Move setuptools constraint to where --build-option is used

.github/workflows/external-zstd.yml

@@ -25,6 +25,8 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Build
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install --config-settings=--build-option=--system-zstd .
 
@@ -50,5 +52,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Build
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install --config-settings=--build-option=--system-zstd .

.github/workflows/sphinx.yml

@@ -13,6 +13,8 @@ jobs:
         with:
           version: "0.4.29"
       - name: Run Sphinx
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           uv venv --python 3.12 venv
           source venv/bin/activate

.github/workflows/test.yml

@@ -80,6 +80,8 @@ jobs:
       # TODO enable once PyO3 supports 3.13.
       - name: Build (Rust)
         if: matrix.arch == 'x64' && matrix.py != '3.13'
+        env:
+          PIP_CONSTRAINT: 'ci/constraints.txt'
         run: |
           python -m pip install --config-settings='--build-option=--rust-backend' -e .
 

ci/constraints.txt

@@ -0,0 +1,5 @@
+# 69.0.0 breaks handling of --config-settings=--build-option, which our CI
+# relies on. So constrained to an older version until we figure out a
+# workaround. See comment at
+# https://github.com/pypa/pip/issues/11859#issuecomment-2132287974.
+setuptools<69.0.0

pyproject.toml

@@ -29,11 +29,7 @@ Documentation = "https://python-zstandard.readthedocs.io/en/latest/"
 [build-system]
 requires = [
     "cffi>=1.17.0",
-    # 69.0.0 breaks handling of --config-settings=--build-option, which our CI
-    # relies on. So constrained to an older version until we figure out a
-    # workaround. See comment at
-    # https://github.com/pypa/pip/issues/11859#issuecomment-2132287974.
-    "setuptools<69.0.0",
+    "setuptools",
 ]
 # Need to use legacy backend because setup_zstd.py breaks build isolation.
 build-backend = "setuptools.build_meta:__legacy__"