | type[bytes] | <class 'range'>
+```
+
 ## Special cases
 
 ### Emit a diagnostic if the first argument is of wrong type