From f1515265a29704dbecc183efb7ed9dcd3057fa41 Mon Sep 17 00:00:00 2001
From: Christopher Serr <christopher.serr@gmail.com>
Date: Tue, 8 Nov 2022 01:18:32 +0100
Subject: [PATCH] Build Rust's `std` with immediate abort (#746)

We generally want the wasm file to be as compact as possible. However
because there's so many paths in Rust code that could panic, but don't
ever in practice as they are meant to signal bugs, the wasm file has to
keep around all those panic paths, and even worse, all the code for
formatting the panic messages for all those different types that could
be involved in a panic. This bloats the binary a lot. There's a nightly
feature to build the standard library as part of your compilation and
with that you can pass various features to the standard library, just
like with any other crate. And one of those features is to remove all
the formatting machinery from the panics and just immediately abort,
resulting in smaller binaries. On top of that by building the standard
library ourselves we also get to build it with all our target features,
meaning that its code will make use of all the additional WebAssembly
instructions that have been added since the MVP. So this essentially is
a big win. However this forces us to use the nightly compiler, but it
usually is actually quite stable. We won't be using any nightly features
of the language itself and only optionally use the compiler in our CI,
so the stable compiler continues to work just fine for local
development.
---
 .github/workflows/ci.yml | 5 ++++-
 buildCore.js             | 9 +++++++--
 package.json             | 1 +
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c258999..94318c4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,6 +45,9 @@ jobs:
 
     - name: Install Rust
       uses: hecrj/setup-rust-action@v1
+      with:
+        rust-version: nightly
+        components: rust-src
 
     - name: Install target
       run: rustup target add wasm32-unknown-unknown
@@ -75,7 +78,7 @@ jobs:
     - name: Build Core
       run: |
         set -e
-        npm run build:core:production
+        npm run build:core:deploy
 
     - name: Set up tslint matcher
       run: echo "::add-matcher::.github/workflows/tslint.json"
diff --git a/buildCore.js b/buildCore.js
index 7d583fd..35ffebd 100644
--- a/buildCore.js
+++ b/buildCore.js
@@ -2,14 +2,19 @@ import { execSync } from "child_process";
 import fs from "fs";
 
 let buildFlags = "";
+let toolchain = "";
 let targetFolder = "debug";
 if (process.argv.some((v) => v === "--production")) {
     buildFlags = "--release";
     targetFolder = "release";
 }
+if (process.argv.some((v) => v === "--nightly")) {
+    toolchain = "+nightly";
+    buildFlags += " -Z build-std=std,panic_abort -Z build-std-features=panic_immediate_abort";
+}
 
 execSync(
-    "cargo run",
+    `cargo ${toolchain} run`,
     {
         cwd: "livesplit-core/capi/bind_gen",
         stdio: "inherit",
@@ -17,7 +22,7 @@ execSync(
 );
 
 execSync(
-    `cargo rustc -p livesplit-core-capi --crate-type cdylib --features wasm-web --target wasm32-unknown-unknown ${buildFlags}`,
+    `cargo ${toolchain} rustc -p livesplit-core-capi --crate-type cdylib --features wasm-web --target wasm32-unknown-unknown ${buildFlags}`,
     {
         cwd: "livesplit-core",
         stdio: "inherit",
diff --git a/package.json b/package.json
index dc37777..08335e5 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "build": "webpack",
     "build:core": "node buildCore.js",
     "build:core:production": "node buildCore.js --production",
+    "build:core:deploy": "node buildCore.js --production --nightly",
     "lint": "tslint --project tsconfig.json",
     "publish": "webpack --mode production",
     "serve": "webpack serve",