WASM compilation broken on nightly?

[jD91mZM2]

A thing works fine when compiled with stable rust, but fails at runtime with nightly.

I tried this code:
https://github.com/jD91mZM2/jD91mZM2.github.io

I expected this to happen:
It'd compile and work, just like it used to.

Instead, this happened:

wasm validation error: at offset 1121: type mismatch: expression has type i32 but expected f64

It appears it has to do something with

extern {
    fn alert(string: *mut u16);
    fn log(string: *mut u16);
}

Specifically, changing them to take f64 instead fails with:

wasm validation error: at offset 2859: unused values not explicitly dropped by end of block

Meta

rustc --version --verbose:

rustc 1.30.0-nightly (67390c0c3 2018-08-14)
binary: rustc
commit-hash: 67390c0c312ca2d8649ee7aa1e4bfa823f273857
commit-date: 2018-08-14
host: x86_64-unknown-linux-gnu
release: 1.30.0-nightly
LLVM version: 7.0

[jD91mZM2]

Now pushed to stable 1.29. Great.

[Mark-Simulacrum]

Cc @alexcrichton

[alexcrichton]

Ah it looks like this is a symbol conflict error:

rust-lld: error: function signature mismatch: log
>>> defined as (I32, I32, I32) -> void in wasm.wasm.ao2yllok-cgu.2.rcgu.o
>>> defined as (F64) -> F64 in /home/alex/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/wasm32-unknown-unknown/lib/libcompiler_builtins-6955fc9706c7939a.rlib(compiler_builtins-6955fc9706c7939a.compiler_builtins.9y7epby1-cgu.14.rcgu.o)

You'll want to rename your log import as it conflicts with the symbol log in compiler-rt

[jD91mZM2]

Oh, I see, thanks!