Add support for abi3.abi3t tag from PEP 803

src/packaging/tags.py

@@ -173,12 +173,21 @@ def _abi3_applies(python_version: PythonVersion, threading: bool) -> bool:
     """
     Determine if the Python version supports abi3.
 
-    PEP 384 was first implemented in Python 3.2. The threaded (`--disable-gil`)
+    PEP 384 was first implemented in Python 3.2. The free-threaded
     builds do not support abi3.
     """
     return len(python_version) > 1 and tuple(python_version) >= (3, 2) and not threading
 
 
+def _abi3t_applies(python_version: PythonVersion, threading: bool) -> bool:
+    """
+    Determine if the Python version supports abi3.abi3t.
+
+    PEP 803 was first implemented in Python 3.15.
+    """
+    return len(python_version) > 1 and tuple(python_version) >= (3, 15) and threading
+
+
 def _cpython_abis(py_version: PythonVersion, warn: bool = False) -> list[str]:
     py_version = tuple(py_version)  # To allow for version comparison.
     abis = []
@@ -256,16 +265,24 @@ def cpython_tags(
 
     threading = _is_threaded_cpython(abis)
     use_abi3 = _abi3_applies(python_version, threading)
+    use_abi3t = _abi3t_applies(python_version, threading)
+
     if use_abi3:
         yield from (Tag(interpreter, "abi3", platform_) for platform_ in platforms)
+    if use_abi3t:
+        yield from (Tag(interpreter, "abi3t", platform_) for platform_ in platforms)
+
     yield from (Tag(interpreter, "none", platform_) for platform_ in platforms)
 
-    if use_abi3:
+    if use_abi3 or use_abi3t:
         for minor_version in range(python_version[1] - 1, 1, -1):
             for platform_ in platforms:
                 version = _version_nodot((python_version[0], minor_version))
                 interpreter = f"cp{version}"
-                yield Tag(interpreter, "abi3", platform_)
+                if use_abi3:
+                    yield Tag(interpreter, "abi3", platform_)
+                if use_abi3t and minor_version > 14:
+                    yield Tag(interpreter, "abi3t", platform_)
 
 
 def _generic_abi() -> list[str]:

tests/test_tags.py

@@ -1042,6 +1042,42 @@ def test_all_args(self) -> None:
             tags.Tag("cp313", "none", "plat2"),
         ]
 
+        result = list(tags.cpython_tags((3, 15), ["cp315t"], ["platform"]))
+        assert result == [
+            tags.Tag("cp315", "cp315t", "platform"),
+            tags.Tag("cp315", "abi3t", "platform"),
+            tags.Tag("cp315", "none", "platform"),
+        ]
+
+        result = list(tags.cpython_tags((3, 16), ["cp316t"], ["platform"]))
+        assert result == [
+            tags.Tag("cp316", "cp316t", "platform"),
+            tags.Tag("cp316", "abi3t", "platform"),
+            tags.Tag("cp316", "none", "platform"),
+            tags.Tag("cp315", "abi3t", "platform"),
+        ]
+
+        result = list(tags.cpython_tags((3, 16), ["cp316"], ["platform"]))
+        assert result == [
+            tags.Tag("cp316", "cp316", "platform"),
+            tags.Tag("cp316", "abi3", "platform"),
+            tags.Tag("cp316", "none", "platform"),
+            tags.Tag("cp315", "abi3", "platform"),
+            tags.Tag("cp314", "abi3", "platform"),
+            tags.Tag("cp313", "abi3", "platform"),
+            tags.Tag("cp312", "abi3", "platform"),
+            tags.Tag("cp311", "abi3", "platform"),
+            tags.Tag("cp310", "abi3", "platform"),
+            tags.Tag("cp39", "abi3", "platform"),
+            tags.Tag("cp38", "abi3", "platform"),
+            tags.Tag("cp37", "abi3", "platform"),
+            tags.Tag("cp36", "abi3", "platform"),
+            tags.Tag("cp35", "abi3", "platform"),
+            tags.Tag("cp34", "abi3", "platform"),
+            tags.Tag("cp33", "abi3", "platform"),
+            tags.Tag("cp32", "abi3", "platform"),
+        ]
+
     def test_python_version_defaults(self) -> None:
         tag = next(tags.cpython_tags(abis=["abi3"], platforms=["any"]))
         interpreter = "cp" + tags._version_nodot(sys.version_info[:2])