Fix plugin-transform-block-scoping const violations (#13248)

* Fix plugin-transform-block-scoping const violations

Fixes #13245

* Replace `a++` with `+a` where const violation

* Remove assignment where const violation

* Remove assignment for `&&=`, `||=`, `??=` where const violation

* Shorten test

packages/babel-plugin-transform-block-scoping/src/index.js

@@ -433,17 +433,49 @@ class BlockScoping {
         ]);
 
         if (violation.isAssignmentExpression()) {
-          violation
+          const { operator } = violation.node;
-            .get("right")
+          if (operator === "=") {
-            .replaceWith(
+            violation.replaceWith(
-              t.sequenceExpression([throwNode, violation.get("right").node]),
+              t.sequenceExpression([violation.get("right").node, throwNode]),
             );
+          } else if (["&&=", "||=", "??="].includes(operator)) {
+            violation.replaceWith(
+              t.logicalExpression(
+                operator.slice(0, -1),
+                violation.get("left").node,
+                t.sequenceExpression([violation.get("right").node, throwNode]),
+              ),
+            );
+          } else {
+            violation.replaceWith(
+              t.sequenceExpression([
+                t.binaryExpression(
+                  operator.slice(0, -1),
+                  violation.get("left").node,
+                  violation.get("right").node,
+                ),
+                throwNode,
+              ]),
+            );
+          }
         } else if (violation.isUpdateExpression()) {
           violation.replaceWith(
-            t.sequenceExpression([throwNode, violation.node]),
+            t.sequenceExpression([
+              t.unaryExpression("+", violation.get("argument").node),
+              throwNode,
+            ]),
           );
         } else if (violation.isForXStatement()) {
           violation.ensureBlock();
+          violation
+            .get("left")
+            .replaceWith(
+              t.variableDeclaration("var", [
+                t.variableDeclarator(
+                  violation.scope.generateUidIdentifier(name),
+                ),
+              ]),
+            );
           violation.node.body.body.unshift(t.expressionStatement(throwNode));
         }
       }

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/assignment-expression/exec.js

@@ -0,0 +1,62 @@
+const state1 = {};
+expect(function() {
+  const a = 3;
+  let b = 1;
+  state1.getA = () => a;
+  state1.getB = () => b;
+
+  a += b++;
+}).toThrow('"a" is read-only');
+expect(state1.getA()).toBe(3); // Assignment did not succeed
+expect(state1.getB()).toBe(2); // `b++` was evaluated before error thrown
+
+const state2 = {};
+expect(function() {
+  const a = {
+    valueOf() {
+      state2.valueOfIsCalled = true;
+    }
+  };
+  state2.a = a;
+  state2.getA = () => a;
+  state2.getB = () => b;
+
+  let b = 1;
+  a += b++;
+}).toThrow('"a" is read-only');
+expect(state2.getA()).toBe(state2.a); // Assignment did not succeed
+expect(state2.getB()).toBe(2); // `b++` was evaluated before error thrown
+expect(state2.valueOfIsCalled).toBe(true); // `a` was read before error thrown
+
+const state3 = {};
+expect(function() {
+  const a = 32;
+  let b = 1;
+  state3.getA = () => a;
+  state3.getB = () => b;
+
+  a >>>= ++b;
+}).toThrow('"a" is read-only');
+expect(state3.getA()).toBe(32); // Assignment did not succeed
+expect(state3.getB()).toBe(2); // `++b` was evaluated before error thrown
+
+const state4 = {};
+expect(function() {
+  const a = 1;
+  let b = 1;
+  state4.getA = () => a;
+  state4.getB = () => b;
+
+  a &&= ++b;
+}).toThrow('"a" is read-only');
+expect(state4.getA()).toBe(1); // Assignment did not succeed
+expect(state4.getB()).toBe(2); // `++b` was evaluated before error thrown
+
+{
+  const a = 1;
+  let b = 1;
+  a ||= ++b;
+
+  expect(a).toBe(1); // Assignment not made
+  expect(b).toBe(1); // `++b` was not evaluated
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/assignment-expression/input.js

@@ -0,0 +1,7 @@
+const a = 5;
+let b = 0;
+a += b++;
+a >>>= b++;
+a ||= b++;
+a &&= b++;
+a ??= b++;

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/assignment-expression/output.js

@@ -0,0 +1,7 @@
+var a = 5;
+var b = 0;
+a + b++, babelHelpers.readOnlyError("a");
+a >>> b++, babelHelpers.readOnlyError("a");
+a || (b++, babelHelpers.readOnlyError("a"));
+a && (b++, babelHelpers.readOnlyError("a"));
+a ?? (b++, babelHelpers.readOnlyError("a"));

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/deadcode-violation/output.js

@@ -1,5 +1,5 @@
 (function () {
   var a = "foo";
-  if (false) a = (babelHelpers.readOnlyError("a"), "false");
+  if (false) "false", babelHelpers.readOnlyError("a");
   return a;
 })();

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/destructuring-assignment/output.js

@@ -1,3 +1,3 @@
 var a = 1,
     b = 2;
-a = (babelHelpers.readOnlyError("a"), 3);
+3, babelHelpers.readOnlyError("a");

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/loop/input.js

@@ -1,3 +1,7 @@
 for (const i = 0; i < 3; i = i + 1) {
   console.log(i);
 }
+
+for (const j = 0; j < 3; j++) {
+  console.log(j);
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/loop/output.js

@@ -1,3 +1,7 @@
-for (var i = 0; i < 3; i = (babelHelpers.readOnlyError("i"), i + 1)) {
+for (var i = 0; i < 3; i + 1, babelHelpers.readOnlyError("i")) {
   console.log(i);
 }
+
+for (var j = 0; j < 3; +j, babelHelpers.readOnlyError("j")) {
+  console.log(j);
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/nested-update-expressions/output.js

@@ -2,5 +2,5 @@ var c = 17;
 var a = 0;
 
 function f() {
-  return (babelHelpers.readOnlyError("c"), ++c) + --a;
+  return (+c, babelHelpers.readOnlyError("c")) + --a;
 }

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/no-assignment/exec.js

@@ -1,4 +1,20 @@
+const state1 = {};
 expect(function() {
   const a = 3;
+  state1.getA = () => a;
+
   a = 7;
 }).toThrow('"a" is read-only');
+expect(state1.getA()).toBe(3); // Assignment did not succeed
+
+const state2 = {};
+expect(function() {
+  const a = 3;
+  let b = 0;
+  state2.getA = () => a;
+  state2.getB = () => b;
+
+  a = b++;
+}).toThrow('"a" is read-only');
+expect(state2.getA()).toBe(3); // Assignment did not succeed
+expect(state2.getB()).toBe(1); // `b++` was evaluated before error thrown

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/no-assignment/input.js

@@ -1,3 +1,6 @@
 const MULTIPLIER = 5;
-
 MULTIPLIER = "overwrite";
+
+const a = 5;
+let b = 0;
+a = b++;

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/no-assignment/output.js

@@ -1,2 +1,5 @@
 var MULTIPLIER = 5;
-MULTIPLIER = (babelHelpers.readOnlyError("MULTIPLIER"), "overwrite");
+"overwrite", babelHelpers.readOnlyError("MULTIPLIER");
+var a = 5;
+var b = 0;
+b++, babelHelpers.readOnlyError("a");

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/no-for-in/exec.js

@@ -1,5 +1,8 @@
+const state = {};
 function f(arr) {
   const MULTIPLIER = 5;
+  state.getMultiplier = () => MULTIPLIER;
+
   for (MULTIPLIER in arr);
 
   return 'survived';
@@ -8,5 +11,6 @@ function f(arr) {
 expect(function() {
   f([1,2,3]);
 }).toThrow('"MULTIPLIER" is read-only');
+expect(state.getMultiplier()).toBe(5); // Assignment did not succeed
 
 expect(f([])).toBe('survived');

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/no-for-in/output.js

@@ -1,6 +1,6 @@
 var MULTIPLIER = 5;
 
-for (MULTIPLIER in arr) {
+for (var _MULTIPLIER in arr) {
   babelHelpers.readOnlyError("MULTIPLIER");
   ;
 }

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/update-expression-prefix/exec.js

@@ -1,4 +1,23 @@
+const state1 = {};
 expect(function() {
   const a = "str";
+  state1.getA = () => a;
+
   --a;
 }).toThrow('"a" is read-only');
+expect(state1.getA()).toBe("str"); // Assignment did not succeed
+
+const state2 = {};
+expect(function() {
+  const b = {
+    valueOf() {
+      state2.valueOfIsCalled = true;
+    }
+  };
+  state2.b = b;
+  state2.getB = () => b;
+
+  --b;
+}).toThrow('"b" is read-only');
+expect(state2.getB()).toBe(state2.b); // Assignment did not succeed
+expect(state2.valueOfIsCalled).toBe(true); // `bar` was read before error thrown

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/update-expression-prefix/output.js

@@ -1,2 +1,2 @@
 var a = "str";
-babelHelpers.readOnlyError("a"), --a;
++a, babelHelpers.readOnlyError("a");

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/update-expression/exec.js

@@ -1,4 +1,23 @@
+const state1 = {};
 expect(function() {
   const foo = 1;
+  state1.getFoo = () => foo;
+
   foo++;
 }).toThrow('"foo" is read-only');
+expect(state1.getFoo()).toBe(1); // Assignment did not succeed
+
+const state2 = {};
+expect(function() {
+  const bar = {
+    valueOf() {
+      state2.valueOfIsCalled = true;
+    }
+  };
+  state2.bar = bar;
+  state2.getBar = () => bar;
+
+  bar++;
+}).toThrow('"bar" is read-only');
+expect(state2.getBar()).toBe(state2.bar); // Assignment did not succeed
+expect(state2.valueOfIsCalled).toBe(true); // `bar` was read before error thrown

packages/babel-plugin-transform-block-scoping/test/fixtures/const-violations/update-expression/output.js

@@ -1,2 +1,2 @@
 var foo = 1;
-babelHelpers.readOnlyError("foo"), foo++;
++foo, babelHelpers.readOnlyError("foo");