Unable to use swift_library with a directory

[erikkerber]

When using a directory in the srcs of swift_library, the rules declare an incorrect intermediate object file for the directory and the build fails:

swift_worker: Could not copy bazel-out/darwin_arm64-fastbuild/bin/_swift_incremental/d_objs/c.o to bazel-out/darwin_arm64-fastbuild/bin/d_objs/c.o (No such file or directory)

NOTE: Where the failure happens is less important than there always is a <directory>.o object file declared

This works using objc_library:

Repro (credit @thii)

``` # rule.bzl def _impl(ctx): dir_name = ctx.attr.name out = ctx.actions.declare_directory(dir_name) ctx.actions.run_shell( outputs = [out], command = """ cd {} mkdir {} touch {}/File{} """.format( ctx.bin_dir.path, dir_name, dir_name, ctx.attr.ext, dir_name, ctx.attr.ext, ), ) return [DefaultInfo(files = depset([out]))] my_rule = rule( _impl, attrs = { "ext": attr.string() }, ) ``` ``` # BUILD load(":rule.bzl", "my_rule") load("@build_bazel_rules_swift//swift:swift.bzl", "swift_library") my_rule( name = "a", ext = ".m", ) objc_library( name = "b", srcs = [":a"], ) my_rule( name = "c", ext = ".swift", ) swift_library( name = "d", srcs = [":c"], ) ```

[keith]

A quick hack workaround is to pass --swiftcopt=-wmo --swiftcopt=-num-threads --swiftcopt=0 but this might have other downsides

[keith]

https://github.com/bazelbuild/bazel/issues/21031

[erikkerber]

@keith Think we should close this one as will-never-happen or think there's a maybe-world where this is possible?

[keith]

I'll close as a dup of that one, if that one ever moves we should re-evaluate if we need to make changes

[luispadron]

I'm re-opening because it seems like Bazel will not be able to support this within Starlark (analysis time) but if we can move this work to the execution phase to match rules like objc_library which do work with directory artifacts then thats something worth discussing.