Use the newly fixed debugging information

[daxpedda]

Just dropping some random thoughts before I forget them.

• Using it in wasm-bindgen-test instead of console_error_panic_hook (don't replace it entirely because we still need the panic message).
• Add a new documentation page noting how to actually deploy it.
  • Generate sourcemaps, e.g. using wasm2map.
  • Strip DWARF in case of sourcemaps.
  • Notes on browser support and how to serve source files if not bundled.
• Maybe think about adding an option to generate source maps or split debug info directly in wasm-bindgen, but I would argue this would be more the domain of wasm-pack and co.

[ranile]

A page in the documentation about this information would be very helpful

[xxshady]

for some reason wasm2map generates empty sourcemap file when i call it on .wasm generated by wasm-pack
{"version":3,"names":[],"sources":[""],"sourcesContent":[],"mappings":""}

commands i use:
wasm-pack build --dev --target no-modules
cargo wasm2map --bundle-sources -p <generated .wasm> -b http://127.0.0.1:8080

it generates correct sourcemap for .wasm from target/wasm32-unknown-unknown/debug though (but its not usable with wasm-pack's .wasm)

[daxpedda]

You have to use the --keep-debug CLI option to not discard the DWARF information when post-processing with wasm-bindgen.

How to do that with wasm-pack is something you might want to ask there.

[xxshady]

yeah, thank you, with --keep-debug wasm2map generates correct sourcemap, i did not found how to enable it in wasm-pack, but using wasm-bindgen CLI directly it worked:

1. cargo build --target wasm32-unknown-unknown
2. wasm-bindgen --target <your target> --out-dir pkg --keep-debug target/wasm32-unknown-unknown/debug/<crate name>.wasm
   (if you don't have wasm-bindgen CLI installed: cargo install wasm-bindgen-cli)
3. cargo wasm2map pkg/<crate name>_bg.wasm
   (you probably also need to provide other flags if your target is browser or nodejs, see wasm2map example)
4. sourcemap should be available in pkg/<crate name>_bg.wasm.map

note: i only tested it with wasm-bindgen --target no-modules, not sure if others will work the same

also, if you are building something outside of browser or nodejs (like me) where sourcemaps are not supported out of the box, here is how you can use sourcemap manually to get original source code line and column:

1. cargo wasm2map pkg/<crate name>.wasm --bundle-sources --patch --base-url blabla
   (--base-url blabla because it doesnt matter anyway, but required by --bundle-sources)

2. for example we have this frame:
   at rust_wasm.wasm.rust_wasm::script_events::test_script_events::____test_panic4____::he9b091250693a65d (wasm://wasm/rust_wasm.wasm-01976b8a:wasm-function[2428]:0xbf5ed)
0xbf5ed is the column, the line is always 1 (because .wasm is binary as i understand)

3. now you can pass line and colum your sourcemap resolver (anything that can resolve sourcemaps v3)

4. i'm gonna use source-map-cli for it

5. source-map-cli doesn't support hex numbers, so converting column to decimal first: 783853

6. npx source-map-cli resolve pkg/rust_wasm_bg.wasm.map 1 783853

Maps to .../src/script_events.rs:300:4 

    panic!("test panic");
    ^

note: cargo wasm2map pkg/<crate name>_bg.wasm is already enough to get sourcemap but source-map-cli requires bundled source code

[andrewbaxter]

I didn't quite get this working. IIUC the current required steps are:

1. Build with debug info (debug mode, or debug=true in profile.release)
2. Run wasm-bindgen with --keep-debug
3. Do wasm2map. I did it via the rust library, and for x.wasm wrote to x.wasm.map and patched with url "x.wasm.map" (no absolute url).

I got the same wasm bytecode backtrace, no rust line numbers.

Clicking on the lines did attempt to pull up the source map, but the change to wasm2map to include the source files hasn't been released yet so the individual files were missing (as expected).

I did 1-3 above plus console-error-panic-hook and no improvement.