Define readOnlyError helper and use in check-constants plugin

packages/babel-helpers/src/helpers.js

@@ -627,6 +627,12 @@ helpers.temporalRef = defineHelper(`
   }
 `);
 
+helpers.readOnlyError = defineHelper(`
+  export default function _readOnlyError(name) {
+    throw new Error("\\"" + name + "\\" is read-only");
+  }
+`);
+
 helpers.temporalUndefined = defineHelper(`
   export default {};
 `);

packages/babel-plugin-check-constants/src/index.js

@@ -1,50 +1,37 @@
 import { types as t } from "@babel/core";
 
 export default function() {
-  /**
-   * Helper function to run a statement before an expression by replacing it with a comma expression
-   * and wrapping the statement in an IIFE as the first operand.
-   */
-  function statementBeforeExpression(statement, expression) {
-    return t.sequenceExpression([
-      t.callExpression(
-        t.functionExpression(null, [], t.blockStatement([statement])),
-        [],
-      ),
-      expression,
-    ]);
-  }
-
   return {
     visitor: {
-      Scope({ scope }) {
+      Scope({ scope }, state) {
         for (const name in scope.bindings) {
           const binding = scope.bindings[name];
           if (binding.kind !== "const") continue;
 
           for (const violation of (binding.constantViolations: Array)) {
-            const throwNode = t.throwStatement(
+            const readOnlyError = state.addHelper("readOnlyError");
-              t.newExpression(t.identifier("Error"), [
+            const throwNode = t.callExpression(readOnlyError, [
-                t.stringLiteral(`"${name}" is read-only`),
+              t.stringLiteral(name),
-              ]),
+            ]);
-            );
 
             if (violation.isAssignmentExpression()) {
               violation
                 .get("right")
                 .replaceWith(
-                  statementBeforeExpression(
+                  t.sequenceExpression([
                     throwNode,
                     violation.get("right").node,
-                  ),
+                  ]),
                 );
             } else if (violation.isUpdateExpression()) {
               violation.replaceWith(
-                statementBeforeExpression(throwNode, violation.node),
+                t.sequenceExpression([throwNode, violation.node]),
               );
             } else if (violation.isForXStatement()) {
               violation.ensureBlock();
-              violation.node.body.body.unshift(throwNode);
+              violation.node.body.body.unshift(
+                t.expressionStatement(throwNode),
+              );
             }
           }
         }

packages/babel-plugin-check-constants/test/fixtures/general/deadcode-violation/expected.js

@@ -1,7 +1,7 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 (function () {
   var a = "foo";
-  if (false) a = (function () {
+  if (false) a = (_readOnlyError("a"), "false");
-    throw new Error("\"a\" is read-only");
-  }(), "false");
   return a;
 })();

packages/babel-plugin-check-constants/test/fixtures/general/destructuring-assignment/expected.js

@@ -1,5 +1,5 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var a = 1,
     b = 2;
-a = (function () {
+a = (_readOnlyError("a"), 3);
-  throw new Error("\"a\" is read-only");
-}(), 3);

packages/babel-plugin-check-constants/test/fixtures/general/loop/expected.js

@@ -1,5 +1,5 @@
-for (var i = 0; i < 3; i = (function () {
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
-  throw new Error("\"i\" is read-only");
+
-}(), i + 1)) {
+for (var i = 0; i < 3; i = (_readOnlyError("i"), i + 1)) {
   console.log(i);
 }

packages/babel-plugin-check-constants/test/fixtures/general/nested-update-expressions/expected.js

@@ -1,8 +1,8 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var c = 17;
 var a = 0;
 
 function f() {
-  return (function () {
+  return (_readOnlyError("c"), ++c) + --a;
-    throw new Error("\"c\" is read-only");
-  }(), ++c) + --a;
 }

packages/babel-plugin-check-constants/test/fixtures/general/no-assignment/expected.js

@@ -1,4 +1,4 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var MULTIPLIER = 5;
-MULTIPLIER = (function () {
+MULTIPLIER = (_readOnlyError("MULTIPLIER"), "overwrite");
-  throw new Error("\"MULTIPLIER\" is read-only");
-}(), "overwrite");

packages/babel-plugin-check-constants/test/fixtures/general/no-for-in/expected.js

@@ -1,6 +1,9 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var MULTIPLIER = 5;
 
 for (MULTIPLIER in arr) {
-  throw new Error("\"MULTIPLIER\" is read-only");
+  _readOnlyError("MULTIPLIER");
+
   ;
 }

packages/babel-plugin-check-constants/test/fixtures/general/update-expression-prefix/expected.js

@@ -1,4 +1,4 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var a = "str";
-(function () {
+_readOnlyError("a"), --a;
-  throw new Error("\"a\" is read-only");
-})(), --a;

packages/babel-plugin-check-constants/test/fixtures/general/update-expression/expected.js

@@ -1,4 +1,4 @@
+function _readOnlyError(name) { throw new Error("\"" + name + "\" is read-only"); }
+
 var foo = 1;
-(function () {
+_readOnlyError("foo"), foo++;
-  throw new Error("\"foo\" is read-only");
-})(), foo++;