Fix argfile length rustc bug (Windows)

[timbess]

Fix rustc bug on windows by symlinking all transitive deps into a linked directory. This only affects windows because rustc uses an environment variable to track all the paths passed as -Ldependency= on that platform and it silently overflows causing "no such crate" errors when compiling rust projects with large transitive dependency trees.

[UebelAndre]

Thanks! This seems reasonable to me but it seems that some test need to be updated in order to land this

(15:02:04) ERROR: C:/b/bk-windows-zh48/bazel/rules-rust-rustlang/test/unit/exports/BUILD.bazel:3:19: Analysis of target '//test/unit/exports:lib_exports_test' failed

Once they're updated I think it's mergable 😄

[timbess]

@UebelAndre Awesome! Yeah I need to come back to this and figure out why those tests fail. It looks like it expects the first action to always be some Rust artifact, but it's finding my symlinks instead? Not totally sure what's going on there.

[UebelAndre]

@UebelAndre Awesome! Yeah I need to come back to this and figure out why those tests fail. It looks like it expects the first action to always be some Rust artifact, but it's finding my symlinks instead? Not totally sure what's going on there.

that's what it looks like, the fix is probably to iterate over all actions and find the Rustc action. Maybe even assert you only found one.