Generating correct assignments for live bindings updated with UpdateExpressions (#7489)

Fixes #7488

packages/babel-helper-simple-access/src/index.js

@@ -29,8 +29,9 @@ const simpleAssignmentVisitor = {
         (path.parentPath.isExpressionStatement() && !path.isCompletionRecord())
       ) {
         // ++i => (i += 1);
+        const operator = path.node.operator == "++" ? "+=" : "-=";
         path.replaceWith(
-          t.assignmentExpression("+=", arg.node, t.numericLiteral(1)),
+          t.assignmentExpression(operator, arg.node, t.numericLiteral(1)),
         );
       } else {
         const varName = path.scope.generateDeclaredUidIdentifier("old").name;

packages/babel-plugin-transform-modules-commonjs/test/fixtures/update-expression/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["external-helpers", ["transform-modules-commonjs"]]
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/update-expression/suffix/negative/input.js

@@ -0,0 +1,7 @@
+export let diffLevel = 0;
+
+export function diff() {
+  if (!--diffLevel) {
+    console.log("hey");
+  }
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/update-expression/suffix/negative/output.js

@@ -0,0 +1,15 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true,
+});
+exports.diff = diff;
+exports.diffLevel = void 0;
+let diffLevel = 0;
+exports.diffLevel = diffLevel;
+
+function diff() {
+  if (!(exports.diffLevel = diffLevel = diffLevel - 1)) {
+    console.log("hey");
+  }
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/update-expression/suffix/positive/input.js

@@ -0,0 +1,7 @@
+export let diffLevel = 0;
+
+export function diff() {
+  if (!++diffLevel) {
+    console.log("hey");
+  }
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/update-expression/suffix/positive/output.js

@@ -0,0 +1,15 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true,
+});
+exports.diff = diff;
+exports.diffLevel = void 0;
+let diffLevel = 0;
+exports.diffLevel = diffLevel;
+
+function diff() {
+  if (!(exports.diffLevel = diffLevel = diffLevel + 1)) {
+    console.log("hey");
+  }
+}