fix the length of platform.uname_result (#13068)

It should be a 6-tuple, once processor is added. This makes sure mypy understands that.

Fixes https://github.com/python/typeshed/issues/13064

stdlib/@tests/test_cases/check_platform.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+import platform
+import sys
+from typing_extensions import assert_type
+
+# platform.uname_result emulates a 6 field named tuple, but on 3.9+ the processor
+# field is lazily evaluated, which results in it being a little funky.
+uname = platform.uname()
+if sys.version_info >= (3, 9):
+    myuname = platform.uname_result("Darwin", "local", "22.5.0", "Darwin Kernel Version 22.5.0", "arm64")
+else:
+    myuname = platform.uname_result("Darwin", "local", "22.5.0", "Darwin Kernel Version 22.5.0", "arm64", "arm")
+
+assert_type(uname, platform.uname_result)
+assert_type(myuname, platform.uname_result)
+
+assert_type(uname[5], str)
+assert_type(myuname[5], str)

stdlib/platform.pyi

@@ -1,5 +1,6 @@
 import sys
 from typing import NamedTuple, type_check_only
+from typing_extensions import Self
 
 def libc_ver(executable: str | None = None, lib: str = "", version: str = "", chunksize: int = 16384) -> tuple[str, str]: ...
 def win32_ver(release: str = "", version: str = "", csd: str = "", ptype: str = "") -> tuple[str, str, str, str]: ...
@@ -15,6 +16,8 @@ def system_alias(system: str, release: str, version: str) -> tuple[str, str, str
 def architecture(executable: str = sys.executable, bits: str = "", linkage: str = "") -> tuple[str, str]: ...
 
 if sys.version_info >= (3, 9):
+    # This class is not exposed. It calls itself platform.uname_result_base.
+    # At runtime it only has 5 fields.
     @type_check_only
     class _uname_result_base(NamedTuple):
         system: str
@@ -22,12 +25,23 @@ if sys.version_info >= (3, 9):
         release: str
         version: str
         machine: str
+        # This base class doesn't have this field at runtime, but claiming it
+        # does is the least bad way to handle the situation. Nobody really
+        # sees this class anyway. See #13068
+        processor: str
 
+    # uname_result emulates a 6-field named tuple, but the processor field
+    # is lazily evaluated rather than being passed in to the constructor.
     class uname_result(_uname_result_base):
+        if sys.version_info >= (3, 10):
+            __match_args__ = ("system", "node", "release", "version", "machine")  # pyright: ignore[reportAssignmentType]
+
+        def __new__(_cls, system: str, node: str, release: str, version: str, machine: str) -> Self: ...
         @property
         def processor(self) -> str: ...
 
 else:
+    # On 3.8, uname_result is actually just a regular NamedTuple.
     class uname_result(NamedTuple):
         system: str
         node: str