0.16.0: wasm32-emscripten fails to build because of default panic handler, recommended workaround?

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Basically:

TL;DR: trying to build for wasm32-emscripten with 0.16.0 currently fails with:

/Users/floh/.zvm/0.16.0/lib/std/Io/Threaded.zig:15315:38: error: expected type 'os.linux.SIG__enum_1199', found 'u32'
        .{ .stopped = posix.W.STOPSIG(status) }
                      ~~~~~~~~~~~~~~~^~~~~~~~
/Users/floh/.zvm/0.16.0/lib/std/os/linux.zig:4036:8: note: enum declared here
} else enum(u32) {

…and:

/Users/floh/.zvm/0.16.0/lib/std/os/emscripten.zig:215:16: error: expected enum, found 'u32'
        return @enumFromInt(EXITSTATUS(s));
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~

@Moka has figured out that the problem can be worked around by overriding the panic handler:

const std = @import("std");
pub const panic = std.debug.FullPanic(wasmPanic);
fn wasmPanic(msg: []const u8, ret_addr: ?usize) noreturn {
    _ = msg; _ = ret_addr;
    @trap();
}

Questions:

  • is this an oversight in the stdlib (e.g. a Zig bug), or expected behaviour?
  • is the above override of the panic handler the recommended workaround, or is there a better way?

…e.g. there is this new --single-threaded cmdline option, can this be used to force the problematic std.Io.Threaded into single-threaded mode (and would that even help)? If yes, how is this used in via build.zig? (haven’t found anything in the std doc page).

Thanks!

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