Map error locations to original location via source map

[nomeata]

Thanks to @FloorLamp we now have source maps, and we can use this to post-process the trap messages by wasm to make them both more useful, and more stable as the compiler output changes, by mapping them to the original location in the actorscript file.

This needs a bit more cleanup, in particular about the plumbing where to find this script.

I am tempted to redo the whole test suite in bash or something.

[nomeata]

Ok, this is good to go, but I fear that it will interfere with @rossberg and @crusso’s current development environment, so I’d like to get a review here.

Basically there is a small useful script (happens to be written in JS) that I would like to use in the test suite, called source-map-pp. These are the ways you can use this now:

• Use nix-shell -A native to enter an environment with all used tools (including dsh, wasm etc.) available. Does not interfere with your usual environment.
• Use nix-env -i -f test/source-map-pp -A package once to add souce-map-pp to your PATH, and then continue to use make as before.
• Avoid nix, and use npm install in test/source-map-pp, and continue to use make as before.

So basically either deal with npm or nix…

The stability of the trap locations in the testsuite is only a minor thing (and I can still use source-map-pp to debug my code gen manually). OTOH, if you have to deal with nix anyways eventually, then this would be nice to have…

[nomeata]

I guess now that everyone is using nix, this little feature would be possible. Although it is only half as useful as long as v8 does not report the position of an Unreachable … I think I will close this for now, and maybe come back to it if the itch it scratches gets stronger.

[rossberg]

V8 can actually report it, but the C API currently doesn't propagate that information. I just opened WebAssembly/wasm-c-api#54 for this.