Support for Wasm?

[mfreeborn]

I'd really like to be able to run my Web Assembly tests and get coverage reports for them.

First issue, can I specify a custom binary to run e.g. instead of cargo test, my test command is wasm-pack test --node.

Second issue, I get a compile error when trying to build on wasm32-unknown-unknown:

$ cargo llvm-cov --target wasm32-unknown-unknown
info: when --target option is used, coverage for proc-macro and build script will not be displayed because cargo does not pass RUSTFLAGS to them
   Compiling cfg-if v1.0.0
   Compiling scoped-tls v1.0.0
   Compiling ag-grid-derive v0.1.0
error[E0463]: can't find crate for `profiler_builtins`
  |
  = note: the compiler may have been built without the profiler runtime

For more information about this error, try `rustc --explain E0463`.
error: could not compile `cfg-if` due to previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `scoped-tls` due to previous error

Is the above possible?

[taiki-e]

As for the second issue, it is the same issue as https://github.com/rust-lang/rust/issues/81684.

One or both of the following may work:

• support minicov (but, I guess we can already handle minicov by just passing some flags as rustflags)
• use wasi with own toolchain built with profiler = true and this patch (once this PR is merged, building own toolchain may no longer be necessary)

---

As for the first issue, I think we can add a subcommand as we did for nextest. something like: cargo llvm-cov wasm-pack test --node.

That said, the second issue needs to be resolved first.

[njelich]

@taiki-e Hey, can we do anything to help develop this feature? The PR mentioned above in Rust repos was closed, and a lot has changed in the past year.

[taiki-e]

I don't think the situation has changed much on this issue. Someone will need to either contribute to rustc to improve the situation (e.g., by taking over a PR that closed as inactive) or investigate (and document) how to make cargo-llvm-cov work with a profiler-builtins alternative.

[fzyzcjy]

Hi, is there any updates? Thanks! (I guess no...? :/ )

[njelich]

Actually. Here is a spicy boy I made.

https://github.com/hknio/wasmcov

It doesn't use cargo-llvm-cov, but uses the llvm-cov package directly.

[aDogCalledSpot]

With https://github.com/rustwasm/wasm-bindgen/pull/3782, I think we can follow up here.

We could do something like cargo llvm-cov --wasm-bindgen test to generate the profraw with wasm-pack and then process it.

An annoying thing is that we have to use --emit=llvm-ir because llvm-cov can't get the debug info from the .wasm (despite the info being in there). So we would have to run clang target/wasm32-unknown-unknown/debug/deps/{file_name}.ll -Wno-override-module -c -o {file_name}.o and then search for this .o as the binary for the reporting.

I would really love this. It would mean you can merge normal tests with wasm_bindgen_tests easily.