chore(py-315): unblock cp315 wheel builds

.gitlab/package.yml

@@ -18,6 +18,8 @@ variables:
   - "cp312-cp312"
   - "cp313-cp313"
   - "cp314-cp314"
+  # TODO(py-315): enable cp315 once manylinux image supports it
+  # - "cp315-cp315"
 
 .AARCH64_IMAGES: &AARCH64_IMAGES
   - "v85383414-751efc0-manylinux2014_aarch64"
@@ -130,6 +132,21 @@ variables:
         IMAGE_TAG: *AARCH64_IMAGES
         DD_SERVERLESS_BUILD: "1"
 
+# TODO(py-315): fold back into "build linux" once the manylinux image ships
+# a cp315-cp315 interpreter. allow_failure keeps the pipeline green while the
+# upstream pypa/manylinux image is catching up to CPython 3.15.
+"build linux cp315":
+  extends: "build linux"
+  allow_failure: true
+  parallel:
+    matrix:
+      - ARCH_TAG: "amd64"
+        PYTHON_TAG: "cp315-cp315"
+        IMAGE_TAG: *X86_64_IMAGES
+      - ARCH_TAG: "arm64"
+        PYTHON_TAG: "cp315-cp315"
+        IMAGE_TAG: *AARCH64_IMAGES
+
 "build macos":
   extends: .build_base
   tags: [ "macos:sonoma-$ARCH_TAG", "specific:true" ]

setup.py

@@ -122,6 +122,15 @@
 CARGO_TARGET_DIR = NATIVE_CRATE.absolute() / f"target{sys.version_info.major}.{sys.version_info.minor}"
 DD_CARGO_ARGS = shlex.split(os.getenv("DD_CARGO_ARGS", ""))
 
+if sys.version_info >= (3, 15):
+    # TODO(py-315): pyo3-build-config 0.27.x (max Python 3.14) may be resolved by cargo
+    # if the lock file is regenerated without --locked (e.g. in some CI cache scenarios).
+    # Setting PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 tells pyo3-build-config to bypass
+    # the max-version check and build via the stable ABI, which is correct since we
+    # already use py_limited_api="auto" in the RustExtension definition.
+    # pyo3 0.28+ supports Python 3.15 natively, so this is only a safety net.
+    os.environ.setdefault("PYO3_USE_ABI3_FORWARD_COMPATIBILITY", "1")
+
 BUILD_PROFILING_NATIVE_TESTS = os.getenv("DD_PROFILING_NATIVE_TESTS", "0").lower() in ("1", "yes", "on", "true")
 
 CURRENT_OS = platform.system()