From 535b25b0226300d654d687691dca5ab4c982a8e3 Mon Sep 17 00:00:00 2001
From: James Hilliard <james.hilliard1@gmail.com>
Date: Wed, 21 Oct 2026 12:14:28 -0600
Subject: [PATCH] Honor SETUPTOOLS_EXT_SUFFIX for limited-API builds

---
 CHANGELOG.md             |  3 +++
 setuptools_rust/build.py |  4 +++-
 tests/test_build.py      | 40 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 901972e6..73c4fae6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,9 @@
 # Changelog
 
 ## Unreleased
+### Fixed
+- Honor `SETUPTOOLS_EXT_SUFFIX` when replacing extension suffixes for limited-API builds.
+
 ### Packaging
 - Drop support for Python 3.9.
 - Bump `setuptools` minimum version to 83.0.
diff --git a/setuptools_rust/build.py b/setuptools_rust/build.py
index 0cbf64ca..7f839dd4 100644
--- a/setuptools_rust/build.py
+++ b/setuptools_rust/build.py
@@ -491,7 +491,9 @@ def get_dylib_ext_path(self, ext: RustExtension, target_fname: str) -> str:
         if _is_py_limited_api(ext.py_limited_api, self._py_limited_api()):
             abi3_suffix = get_abi3_suffix()
             if abi3_suffix is not None:
-                so_ext = get_config_var("EXT_SUFFIX")
+                so_ext = os.getenv("SETUPTOOLS_EXT_SUFFIX") or get_config_var(
+                    "EXT_SUFFIX"
+                )
                 assert isinstance(so_ext, str)
                 ext_path = ext_path[: -len(so_ext)] + get_abi3_suffix()
 
diff --git a/tests/test_build.py b/tests/test_build.py
index 49d831b1..10265b98 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -1,7 +1,13 @@
+import sysconfig
+from pathlib import Path
 from unittest import mock
 
+import pytest
+from setuptools import Distribution
+
 from setuptools_rust._utils import Env
-from setuptools_rust.build import _override_cargo_default_target
+from setuptools_rust.build import _override_cargo_default_target, build_rust
+from setuptools_rust.extension import RustExtension
 
 NO_ENV = Env(None)
 
@@ -35,3 +41,35 @@ def test_adjusted_local_rust_target_macos():
         assert (
             _override_cargo_default_target("macosx-", NO_ENV) == "x86_64-apple-darwin"
         )
+
+
+@pytest.mark.parametrize(
+    "ext_suffix",
+    [None, "", ".so", ".custom.so", ".custom.extension.suffix.longer.than.default.so"],
+)
+@pytest.mark.parametrize(
+    "abi3_suffix",
+    [
+        None,
+        ".abi3.so",
+        ".abi3-aarch64-linux-gnu.so",
+        ".abi3t-aarch64-linux-gnu.so",
+        ".pyd",
+    ],
+)
+def test_get_dylib_ext_path_suffix_override(monkeypatch, ext_suffix, abi3_suffix):
+    if ext_suffix is None:
+        monkeypatch.delenv("SETUPTOOLS_EXT_SUFFIX", raising=False)
+    else:
+        monkeypatch.setenv("SETUPTOOLS_EXT_SUFFIX", ext_suffix)
+    ext = RustExtension("package.rust")
+    command = build_rust(Distribution())
+    command.plat_name = sysconfig.get_platform()
+    build_ext = command.get_finalized_command("build_ext")
+    path = Path(build_ext.get_ext_fullpath(ext.name))
+    expected = path.with_name("rust" + abi3_suffix) if abi3_suffix else path
+    with (
+        mock.patch.object(command, "_py_limited_api", return_value="cp39"),
+        mock.patch("setuptools_rust.build.get_abi3_suffix", return_value=abi3_suffix),
+    ):
+        assert Path(command.get_dylib_ext_path(ext, ext.name)) == expected