Do not unpack array patterns that update a referenced binding

packages/babel-plugin-transform-destructuring/src/index.js

@@ -44,13 +44,23 @@ export default declare((api, options) => {
     return false;
   }
 
-  const arrayUnpackVisitor = {
-    ReferencedIdentifier(path, state) {
-      if (state.bindings[path.node.name]) {
-        state.deopt = true;
-        path.stop();
-      }
-    },
+  const STOP_TRAVERSAL = {};
+
+  // NOTE: This visitor is meant to be used via t.traverse
+  const arrayUnpackVisitor = (node, ancestors, state) => {
+    if (!ancestors.length) {
+      // Top-level node: this is the array literal.
+      return;
+    }
+
+    if (
+      t.isIdentifier(node) &&
+      t.isReferenced(node, ancestors[ancestors.length - 1]) &&
+      state.bindings[node.name]
+    ) {
+      state.deopt = true;
+      throw STOP_TRAVERSAL;
+    }
   };
 
   class DestructuringTransformer {
@@ -282,7 +292,13 @@ export default declare((api, options) => {
       // deopt on reference to left side identifiers
       const bindings = t.getBindingIdentifiers(pattern);
       const state = { deopt: false, bindings };
-      this.scope.traverse(arr, arrayUnpackVisitor, state);
+
+      try {
+        t.traverse(arr, arrayUnpackVisitor, state);
+      } catch (e) {
+        if (e !== STOP_TRAVERSAL) throw e;
+      }
+
       return !state.deopt;
     }
 

packages/babel-plugin-transform-destructuring/test/fixtures/regression/8528/input.js

@@ -0,0 +1,4 @@
+function isBetween(x, a, b) {
+  if (a > b) [a, b] = [b, a];
+  return x > a && x < b;
+}

packages/babel-plugin-transform-destructuring/test/fixtures/regression/8528/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-destructuring"]
+}

packages/babel-plugin-transform-destructuring/test/fixtures/regression/8528/output.js

@@ -0,0 +1,9 @@
+function isBetween(x, a, b) {
+  if (a > b) {
+    var _ref = [b, a];
+    a = _ref[0];
+    b = _ref[1];
+  }
+
+  return x > a && x < b;
+}