1 files changed, 56 insertions, 0 deletions
diff --git a/thirdparty/preact/config/codemod-strip-tdz.js b/thirdparty/preact/config/codemod-strip-tdz.js
new file mode 100644
index 000000000..a1f07fafe
--- /dev/null
+++ b/thirdparty/preact/config/codemod-strip-tdz.js
@@ -0,0 +1,56 @@
+/* eslint no-console:0 */
+
+
+// parent node types that we don't want to remove pointless initializations from (because it breaks hoisting)
+const BLOCKED = ['ForStatement', 'WhileStatement']; // 'IfStatement', 'SwitchStatement'
+
+/** Removes var initialization to `void 0`, which Babel adds for TDZ strictness. */
+export default (file, api) => {
+	let { jscodeshift } = api,
+		found = 0;
+
+	let code = jscodeshift(file.source)
+		.find(jscodeshift.VariableDeclaration)
+		.forEach(handleDeclaration);
+
+	function handleDeclaration(decl) {
+		let p = decl,
+			remove = true;
+
+		while ((p = p.parentPath)) {
+			if (~BLOCKED.indexOf(p.value.type)) {
+				remove = false;
+				break;
+			}
+		}
+
+		decl.value.declarations.filter(isPointless).forEach( node => {
+			if (remove===false) {
+				console.log(`> Skipping removal of undefined init for "${node.id.name}": within ${p.value.type}`);
+			}
+			else {
+				removeNodeInitialization(node);
+			}
+		});
+	}
+
+	function removeNodeInitialization(node) {
+		node.init = null;
+		found++;
+	}
+
+	function isPointless(node) {
+		let { init } = node;
+		if (init) {
+			if (init.type==='UnaryExpression' && init.operator==='void' && init.argument.value==0) {
+				return true;
+			}
+			if (init.type==='Identifier' && init.name==='undefined') {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	return found ? code.toSource({ quote: 'single' }) : null;
+};