sys: copy files only if needed

[0x2ec]

The cmake build takes care of creating a build dir somewhere in OUT_DIR, so there shouldn't be any need to copy all the sources by hand. This also fixes a problem where Cargo always rebuilds the -sys crate, because the file copies essentially amount to a "touch" on all the files copied to OUT_DIR.

[0x2ec]

I added some small stylistic changes, only because I like fiddling it 😄 feel free to drop those patches if you don't want them.

[Joylei]

The reason to copy source is that the libplctag was trying to modify source to replace version string while building it, which is not allowed by rust build.
Let me check how it works now.

[0x2ec]

The reason to copy source is that the libplctag was trying to modify source to replace version string while building it, which is not allowed by rust build. Let me check how it works now.

That's... interesting behaviour. I thought cmake would copy sources into its build dir, and any modification would happen there. In any case, with 0d2b4df applied, running cargo b --all --examples I don't see any modified files in the repo.

But I can try to dig a bit more into libplctag's build system to see if I can make sense of it.

[0x2ec]

@Joylei I guess you'd be referring to https://github.com/libplctag/libplctag/blob/release/CMakeLists.txt#L327, right?

CONFIGURE_FILE("${lib_SRC_PATH}/version.h.in" "${lib_SRC_PATH}/version.h" @ONLY)

yeah, removing the file makes it reappear when doing a clean build, I guess that's not good.

[0x2ec]

An alternative could be to pull in something like dircpy and set it up like this:

let source_dir = "libplctag";
// fix publish issue: Build scripts should not modify anything outside of OUT_DIR
let dst_dir = PathBuf::from(env::var("OUT_DIR").unwrap()).join("libplctag");
CopyBuilder::new(source_dir, dst_dir)
    .overwrite_if_newer(true)
    .run()
    .unwrap();

would you prefer that?

The overwrite_if_newer() checks the mtime on the source and destination, and copies only if they differ.

[0x2ec]

I could also just expand the existing functionality to check mtime prior to a copy, and only copy when mtimes differ...

[0x2ec]

jus saw the merge, thanks \o/