refactor(whl_install): remove resolved_unpack_toolchain workaround#905
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UNPACK_TOOLCHAIN is registered in repo.bzl with exec_compatible_with (via the cfg="exec" TOOL_CFGS entry), so ctx.toolchains[UNPACK_TOOLCHAIN] already resolves the exec-platform binary without any indirection. The resolved_unpack_toolchain rule and its cfg="exec" _unpack attr in whl_install were an unnecessary workaround, analogous to resolved_py_toolchain which was removed in #903. Remove resolved_unpack_toolchain from tools.bzl and BUILD.bazel, and replace the ctx.attr._unpack indirection in rule.bzl with a direct toolchain lookup. Add an analysis-time regression test (exec_toolchain_resolution_test) that confirms UNPACK_TOOLCHAIN resolves the exec-platform binary even when the target platform is arm64. The test writes the resolved binary path to a file for both native and arm64-transitioned targets and asserts they are identical, proving exec-platform resolution is honoured throughout platform transitions.
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…macOS failure (#910) ## Problem After #905 removed `resolved_unpack_toolchain`, macOS builds fail when the dependency graph contains a `platform_transition_filegroup` targeting Linux (e.g. OCI crossbuild tests): ``` bazel-out/darwin_arm64-opt-ST-.../bin/py/tools/unpack_bin/unpack: cannot execute binary file ``` The `unpack` binary is ELF (Linux x86-64) instead of Mach-O (darwin-arm64). ## Root cause Bazel analyzes toolchain targets **in the same configuration as the requesting rule**. When a `platform_transition_filegroup` transitions to a Linux target platform, `whl_install` is analyzed in that Linux-targeted configuration. With no `cfg` on the `bin` attribute of `py_tool_toolchain`, the `unpack` binary inherits that Linux target config and is compiled as ELF — which cannot execute on the macOS exec host. `resolved_unpack_toolchain` worked around this by being a regular `dep` with `cfg = "exec"`, explicitly pulling the binary into exec config. The goal of #905 was to remove that workaround, but doing so exposed the underlying issue. ## Fix Introduce two source-toolchain rule variants with explicit `cfg` on their `bin` attribute: - `source_target_py_tool_toolchain` — `cfg = "target"` (venv, shim: target-side tools placed in runfiles) - `source_exec_py_tool_toolchain` — `cfg = "exec"` (unpack: runs on the exec host during the build) `TOOL_CFGS` is already the source of truth for which tools are exec-side (`cfg = "exec"`) vs target-side. The `source_toolchain` macro now looks up the `cfg` from `TOOL_CFGS` by name and selects the appropriate rule variant automatically — no per-call parameter needed. Note: these `source_*` rules are only active when `IS_PRERELEASE = True` (i.e. in this repo during development). Consumers get pre-built binaries via `prebuilt_tool_repo`, which uses `exec_compatible_with` on the `toolchain()` declaration for correct host selection.
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Summary
UNPACK_TOOLCHAINis registered withexec_compatible_with(viacfg="exec"inTOOL_CFGS), soctx.toolchains[UNPACK_TOOLCHAIN]already resolves the exec-platform binary — no indirection needed.resolved_unpack_toolchainrule fromtools.bzlandBUILD.bazel.cfg="exec"_unpackattr +ctx.attr._unpack[ToolchainInfo].bin.binpattern inwhl_install/rule.bzlwith a directctx.toolchains[UNPACK_TOOLCHAIN].bin.binlookup.exec_toolchain_resolution_testto theuv-deps-650/crossbuilde2e case: writes the resolved unpack binary path for both a native target and an arm64-transitioned target, then asserts the paths are identical (proving exec-platform resolution is preserved across target-platform transitions).This is a follow-on cleanup to #903, which removed the analogous
resolved_py_toolchainworkaround.Test plan
exec_toolchain_resolution_testpasses on Linux CI (arm64 and amd64 transitions resolve the same exec-platform binary)resolved_unpack_toolchainremain