Key cffi build-script cache on PYO3_BASE_PYTHON when available#14984
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Key cffi build-script cache on PYO3_BASE_PYTHON when available#14984alex wants to merge 1 commit into
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PEP 517 build isolation creates venvs at random paths and points PYO3_PYTHON at them, so a `rerun-if-env-changed=PYO3_PYTHON` makes the build script re-run on every invocation and defeats caching (see PyO3/pyo3#6113). When PYO3_BASE_PYTHON (the stable underlying interpreter) is present, key the rerun on that instead. A venv cannot change the implementation, version, ABI, or headers of its base interpreter, which is all this script derives -- so the base path is a sound cache key. We still invoke PYO3_PYTHON to locate the binary, since the build venv is where cffi is installed. When PYO3_BASE_PYTHON is absent we fall back to keying on PYO3_PYTHON so manual interpreter switches still trigger a rebuild. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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(Shouldn't land until we depend on a pyo3 release with this) |
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Under PEP 517 build isolation, frontends (pip/uv/build) create venvs at random paths and point
PYO3_PYTHONat them. Becausecryptography-cffi'sbuild.rsdeclarescargo:rerun-if-env-changed=PYO3_PYTHON, that path churn makes the build script re-run on every invocation, defeating build caching. This is the same problem tracked upstream in PyO3/pyo3#6113, which proposes a stablePYO3_BASE_PYTHON(≈sys._base_executable).This change mirrors the proposed "prefer BASE if present" behavior for this crate's build script: when
PYO3_BASE_PYTHONis set, key the rerun on it; otherwise fall back toPYO3_PYTHON.Why keying on the base interpreter is sound here: a venv cannot change the implementation (CPython/PyPy), version, ABI (free-threaded vs. not), or C headers of its base — and those are the only interpreter-derived inputs this script has. We still invoke
PYO3_PYTHONto locate the binary, sincebuild_openssl.pyneeds cffi, which lives in the build venv rather than the base interpreter. The fallback preserves correct rebuild behavior for manual interpreter switches (e.g. settingPYO3_PYTHONin a dev checkout) whenPYO3_BASE_PYTHONis absent.Note: this is forward-looking — it's harmless until a frontend actually sets
PYO3_BASE_PYTHON, at which point caching improves.🤖 Generated with Claude Code