Introduce the wasmtime-explorer crate

[fitzgen]

This implements Godbolt Compiler Explorer-like functionality for Wasmtime and Cranelift. Given a Wasm module, it compiles the module to native code and then writes a standalone HTML file that gives a split pane view between the WAT and ASM disassemblies.

THIS IS VERY MUCH AN MVP!!! Tons of stuff we could do with this, very little it actually does so far.

Usage:

$ wasmtime explore test.wasm -o test.explore.html
$ xdg-open test.explore.html

Once visiting the HTML page, you can hover over lines of WAT or asm and the corresponding lines will be highlighted. You can also click to scroll the corresponding line into view.

Here is a little screen recording, although the mouse itself isn't captured so it is a little hard to see what is going on:

Screencast.from.2023-03-09.17-22-06.webm

[fitzgen]

Oh this also depends on publishing a new wasmprinter with the new Printer::offsets_and_lines method.

[jameysharp]

I think it's worth making this not be x86-specific, and of course the wasmprinter changes have to land, but overall this looks entirely reasonable to me. Also, it's super exciting!

[alexcrichton]

Nice! If capstone could compile with wasi-libc then we could also make a web demo out of this :)

[alexcrichton]

All seems reasonable to me! I'm not necessarily reviewing the code too closely but at a high level I like the idea and I like the integration into the wasmtime CLI.

Also FWIW this is sort of a hop-skip-and-a-jump away from getting source code with DWARF debugging information at this point too!

[fitzgen]

Also FWIW this is sort of a hop-skip-and-a-jump away from getting source code with DWARF debugging information at this point too!

Yep, as I said, lots we could do here! Will be nice to just get something landed first tho.