cargo_build_script: propagate cdylib and bin link args#4097
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A build script's cargo::rustc-cdylib-link-arg, cargo::rustc-link-arg-bin and cargo::rustc-link-arg-bins directives were dropped with a warning, so flags like napi-rs's `-undefined dynamic_lookup` never reached the linker. Route them through BuildInfo to the targets cargo applies them to: * rustc-cdylib-link-arg is collected into BuildInfo.cdylib_link_flags and applied to cdylib/dylib crates. Matching cargo, it propagates transitively: a cdylib picks up the cdylib link args of every build script in its transitive dependencies (rust-lang/cargo#9562). * rustc-link-arg-bin[s] is collected into BuildInfo.bin_link_flags and applied only to the owning crate's bin targets. The build-script runner writes each set to its own flag file, added to the relevant rustc action as an --arg-file, so a non-matching crate type never reads it. Fixes bazelbuild#1062.
UebelAndre
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Jun 23, 2026
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Thanks! Can you add a test for somewhere under //cargo/tests/cargo_build_script that confirms the new flags are behaving as expected for binary and library consumers?
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Fixes #1062.
A build script's
cargo::rustc-cdylib-link-arg,cargo::rustc-link-arg-binandcargo::rustc-link-arg-binswere dropped with a warning, so flags like napi-rs's-undefined dynamic_lookupnever reached the linker.Route them through
BuildInfoto the targets cargo applies them to:rustc-cdylib-link-arg→BuildInfo.cdylib_link_flags, applied to cdylib/dylib crates and propagated transitively (matching cargo, Tracking issue forrustc-cdylib-link-argtransitive warning rust-lang/cargo#9562).rustc-link-arg-bin[s]→BuildInfo.bin_link_flags, applied only to the owning crate's bin targets.The build-script runner writes each set to its own flag file, added to the rustc action as an
--arg-file, so a non-matching crate type never reads it.