Project builds in debug mode, fails with --release

[ndarilek]

I'm hacking on this code. If I run:

cargo web build --target-webasm-emscripten

The project builds fine. If I run:

cargo web build --target-webasm-emscripten --release

the build fails with screens of errors, at the top of which is:

  = note: WARNING:root:emcc: cannot find library "SDL2"

The errors look like so:

          WARNING:root:object /tmp/emscripten_temp_3wyyWe_archive_contents/ncollide-cfdd2aa6ffc25dc6.ncollide0.rust-cgu.bytecode.encoded is not valid, cannot link

This is with a stock Emscripten environment under Linux (I.e. the prebuilt 1.37.27 binaries.) No other change is made in the environment beyond adding --release to the build command, and I'm using latest Rust stable.

[koute]

Does it work with another copy of Emscripten (e.g. from your distro's repos?)

If you build it in debug mode does it also run properly?

Does it also fail to build when compiling to asmjs?

[ndarilek]

Does `cargo web start ...`? run a debug build? If so, then yes, it does build and run correctly in debug mode. I see the same behavior with `cargo web build` and `cargo web build --release`, so I assume asmjs has the same issue. Crap, sorry, I removed my emsdk build when the pre-built 1.37.27 was released. Running low on HD space, and your builds are much more compact than the 20+GB from-source builds. But I'm pretty sure this failed with those, though, as I've been using emsdk until .27. If knowing this would help, I can rebuild emsdk and try again.

[ndarilek]

Just restored emsdk from my January 1st backup Same exact behavior. Seems to not find SDL2 when built in the release configuration. Not sure if the object generation errors are due to the compiler or an artifact of other missing libs, but they're present in every Emscripten I've tried.

[koute]

Hmmm... can you try to add a [profile.release] section to your Cargo.toml and try setting codegen-units = 1, and if that doesn't work then lto = true too?

[ndarilek]

With: ``` [profile.release] codegen-units = 1 lto = true ``` the error count is vastly reduced: ```   = note: WARNING:root:emcc: cannot find library "SDL2"           WARNING:root:object /tmp/emscripten_temp_DpyisF_archive_contents/compiler_builtins-bd7cc5ada1e908e0.compiler_builtins0.rust-cgu.bytecode.encoded is not valid, cannot link ``` Without that section, I have pages of warnings like those on the last line. As per your earlier suggestion, I have: ``` link-args = ["-s", "USE_SDL=2"] ``` in my Web.toml. Given that SDL2 isn't found, is it possible this file is only evaluated in debug mode, or that I have to specifically add a release profile?

[koute]

Hmm... it should work in both debug and release modes, unless we have a bug.

You can temporairly get rid of Web.toml and try specifying it manually:

export RUSTFLAGS="-C link-arg=-s -C link-arg=USE_SDL=2"

Then compile in debug mode to verify that it does indeed work, and then you can try to compile in release mode again. You can also try to do cargo build --release --target="wasm32-unknown-emscripten" while having those RUSTFLAGS exported.

[koute]

@ndarilek Since I've finished what I was doing I took a look at your repository and found the reason for your issue.

The SDL2 error is a red herring. Emscripten runs uglify when building in release mode which rejects ES6+ syntax.

In your tts.rs you need to change this line:

let u = new SpeechSynthesisUtterance();

into this:

var u = new SpeechSynthesisUtterance();

(Also add a ; at the end of the speechSynthesis.speak(u) line.)

Then your code will compile in release mode.

[ndarilek]

Perfect, thanks! Just filed a Rust compiler issue this morning. I'll post this update there--would be helpful if we got a better error message.

[koute]

I have on my TODO list syntax checking for the JS snippets before handing it off to Emscripten so that we can avoid situations like this, but yeah, unfortunately that's mostly an Emscripten issue.

[koute]

So since your problem is resolved I'll close this issue; if you have any further problems feel free to create a new one.