Testing: refactor check-local-changes script

bin/check-local-changes.js

@@ -0,0 +1,55 @@
+/**
+ * External dependencies
+ */
+const SimpleGit = require( 'simple-git' );
+
+SimpleGit()
+	.diff( [ '-U0' ] )
+	.then( ( diff ) => {
+		// npm will introduce changes to a `package-lock.json` file for optional
+		// dependencies varying on environment. If the only changes are the
+		// addition of an "optional" flag in `package-lock.json` file from
+		// `git diff`: we ignore the results.
+		//
+		// See: https://github.com/npm/npm/issues/17722
+
+		// Example input:
+		//
+		// diff --git a/package-lock.json b/package-lock.json
+		// index e8c8a25dc..251af8689 100644
+		// --- a/package-lock.json
+		// +++ b/package-lock.json
+		// @@ -14373 +14373,2 @@
+		// -                       "dev": true
+		// +                       "dev": true,
+		// +                       "optional": true
+		// @@ -14648 +14649,2 @@
+		// -                       "dev": true
+		// +                       "dev": true,
+		// +                       "optional": true
+		const nonOptionalDiff = diff
+			// Strip individual diffs of optional-only.
+			.replace(
+				/@@ .+ @@\n(-.+\n\+.+,\n)?\+.+\"optional\": true,?\n/gm,
+				''
+			)
+			// If no more line diffs remain after above, remove diff heading for file.
+			.replace(
+				/diff --git a\/package-lock.json b\/package-lock.json\nindex \w+..\w+ \d+\n--- a\/package-lock.json\n\+\+\+ b\/package-lock.json\n(?!@@)/,
+				''
+			);
+
+		if ( !! nonOptionalDiff ) {
+			console.error(
+				"There are local uncommitted changes after one or both of 'npm install' or 'npm run docs:build'!\n"
+			);
+			console.log( nonOptionalDiff );
+			process.exitCode = 1;
+		}
+	} )
+	.catch( ( error ) => {
+		console.error(
+			'Checking local changes failed!\n\n' + error.toString() + '\n'
+		);
+		process.exitCode = 1;
+	} );

package.json

@@ -248,7 +248,7 @@
 		"changelog": "node ./bin/plugin/cli.js changelog",
 		"check-licenses": "concurrently \"wp-scripts check-licenses --prod --gpl2 --ignore=@react-native-community/cli,@react-native-community/cli-platform-ios\" \"wp-scripts check-licenses --dev\"",
 		"precheck-local-changes": "npm run docs:build",
-		"check-local-changes": "( git diff -U0 | xargs -0 node bin/process-git-diff ) || ( echo \"There are local uncommitted changes after one or both of 'npm install' or 'npm run docs:build'!\" && git diff --exit-code && exit 1 );",
+		"check-local-changes": "node ./bin/check-local-changes.js",
 		"dev": "npm run build:packages && concurrently \"wp-scripts start\" \"npm run dev:packages\"",
 		"dev:packages": "concurrently \"node ./bin/packages/watch.js\" \"tsc --build --watch\"",
 		"distclean": "rimraf node_modules packages/*/node_modules",