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Build wheels from the generated downstream sdist #1311
Description
Problem
Fromager currently creates the downstream sdist and then builds the wheel from the original mutable source tree. Sdist creation may modify that tree, for example by generating PKG-INFO, so the wheel is not actually built from the downstream sdist that is recorded or published.
Proposed change
Use the downstream sdist as the canonical input for the wheel build:
prepare source → create downstream sdist → unpack exact sdist → build wheel
The wheel build should consume the verified downstream sdist. Add tests confirming that generated files and sdist file selection are preserved during the wheel build.
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LalatenduMohanty commentedon Sep 1, 2026
This happens on every build — the issue is architectural.
The wheel is always built from the original mutable source tree, never from the downstream sdist. In
_build.py,_build_wheel()calls_build_sdist()first, then passes the samewi.sdist_root_dirtowheels.build_wheel(). The sdist artifact is never unpacked and fed into the wheel build.The source tree is also always modified during sdist creation —
ensure_pkg_info()writes a stubPKG-INFOif one doesn't exist, andpep517_build_sdist()can trigger additional backend-specific changes (e.g.,*.egg-info). So the divergence between the published sdist and the wheel's actual input is guaranteed on every build, though the severity varies by package and build backend.