Test on Python 3.15, and fix the typing._eval_type call it breaks

.github/workflows/tests.yml

@@ -36,6 +36,24 @@ jobs:
           # GIL disabled; see docs/free-threading.md.
           - "3.14t"
         experimental: [ false ]
+        include:
+          # Python 3.15, which `allow-prereleases` below resolves to the
+          # newest pre-release the runner image publishes -- 3.15.0rc1 at the
+          # time of writing, and 3.15.0 itself once it ships in October 2026,
+          # with no change needed here.
+          #
+          # Advisory (`experimental: true` -> `continue-on-error`) while 3.15
+          # is a pre-release: the suite passes on 3.15.0rc1 today, but rc2 and
+          # the final release are still to come, and a regression in CPython
+          # itself -- or a test dependency that has no 3.15 wheels yet and
+          # fails to build from source -- must not block merges on a version
+          # nothing runs in production.  Move these two entries up into the
+          # `python-version` list above (and delete them from `include`) to
+          # make 3.15 a required check once 3.15.0 final is out.
+          - python-version: "3.15"
+            experimental: true
+          - python-version: "3.15t"
+            experimental: true
 
     steps:
       - uses: actions/checkout@v4
@@ -49,6 +67,13 @@ jobs:
       - uses: "actions/setup-python@v5"
         with:
           python-version: "${{ matrix.python-version }}"
+          # Required for the 3.15 rows: without it the version spec only
+          # matches stable releases and the job fails with "Version 3.15 was
+          # not found in the local cache".  It is safe to set for every row --
+          # it widens `3.X` to `~3.X.0-0`, and a pre-release only wins when no
+          # stable release satisfies the spec, so 3.10-3.14 still resolve to
+          # their newest stable patch.
+          allow-prereleases: true
           cache: "pip"
           cache-dependency-path: |
             requirements-docs.txt

mode/utils/objects.py

@@ -18,7 +18,7 @@
 from contextlib import suppress
 from decimal import Decimal
 from functools import total_ordering
-from inspect import get_annotations
+from inspect import get_annotations, signature
 from pathlib import Path
 from typing import (
     Any,
@@ -34,11 +34,42 @@
 )
 
 try:
-    from typing import _eval_type  # type: ignore
-except ImportError:
+    from typing import _eval_type as _typing_eval_type  # type: ignore
+except ImportError:  # pragma: no cover
+    _typing_eval_type = None
+    _EVAL_TYPE_WANTS_TYPE_PARAMS = False
+else:
+    # `type_params` (the PEP 695 type parameters in scope) was added to
+    # `typing._eval_type` in 3.13, where omitting it only emitted a
+    # DeprecationWarning and defaulted to `()`.  On 3.15 it became a required
+    # positional argument, so calling without it now fails outright with
+    # "TypeError: _eval_type() missing 1 required positional argument:
+    # 'type_params'".
+    #
+    # The signature is inspected once, here at import.  A try/except TypeError
+    # around the call would be wrong: `_eval_type` legitimately raises
+    # TypeError for annotations `typing._type_check` rejects, and `eval_type`
+    # below depends on being able to tell those apart.
+    _EVAL_TYPE_WANTS_TYPE_PARAMS = (
+        "type_params" in signature(_typing_eval_type).parameters
+    )
+
 
-    def _eval_type(t, globalns, localns, recursive_guard=frozenset()):  # type: ignore
+def _eval_type(
+    t: Any,
+    globalns: Optional[dict[str, Any]],
+    localns: Optional[dict[str, Any]],
+) -> Any:
+    # Nothing resolved through here carries PEP 695 type parameters of its
+    # own, so `()` is both what 3.13/3.14 already substituted when the
+    # argument was omitted and what 3.15 requires -- passing it explicitly
+    # keeps behaviour identical across versions, and silences the 3.13/3.14
+    # deprecation warning on the way.
+    if _typing_eval_type is None:  # pragma: no cover
         return t
+    if _EVAL_TYPE_WANTS_TYPE_PARAMS:
+        return _typing_eval_type(t, globalns, localns, ())
+    return _typing_eval_type(t, globalns, localns)
 
 
 def _is_class_var(typ: Any) -> bool:

pyproject.toml

@@ -40,6 +40,7 @@ classifiers = [
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
     "Programming Language :: Python :: Free Threading :: 2 - Beta",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",