tests fail if start attribute is present

[Urhengulas]

Describe the Bug

Testing of wasm-bindgen lib fails if #[wasm_bindgen(start)] is present (for both browser and node).

Error Message

$ wasm-pack test
[INFO]: Checking for the Wasm target...
   Compiling rav1e_js v0.1.0 (/home/urhengulas/Documents/github.com/xiph/rav1e/rav1e_js)
error: linking with `rust-lld` failed: exit code: 1

### ----- stripped ----- ###

  = note: rust-lld: error: function signature mismatch: main
          >>> defined as () -> void in /path/to/rav1e/target/wasm32-unknown-unknown/debug/deps/librav1e_js.rlib(rav1e_js.e16cnisiuzwaayg.rcgu.o)
          >>> defined as (i32, i32) -> i32 in /path/to//rav1e/target/wasm32-unknown-unknown/debug/deps/web-17ed0dcdfd20c376.2kwhsv3emygdoj04.rcgu.o

### ----- stripped ---- ###

error: entry symbol `main` declared multiple times
  |
  = help: did you use `#[no_mangle]` on `fn main`? Use `#[start]` instead

error: aborting due to previous error

error: could not compile `rav1e_js`.

### ----- stripped ----- ###

Caused by: failed to execute `cargo build`: exited with exit code: 101
  full command: "cargo" "build" "--tests" "--target" "wasm32-unknown-unknown"

Steps to Reproduce

# 1. clone repo
git clone https://github.com/Urhengulas/rav1e.git
# 2. checkout commit
git checkout 46283554cfc093fb6721557068b3242794544226
# 3. go into subfolder
cd rav1e_js/
# 4. run tests
wasm-pack test --node

Expected Behavior

I expect wasm-pack test --node to run all wasm-bindgen tests for node.

And since the wasm-bindgen books says here:

The start function will not be executed when testing.

I also expect it to not be executed. (Maybe not even part of the build).

Actual Behavior

The command fails and doesn't run any tests.

Additional Context

wasm-pack build runs without any problems and also the pkg/ works.

[alexcrichton]

This says that main is defined multiple times in two crates, which I think is unrelated to #[wasm_bindgen(start)]? Can you see why the main symbol is defined twice?

[Urhengulas]

Thanks for the fast answer @alexcrichton.

No, I didn't define the #[wasm_bindgen(start)] twice.
I now solved the issue by renaming the function I annotated with the attribute from main to main_js.

I got the hint from rust-gamedev/wg#51:

wasm-bindgen doesn't currently support main - you have to use the wasm_bindgen(start) attribute on a public function instead, and that function can't be main

I couldn't find a reason why this solves the problem, but it does.

I will send a PR changing this in the example in the rust-bindgen book.

[alexcrichton]

Ok thanks for the follow-up! It sounds like this isn't a bug in wasm-bindgen so I'm going to close this.

[nstoddard]

I just encountered this issue, and the workaround of renaming main to main_js fails for me with the error <path to output file>.wasm: Syntax error: end of file unexpected. Everything works fine when building normally; the issue only occurs with cargo test.

Is there another workaround? Does anyone know if this is a bug in rustc, cargo, or wasm-bindgen?