elm-solve-deps-wasm
v2.0.0
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A dependency solver for the elm ecosystem
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Dependency solver for Elm, made in WebAssembly
This repo holds a dependency solver for the elm ecosystem compiled to a WebAssembly module. The wasm module is published on npm, so you can easily use it in your JS projects with:
let wasm = require("elm-solve-deps-wasm");
wasm.init();
let use_test = false; // solve for normal dependencies, not test dependencies
let additional_constraints = {}; // no additional package needed
let solution = wasm.solve_deps(
elm_json_config, // the elm.json that we have to solve
use_test,
additional_constraints,
fetchElmJson, // user defined (cf example-offline/dependency-provider-offline.js)
listAvailableVersions // user defined (cf example-offline/dependency-provider-offline.js)
);
Shrinking the .wasm size
Shrinking the generated WebAssembly package to the smallest size possible will benefit everyone using it as a dependency, so here is an attempt at doing it. Most of the info required to shrink the wasm size is available in the rustwasm reference book. Here is a summary of the different techniques we use here.
- Compile with link time optimization (
lto
). In theory, this gives LLVM more opportunities to inline and prune functions. - Use
opt-level = "z"
to optimize for size instead of for speed. - Use the
wee_alloc
allocator which is optimized for size instead of the default allocator, optimized for speed. - Replace panic logic by abort with
panic = "abort"
and withwasm-snip --snip-rust-panicking-code
. - Use
wasm-opt -Oz -o output.wasm input.wasm
on the output of wasm-pack. Remark that it's better to use the latest one from the binaryen project instead of the one shipped with wasm-pack automatically, so we addwasm-opt = false
to wasm-pack config. - Profile the generated wasm with
twiggy
to find optimization opportunities. This requires addingdebug = true
to the release compilation profile, and-g
towasm-opt
.
With the above tricks we start with a .wasm
file weighing 470kb and end with a 251kb file!
Most of it comes from the wasm-opt
tool.
Here is the detail of what each step brings:
- Initial
--release
size: 479kb. - When using
wee_alloc
: 470kb. - When also adding
wasm-opt -Oz
: 366kb. - When also adding
lto = true
andopt-level = "z"
: 276kb. - When also adding
wasm-snip --snip-rust-panicking-code
: 271kb. - When adding
debug = true
and using twiggy, I found out that there was a non-negligeable part of the wasm binary dedicated to formatting f64 numbers. But in fact, this never happens in our use case, so we can snipe it! - When also adding
wasm-snip -p "core::fmt::float::<impl core::fmt::Display for f64>::fmt::.*"
: 251kb.
So in summary, the steps to get the most shrinked wasm module are the following:
wasm-pack build --target nodejs
wasm-snip --snip-rust-panicking-code -p "core::fmt::float::<impl core::fmt::Display for f64>::fmt::.*" -o snipped.wasm pkg/elm_solve_deps_wasm_bg.wasm
wasm-opt -Oz -o output.wasm snipped.wasm
cp output.wasm pkg/elm_solve_deps_wasm_bg.wasm
All that being said, if you don't want to bother installing wasm-snip
and the latest wasm-opt
, you can simply call:
wasm-pack build --profiling --target nodejs
and let the provided wasm-opt do its job, with a generated .wasm
of size 276kb.