WASM: shipping the runtime module

[pkel]

Compiled-to-wasm contracts depend on a runtime.wasm module for execution. This module is implemented in another language (currently AssemblyScript, see /runtimes/assemblyscript). The module has to be shipped as part of the qcert opam package.

Currently, we use a dune to

1. build runtime.wasm in the runtime tree
2. copy runtime.wasm to the compiler tree
3. translate the binary file to a OCaml hex-encoded string in wasm_runtime.ml
4. (after compilation) read the binary wasm module from Wasm_runtime.runtime_wasm OCaml module

The rules looks like this

(rule
  (target runtime.wasm)
  (deps ../runtimes/assemblyscript/assembly/index.ts)
  (mode (promote (into wasm)))
  (action
    (progn
      (system "cd ../../../runtimes/assemblyscript && npm run asbuild:untouched")
      (with-stdout-to runtime.wasm
        (system "cat ../../../runtimes/assemblyscript/build/untouched.wasm"))
    )
  )
)

(rule
  (target wasm_runtime.ml)
  (deps runtime.wasm)
  (action
    (with-stdout-to wasm_runtime.ml
      (progn (echo "let runtime_wasm = \"")
             (run ../tools/binary_to_string.exe runtime.wasm)
             (echo "\"\n")
      )
    )
  )
)

Practical, but not particularly nice.

Dune (recently?!) added support for shipping additional files and locate/load them at runtime. It's marked experimental in the dune documentation. As soon as there is a stable API, we might consider replacing the above mechanism with the new.

[pkel]

The first rule navigates the file system with relative paths. This does not work if qcert is symlink into another project.

Additionally, the use of npm breaks opam build.

Idea: move the two rules into the assemblyscript dir, create the ml file there, add dune file and create library. Dune will figure out the locations for us

[jeromesimeon]

For reference, error when doing opam install .

### output ###
# Use Stdlib instead.
# [...]
# If you need to stay compatible with OCaml < 4.07, you can use the 
# stdlib-shims library: https://github.com/ocaml/stdlib-shims
File "compiler/dune", line 34, characters 0-253:
# 34 | (rule
# 35 |   (target wasm_runtime.ml)
# 36 |   (deps runtime.wasm)
# ....43 |     )
# 44 |   )
# 45 | )
# Error: No rule found for compiler/runtime.wasm

[pkel]

Progress in 48bfd7f.