Emscripten target broken on win32 with 1.20.0 release

[vvanders]

It looks like the recent change in how Command executes batch files(see rust-lang/cc-rs#239 for details) has also caused the emscripten target to regress and fail to compile on win32.

I'm also seeing the libc::c_char type change from *const i8 to *const u8 which is causing problems with a bunch of C bindings I have.

Below example works fine when I switch back to 1.19.0.

I tried this code:
https://github.com/vvanders/rust_command_repro

I expected to see this happen: Successful compile

Instead, this happened:

C:\dev\command_repro>cargo build --release --target=asmjs-unknown-emscripten
   Compiling command_repro v0.1.0 (file:///C:/dev/command_repro)
error: linking with `emcc.bat` failed: exit code: 2
  |
  = note: "emcc.bat" "-s" "DISABLE_EXCEPTION_CATCHING=0" "-L" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib" "C:\\dev\\command_repro\\target\\asmjs-unknown-emscripten\\release\\deps\\command_repro-0b0fbd0388217b85.0.o" "-o" "C:\\dev\\command_repro\\target\\asmjs-unknown-emscripten\\release\\deps\\command_repro-0b0fbd0388217b85.js" "-s" "EXPORTED_FUNCTIONS=[\"_main\",\"___rdl_shrink_in_place\",\"___rdl_alloc_excess\",\"___rdl_usable_size\",\"___rdl_alloc\",\"___rdl_realloc_excess\",\"___rdl_realloc\",\"___rdl_oom\",\"___rdl_grow_in_place\",\"___rdl_alloc_zeroed\",\"___rdl_dealloc\",\"_rust_eh_personality\"]" "C:\\dev\\command_repro\\target\\asmjs-unknown-emscripten\\release\\deps\\command_repro-0b0fbd0388217b85.crate.allocator.o" "-O3" "--memory-init-file" "0" "-g0" "-s" "DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=[]" "-L" "C:\\dev\\command_repro\\target\\asmjs-unknown-emscripten\\release\\deps" "-L" "C:\\dev\\command_repro\\target\\release\\deps" "-L" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libstd-881b9fdbdf1d515b.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\liballoc_system-3c10208cdd7e61cb.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\librand-32f648f7f7567c6c.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libpanic_unwind-9cbadc6554202be9.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\liballoc-bc70b4efeaeb398c.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libstd_unicode-a0ad42dc8f5856aa.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libunwind-618c266cf9124966.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\liblibc-16f3b02b9a976b94.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libcore-21491ce3d14f1ef2.rlib" "C:\\Users\\valer\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib\\rustlib\\asmjs-unknown-emscripten\\lib\\libcompiler_builtins-b9713bd7f605c0b2.rlib" "-l" "c" "-s" "ERROR_ON_UNDEFINED_SYMBOLS=1"
  = note: python: can't open file 'C:\dev\command_repro\\emcc': [Errno 2] No such file or directory

Meta

rustc --version --verbose:
C:\dev\command_repro>rustc --version --verbose
rustc 1.20.0 (f3d6973 2017-08-27)
binary: rustc
commit-hash: f3d6973
commit-date: 2017-08-27
host: x86_64-pc-windows-msvc
release: 1.20.0
LLVM version: 4.0

[krampenschiesser]

Got the same issue here :(

[alexcrichton]

Thanks for opening this up @vvanders!

Could you test out a possible solution for this? If you use -C linker to override the linker used here, does this program work?

use std::env;
use std::process::{self, Command};

fn main() {
    let status = Command::new("cmd")
        .arg("/c")
        .arg("emcc.bat")
        .args(&env::args().skip(1).collect::<Vec<_>>())
        .status()
        .expect("failed to spawn `cmd`");
    process::exit(status.code().unwrap());
}

My hope is that we just need to do cmd /c emcc.bat rather than emcc.bat, but that'd help confirm the fix!

[vvanders]

Hey @alexcrichton, can you explain down to use -C linker flag in a bit more detail? I'm not totally following the steps you listed out above.

[alexcrichton]

Oh sure yeah, so ideally you could do:

# Compile the program in the comment above
$ rustc foo.rs -o foo.exe

# Compile a "hello world"
$ rustc hello.rs --target asmjs-unknown-emscripten -C linker=./foo.exe

And see if that works?

[vvanders]

Yup, that appears to work. I'll look into the libc changes on the other issue but this should address things on Win32.

[alexcrichton]

Ok excellent! I'll prepare a PR for this

[alexcrichton]

Ok I've opened a PR for this change at #44542

I've also nominated that for beta to make sure we fix this in 1.21

[alexcrichton]

In the meantime I've also tagged this as a stable regression, but it should be fixed by the PR above

[alexcrichton]

Beta backported in #44357