Implement the module linking proposal in Wasmtime

[alexcrichton]

I plan to use this as a tracking issue for the module linking proposal in Wasmtime. I'll be updating this description over time as I find time and as work is done:

• Implement in wasm-tools (validation, text, binary, etc) Initial implementation of module linking wasm-tools#26, wasmpaser: Validate nested modules wasm-tools#30, Disallow module linking sections by default wasm-tools#38, Rewrite wasmparser's module parser and validator wasm-tools#40, ...
• Update wasmparser used by Wasmtime to understand module linking Validate modules while translating #2059
• Initial groundwork for compiling many modules at once Start compiling module-linking modules  #2093
• Implement the alias section Implement the module linking alias section  #2451
• Implement the instance section Instantiate nested modules for module linking #2447
• Implement module export/import Implement imported/exported modules/instances #2461
• Implement instance export/import Implement imported/exported modules/instances #2461
• Ensure the Rust API exposes module linking well
• Implement module linking in the C API Update the C API with module linking support #2472
• Implement module linking for one of wasmtime-{go,dotnet,py} Add support for the module linking proposal wasmtime-py#47, Implement module linking proposal wasmtime-go#46
• Implement fuzzing for module linking

Implementation Notes

Some miscenalleous notes on the implementation and how this is being implemented:

• Per-module data structures are intended to continue to be per-module, only wasmtime::Module will internally have a list of modules to select from.
• Aliases are expected to be implemented under the hood as imports.
  • It's expected that instantiation will pass in a Resolver for the actual imports, as well as the "surrounding environment" which is probably "the list of all other modules that came from the original wasm file".
  • JIT code will call an aliased function from an imported instance as if it were an imported function. (similar for tables/globals/etc)

Open questions:

• What should wasm2obj do for multi-module wasm files?
• What should the runtime representation in wasmtime-jit be for imported instances and imported modules?

[tschneidereit]

Update wasmparser used by Wasmtime to understand module linking

It seems like this is done?

[alexcrichton]

Indeed!