web: Use RUSTC_BOOTSTRAP for MVP vanilla WASM module instead of nightly

Author: danielhjacobs

web/README.md

@@ -45,6 +45,7 @@ to update to the latest stable version of rust. You may run `rustup update` to d
 rust using the above instructions).
 
 For the compiler to be able to output WebAssembly, an additional target has to be added to it: `rustup target add wasm32-unknown-unknown`
+Because we use `RUSTC_BOOTSTRAP` in order to use certain Nightly flags with stable Rust you will also need to run `rustup component add rust-src`.
 
 #### Java
 
@@ -106,7 +107,6 @@ In this project, you may run the following commands to build all packages:
     -   There is `npm run build:dual-wasm` as well, to build a second WebAssembly module that makes use of some WebAssembly extensions,
         potentially resulting in better performance in browsers that support them, at the expense of longer build time.
     -   `npm run build:repro` enables reproducible builds. Note that this also requires a `version_seal.json`, which is not provided in the normal Git repository - only specially-marked reproducible source archives. Running this without a version seal will generate one based on the current state of your environment.
-    -   With either of the prior two commands, you can set the environment variable `BUILD_WASM_MVP=1`. This will build the vanilla WASM module using nightly Rust and disable all WebAssembly features that Rust enables by default. You will first need to run the command `rustup target add wasm32-unknown-unknown --toolchain nightly` so nightly Rust can also output WebAssembly.
 
 From here, you may follow the instructions to [use Ruffle on your website](packages/selfhosted/README.md),
 run a demo locally with `npm run demo`, or [install the extension in your browser](https://github.com/ruffle-rs/ruffle/wiki/Using-Ruffle#browser-extension).

web/packages/core/tools/build_wasm.ts

@@ -49,20 +49,12 @@ function cargoBuild({
     rustFlags?: string[];
     extensions?: boolean;
 }) {
-    let args =
-        !extensions && process.env["BUILD_WASM_MVP"]
-            ? [
-                  process.env["NIGHTLY_VERSION"]
-                      ? `+nightly-${process.env["NIGHTLY_VERSION"]}`
-                      : "+nightly",
-                  "build",
-                  "--locked",
-                  "-Z",
-                  "build-std=std,panic_abort",
-                  "--target",
-                  "wasm32-unknown-unknown",
-              ]
-            : ["build", "--locked", "--target", "wasm32-unknown-unknown"];
+    let args = ["build", "--locked", "--target", "wasm32-unknown-unknown"];
+    if (!extensions) {
+        args.push("-Z");
+        args.push("build-std=std,panic_abort");
+    }
+
     if (profile) {
         args.push("--profile", profile);
     }
@@ -88,6 +80,7 @@ function cargoBuild({
     execFileSync("cargo", args, {
         env: Object.assign(Object.assign({}, process.env), {
             RUSTFLAGS: totalRustFlags,
+            RUSTC_BOOTSTRAP: extensions ? '0' : '1',
         }),
         stdio: "inherit",
     });
@@ -110,13 +103,12 @@ function buildWasm(
         );
         wasmBindgenFlags.push("--reference-types");
         wasmOptFlags.push("--enable-reference-types");
+    } else {
+        rustFlags.push("-C", "target-cpu=mvp");
     }
     let originalWasmPath;
     if (wasmSource === "cargo" || wasmSource === "cargo_and_store") {
         console.log(`Building ${flavor} with cargo...`);
-        if (process.env["BUILD_WASM_MVP"]) {
-            rustFlags.push("-C", "target-cpu=mvp");
-        }
         cargoBuild({
             profile,
             rustFlags,