Fix tdz checks in transform-block-scoping plugin (#9498)

* Better tdz tests

- Use jest's expect.toThrow/expect.not.toThrow
- Add input/output tests

* Fix basic tdz (a = 2; let a)

Fixes #6848

* Make _guessExecutionStatusRelativeTo more robust

* Add tests

* Return less "unkown" execution status

* "function" execution status does not exist

* Fix recursive functions

* Update helper version

* "finally" blocks are always executed

* Typo

packages/babel-helpers/src/helpers.js

@@ -817,18 +817,6 @@ helpers.taggedTemplateLiteralLoose = helper("7.0.0-beta.0")`
   }
 `;
 
-helpers.temporalRef = helper("7.0.0-beta.0")`
-  import undef from "temporalUndefined";
-
-  export default function _temporalRef(val, name) {
-    if (val === undef) {
-      throw new ReferenceError(name + " is not defined - temporal dead zone");
-    } else {
-      return val;
-    }
-  }
-`;
-
 helpers.readOnlyError = helper("7.0.0-beta.0")`
   export default function _readOnlyError(name) {
     throw new Error("\\"" + name + "\\" is read-only");
@@ -842,7 +830,24 @@ helpers.classNameTDZError = helper("7.0.0-beta.0")`
 `;
 
 helpers.temporalUndefined = helper("7.0.0-beta.0")`
-  export default {};
+  // This function isn't mean to be called, but to be used as a reference.
+  // We can't use a normal object because it isn't hoisted.
+  export default function _temporalUndefined() {}
+`;
+
+helpers.tdz = helper("7.5.5")`
+  export default function _tdzError(name) {
+    throw new ReferenceError(name + " is not defined - temporal dead zone");
+  }
+`;
+
+helpers.temporalRef = helper("7.0.0-beta.0")`
+  import undef from "temporalUndefined";
+  import err from "tdz";
+
+  export default function _temporalRef(val, name) {
+    return val === undef ? err(name) : val;
+  }
 `;
 
 helpers.slicedToArray = helper("7.0.0-beta.0")`

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

@@ -16,7 +16,7 @@ export default declare((api, opts) => {
     throw new Error(`.throwIfClosureRequired must be a boolean, or undefined`);
   }
   if (typeof tdzEnabled !== "boolean") {
-    throw new Error(`.throwIfClosureRequired must be a boolean, or undefined`);
+    throw new Error(`.tdz must be a boolean, or undefined`);
   }
 
   return {
@@ -33,11 +33,13 @@ export default declare((api, opts) => {
 
           for (let i = 0; i < node.declarations.length; i++) {
             const decl = node.declarations[i];
-            if (decl.init) {
-              const assign = t.assignmentExpression("=", decl.id, decl.init);
-              assign._ignoreBlockScopingTDZ = true;
-              nodes.push(t.expressionStatement(assign));
-            }
+            const assign = t.assignmentExpression(
+              "=",
+              decl.id,
+              decl.init || scope.buildUndefinedNode(),
+            );
+            assign._ignoreBlockScopingTDZ = true;
+            nodes.push(t.expressionStatement(assign));
             decl.init = this.addHelper("temporalUndefined");
           }
 
@@ -181,6 +183,8 @@ const letReferenceBlockVisitor = traverse.visitors.merge([
       // simply rename the variables.
       if (state.loopDepth > 0) {
         path.traverse(letReferenceFunctionVisitor, state);
+      } else {
+        path.traverse(tdzVisitor, state);
       }
       return path.skip();
     },
@@ -756,7 +760,7 @@ class BlockScoping {
       closurify: false,
       loopDepth: 0,
       tdzEnabled: this.tdzEnabled,
-      addHelper: name => this.addHelper(name),
+      addHelper: name => this.state.addHelper(name),
     };
 
     if (isInLoop(this.blockPath)) {

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

@@ -1,12 +1,12 @@
-import { types as t } from "@babel/core";
+import { types as t, template } from "@babel/core";
 
 function getTDZStatus(refPath, bindingPath) {
   const executionStatus = bindingPath._guessExecutionStatusRelativeTo(refPath);
 
   if (executionStatus === "before") {
-    return "inside";
-  } else if (executionStatus === "after") {
     return "outside";
+  } else if (executionStatus === "after") {
+    return "inside";
   } else {
     return "maybe";
   }
@@ -41,7 +41,7 @@ export const visitor = {
     if (bindingPath.isFunctionDeclaration()) return;
 
     const status = getTDZStatus(path, bindingPath);
-    if (status === "inside") return;
+    if (status === "outside") return;
 
     if (status === "maybe") {
       const assert = buildTDZAssert(node, state);
@@ -57,19 +57,8 @@ export const visitor = {
       } else {
         path.replaceWith(assert);
       }
-    } else if (status === "outside") {
-      path.replaceWith(
-        t.throwStatement(
-          t.inherits(
-            t.newExpression(t.identifier("ReferenceError"), [
-              t.stringLiteral(
-                `${node.name} is not defined - temporal dead zone`,
-              ),
-            ]),
-            node,
-          ),
-        ),
-      );
+    } else if (status === "inside") {
+      path.replaceWith(template.ast`${state.addHelper("tdz")}("${node.name}")`);
     }
   },
 
@@ -87,14 +76,14 @@ export const visitor = {
         const id = ids[name];
 
         if (isReference(id, path.scope, state)) {
-          nodes.push(buildTDZAssert(id, state));
+          nodes.push(id);
         }
       }
 
       if (nodes.length) {
         node._ignoreBlockScopingTDZ = true;
         nodes.push(node);
-        path.replaceWithMultiple(nodes.map(t.expressionStatement));
+        path.replaceWithMultiple(nodes.map(n => t.expressionStatement(n)));
       }
     },
   },

packages/babel-plugin-transform-block-scoping/test/fixtures/exec/scope-bindings.js

@@ -5,6 +5,7 @@ if (x) {
 
 var innerScope = true;
 var res = transform(code, {
+  configFile: false,
   plugins: opts.plugins.concat([
     function (b) {
       var t = b.types;
@@ -34,3 +35,4 @@ if (x) {
 }`;
 
 expect(res.code).toBe(expected);
+expect(innerScope).toBe(false);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/block-ref-function-call/exec.js

@@ -1,3 +1,5 @@
-f();
+expect(() => {
+  f();
 
-const f = function f() {}
+  const f = function f() {}
+}).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/block-ref-function-call/input.js

@@ -0,0 +1,3 @@
+f();
+
+const f = function f() {}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/block-ref-function-call/output.js

@@ -0,0 +1,3 @@
+babelHelpers.tdz("f")();
+
+var f = function f() {};

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/destructured-self-reference/exec.js

@@ -1 +1,3 @@
-let { b: d } = { d }
+expect(() => {
+  let { b: d } = { d }
+}).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/destructured-self-reference/input.js

@@ -0,0 +1 @@
+let { b: d } = { d }

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/destructured-self-reference/output.js

@@ -0,0 +1,5 @@
+var {
+  b: d
+} = {
+  d: babelHelpers.tdz("d")
+};

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-after/exec.js

@@ -0,0 +1,7 @@
+expect(() => {
+  function f() {
+    x;
+  }
+  let x;
+  f();
+}).not.toThrow();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-after/output.js

@@ -0,0 +1,6 @@
+function f() {
+  x;
+}
+
+var x;
+f();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-before/exec.js

@@ -0,0 +1,7 @@
+expect(() => {
+  function f() {
+    x;
+  }
+  f();
+  let x;
+}).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-before/input.js

@@ -0,0 +1,5 @@
+function f() {
+    x;
+}
+f();
+let x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-before/output.js

@@ -0,0 +1,6 @@
+function f() {
+  babelHelpers.tdz("x");
+}
+
+f();
+var x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-real-after/exec.js

@@ -0,0 +1,6 @@
+expect(() => {
+  function f() { x }
+  Math.random() === 2 && f();
+  let x;
+  f();
+}).not.toThrow();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-real-after/input.js

@@ -0,0 +1,4 @@
+function f() { x }
+Math.random() === 2 && f();
+let x;
+f();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-real-after/output.js

@@ -0,0 +1,9 @@
+var x = babelHelpers.temporalUndefined;
+
+function f() {
+  babelHelpers.temporalRef(x, "x");
+}
+
+Math.random() === 2 && f();
+x = void 0;
+f();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-value-assign/exec.js

@@ -0,0 +1,5 @@
+function f() { x }
+Math.random() === 2 && f();
+let x = 3;
+
+expect(x).toBe(3);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-value-assign/input.js

@@ -0,0 +1,5 @@
+function f() { x }
+Math.random() === 2 && f();
+let x = 3;
+
+expect(x).toBe(3);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe-value-assign/output.js

@@ -0,0 +1,9 @@
+var x = babelHelpers.temporalUndefined;
+
+function f() {
+  babelHelpers.temporalRef(x, "x");
+}
+
+Math.random() === 2 && f();
+x = 3;
+expect(x).toBe(3);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe/exec.js

@@ -0,0 +1,29 @@
+// "random" :)
+let random = (i => {
+  const vals = [0, 0, 1, 1];
+  return () => vals[i++];
+})(0);
+
+expect(() => {
+  function f() { x }
+  random() && f();
+  let x;
+}).not.toThrow();
+
+expect(() => {
+  function f() { x }
+  random() || f();
+  let x;
+}).toThrow(ReferenceError);
+
+expect(() => {
+  function f() { x }
+  random() && f();
+  let x;
+}).toThrow(ReferenceError);
+
+expect(() => {
+  function f() { x }
+  random() || f();
+  let x;
+}).not.toThrow();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe/input.js

@@ -0,0 +1,3 @@
+function f() { x }
+Math.random() && f();
+let x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-maybe/output.js

@@ -0,0 +1,9 @@
+var x = babelHelpers.temporalUndefined;
+
+function f() {
+  babelHelpers.temporalRef(x, "x");
+}
+
+Math.random() && f();
+x = void 0;
+void 0;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-nested-function/exec.js

@@ -0,0 +1,17 @@
+expect(() => {
+  function f() {
+    return function() { x };
+  }
+  let g = f();
+  let x;
+  g();
+}).not.toThrow();
+
+expect(() => {
+  function f() {
+    return function() { x };
+  }
+  let g = f();
+  g();
+  let x;
+}).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-nested-function/input.js

@@ -0,0 +1,5 @@
+function f() {
+  return function() { x };
+}
+f();
+let x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-nested-function/output.js

@@ -0,0 +1,11 @@
+var x = babelHelpers.temporalUndefined;
+
+function f() {
+  return function () {
+    babelHelpers.temporalRef(x, "x");
+  };
+}
+
+f();
+x = void 0;
+void 0;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-recursive-after/exec.js

@@ -0,0 +1,9 @@
+expect(() => {
+  function f(i) {
+    if (i) f(i - 1);
+    x;
+  }
+
+  let x;
+  f(3);
+}).not.toThrow();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-recursive-after/input.js

@@ -0,0 +1,7 @@
+function f(i) {
+  if (i) f(i - 1);
+  x;
+}
+
+let x;
+f(3);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-recursive-after/output.js

@@ -0,0 +1,7 @@
+function f(i) {
+  if (i) f(i - 1);
+  x;
+}
+
+var x;
+f(3);