Compilation failure under rust nightly webassembly target

[smarter]

Rust Version

• rustc 1.24.0-nightly (dc39c3169 2017-12-17)

Affected Version of clap

• 2.29.0

Rust now has a webassembly target, trying to use it in a project that depends on clap results in a build failure:

     Running `rustc --crate-name clap /home/smarter/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.29.0/src/lib.rs --crate-type lib --emit=dep-info,link -C debuginfo=2 --cfg 'feature="ansi_term"' --cfg 'feature="atty"' --cfg 'feature="color"' --cfg 'feature="default"' --cfg 'feature="strsim"' --cfg 'feature="suggestions"' --cfg 'feature="vec_map"' -C metadata=65f4e6c3f5bc989d -C extra-filename=-65f4e6c3f5bc989d --out-dir /home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps --target wasm32-unknown-unknown -L dependency=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps -L dependency=/home/smarter/opt/rav1e/target/debug/deps --extern unicode_width=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libunicode_width-d8e4ab5b3b6e196a.rlib --extern bitflags=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libbitflags-6b084702002cf111.rlib --extern ansi_term=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libansi_term-ac6664a6dc50e79a.rlib --extern vec_map=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libvec_map-c395abf84ff3b365.rlib --extern textwrap=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libtextwrap-216ed0ff2756cb7b.rlib --extern atty=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libatty-ee3084e679e50df7.rlib --extern strsim=/home/smarter/opt/rav1e/target/wasm32-unknown-unknown/debug/deps/libstrsim-64624fb788d914f4.rlib --cap-lints allow`
error[E0433]: failed to resolve. Could not find `unix` in `os`
   --> /home/smarter/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.29.0/src/app/parser.rs:662:26
    |
662 |             use std::os::unix::ffi::OsStrExt;
    |                          ^^^^ Could not find `unix` in `os`

error[E0433]: failed to resolve. Could not find `unix` in `os`
 --> /home/smarter/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.29.0/src/args/arg.rs:8:14
  |
8 | use std::os::unix::ffi::OsStrExt;
  |              ^^^^ Could not find `unix` in `os`

...

It might be impossible to actually use clap for anything with the wasm backend right now, but it would be nice if it still managed to build.

[kbknapp]

I agree. I haven't really put any thought into wasm because I can't imagine parsing arguments in the browser, but you're right it'd be nice if it still builds.

This would probably be an easy fix, and if anyone wants to add a non-default cargo feature wasm and do the fixes I'd be happy to mentor it.

[rtsao]

I think the clap use case for the wasm target would be consuming it from Node.js. I guess in theory you could build a CLI entirely in Rust then ship it to npm.

[stevepentland]

@kbknapp I'm interested in taking this one on if no one else has started

[kbknapp]

That would be great! Thanks @stevepentland

[stevepentland]

@kbknapp I need to ask about what you meant with a non-default wasm cargo feature? I've been looking through the code at how to reconcile the changes and could use a little insight from you.

[kbknapp]

By non-default I just meant a cargo feature that it's not included in the default features array (and thus opt-in instead of opt-out). However, I now think there are better ways to solve this.

A better solution would be to add some additional OsStrExt traits inside src/osstringext.rs following the OsStrExt3 example for Windows, since Windows is essentially the same problem as wasm.

Actually...now that I think about it, maybe just reusing the OsStrExt3 that Windows uses would work too? That just require changing the cfg statements...hmm I'd try that out first.

So in order of things I'd try:

• Reusing the OsStrExt3 for Windows and wasn't
• Adding a new trait just like OsStrExt3 but for was specifically

[stevepentland]

Alright sounds good, I’ll start there and see how it goes. Thanks!

[kbknapp]

Closed with #1190 thanks to @stevepentland 🎉

[jamesray1]

Getting this error with Drops-of-Diamond/diamond_drops#59 with Clap 2.31.2.