use command-exists instead of manually checking if cmd is avalible

this commit replaces old code that was designed to determine if things like rustup or wasm-gc were installed
the new implementation uses the npm package command-exists, which gives us better async, errs, etc

Author: thomashorrobin

packages/react-scripts/package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-scripts-rust",
-  "version": "2.0.15",
+  "version": "2.0.16",
   "description": "Configuration and scripts for using Rust with Create React App",
   "repository": "thomashorrobin/create-react-app-rust",
   "license": "MIT",
@@ -32,6 +32,7 @@
     "bfj": "6.1.1",
     "case-sensitive-paths-webpack-plugin": "2.1.2",
     "chalk": "2.4.1",
+    "command-exists": "^1.2.8",
     "css-loader": "1.0.0",
     "dotenv": "6.0.0",
     "dotenv-expand": "4.2.0",

packages/react-scripts/scripts/utils/rustUtils.js

@@ -1,5 +1,6 @@
 const execSync = require('child_process').execSync;
 const chalk = require('chalk');
+const commandExistsSync = require('command-exists').sync;
 
 module.exports = {
   build: () => {
@@ -13,19 +14,14 @@ module.exports = {
       console.log(chalk.bold.red('error compiling rust'));
     }
   },
-  isRustInstalled: () => {
-    try {
-      execSync('rustup show');
-      return true;
-    } catch (error) {
-      return false;
-    }
-  },
+  isRustInstalled: () => commandExistsSync('rustup'),
   installRustWebAssemblyTools: () => {
-    try {
-      execSync('cargo install wasm-gc', { stdio: 'inherit' });
-    } catch {
-      console.log(`${chalk.bold.red('error installing wasm-gc')} please install manually ${chalk.red('cargo install wasm-gc')}')`);
+    if (!commandExistsSync('wasm-gc')) {
+      try {
+        execSync('cargo install wasm-gc', { stdio: 'inherit' });
+      } catch {
+        console.log(`${chalk.bold.red('error installing wasm-gc')} please install manually ${chalk.red('cargo install wasm-gc')}')`);
+      }
     }
     execSync(
       'rustup target add wasm32-unknown-unknown --toolchain nightly',