aspect-build
feat(pex): support cross builds of py_pex_binary targetting Linux
Cross builds of bundled applications would be really nice to be able to do. Often, we're bundling for the purposes of distributing an artifact, and in many cases the ultimate execution targets for the distributed artifact do not necessarily match the build machine.
The PyPex action itself can support cross-builds in a fairly straightforward way:
use the cfg="exec" Python to run the PEX bundling code, rather than the
cfg="target" Python. The former is what this ruleset's PEX wrapper is already
running as, so all the must be done is to not request an alternative interpreter
when calling into the PEX library. Unfortunately, that's precisely what the tool
had been doing.
For instance, prior to this change, building an x86-64 Linux PEX binary on Macos resulted in failures with diagnostics of the form:
pex.executor.Executor.ExecutionError: OSError(8, 'Exec format error') while trying to execute `['/private/var/tmp/_bazel_peter/0576637e8cc9ee3ad4c778fd98f4cba7/external/python_toolchain_x86_64-unknown-linux-gnu/bin/python3.9', [...]
The way rules_py is using PEX, changing the interpreter should not have other
meaningful effects. Perhaps if we were
allowing PEX to resolve requirements freely, changing the interpreter would change
the resolution results. However, that's non-hermetic, and the rules_py PEX wrapper
already explicitly controls what dependencies are used and where they come from.
Unfortunately, we are only able to support cross-builds targetting Linux at the current time (and perhaps MacOS in release rulesets). Other accidental complexity blocks targetting of other platforms. See https://github.com/aspect-build/rules_py/issues/625 for details. However, even limited to just Linux as a cross target, the feature is valuable as Linux is very popular in certain contexts.
Changes are visible to end-users: yes
- Searched for relevant documentation and updated as needed: yes
- Breaking change (forces users to change their own code or config): no
- Suggested release notes appear below: no
Test plan
- Covered by existing test cases
- New test cases added
