Tooling: Ignore optional changes to lockfile

bin/process-git-diff.js

@@ -0,0 +1,33 @@
+// npm will introduce changes to a `package-lock.json` file for optional
+// dependencies varying on environment. Disregard from a git diff result when
+// only changes are addition of "optional" flag in `package-lock.json` file.
+//
+// See: https://github.com/npm/npm/issues/17722
+
+// Example usage:
+//
+// git diff -U0 | xargs -0 node bin/process-git-diff
+
+// 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 hasNonOptionalDiff = !! ( process.argv[ 2 ] || '' )
+	// 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(?!@@)/, '' );
+
+// Exit with error code if, after replace, changes still exist.
+process.exit( hasNonOptionalDiff ? 1 : 0 );

package.json

@@ -152,7 +152,7 @@
 		"check-engines": "check-node-version --package",
 		"check-licenses": "concurrently \"wp-scripts check-licenses --prod --gpl2\" \"wp-scripts check-licenses --dev\"",
 		"precheck-local-changes": "npm run docs:build",
-		"check-local-changes": "git diff --exit-code > /dev/null || ( echo \"There are local uncommitted changes after one or both of 'npm install' or 'npm run docs:build'!\" && exit 1 );",
+		"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'!\" && exit 1 );",
 		"ci": "concurrently \"npm run lint\" \"npm run test-unit:coverage-ci\" \"npm run check-local-changes\"",
 		"predev": "npm run check-engines",
 		"dev": "npm run build:packages && concurrently \"cross-env webpack --watch\" \"npm run dev:packages\"",