Update setuptools-rust and fix building abi3 wheels (#17969)

Newer versions of `setuptools-rust` ignore the `py_limited_api` flag to
`RustExtension`, and instead read it from `bdist_wheel` config.

c.f.
https://github.com/PyO3/setuptools-rust/blob/main/CHANGELOG.md#190-2024-02-24

Author: erikjohnston

build_rust.py

@@ -1,8 +1,10 @@
 # A build script for poetry that adds the rust extension.
 
+import itertools
 import os
 from typing import Any, Dict
 
+from packaging.specifiers import SpecifierSet
 from setuptools_rust import Binding, RustExtension
 
 
@@ -14,10 +16,27 @@ def build(setup_kwargs: Dict[str, Any]) -> None:
         target="synapse.synapse_rust",
         path=cargo_toml_path,
         binding=Binding.PyO3,
+        # This flag is a no-op in the latest versions. Instead, we need to
+        # specify this in the `bdist_wheel` config below.
         py_limited_api=True,
         # We force always building in release mode, as we can't tell the
         # difference between using `poetry` in development vs production.
         debug=False,
     )
     setup_kwargs.setdefault("rust_extensions", []).append(extension)
     setup_kwargs["zip_safe"] = False
+
+    # We lookup the minimum supported python version by looking at
+    # `python_requires` (e.g. ">=3.9.0,<4.0.0") and finding the first python
+    # version that matches. We then convert that into the `py_limited_api` form,
+    # e.g. cp39 for python 3.9.
+    py_limited_api: str
+    python_bounds = SpecifierSet(setup_kwargs["python_requires"])
+    for minor_version in itertools.count(start=8):
+        if f"3.{minor_version}.0" in python_bounds:
+            py_limited_api = f"cp3{minor_version}"
+            break
+
+    setup_kwargs.setdefault("options", {}).setdefault("bdist_wheel", {})[
+        "py_limited_api"
+    ] = py_limited_api

changelog.d/17969.misc

@@ -0,0 +1 @@
+Update setuptools-rust and fix building abi3 wheels in latest version.