Review by JLHwung

packages/babel-plugin-transform-block-scoping/src/annex-B_3_3.ts

@@ -51,6 +51,8 @@ export const annexB33FunctionsVisitor: Visitor = {
 function transformStatementList(paths: NodePath<t.Statement>[]) {
   outer: for (const path of paths) {
     if (!path.isFunctionDeclaration()) continue;
+    // Annex B.3.3 only applies to plain functions.
+    if (path.node.async || path.node.generator) return;
 
     const { scope } = path.parentPath;
     if (isVarScope(scope)) return;
@@ -74,9 +76,6 @@ function maybeTransformBlockScopedFunction(
     parentPath: { scope },
   } = path;
 
-  // Annex B.3.3 only applies to plain functions.
-  if (node.async || node.generator) return;
-
   const { id } = node;
   scope.removeOwnBinding(id.name);
   node.id = null;
@@ -115,7 +114,11 @@ function isStrict(path: NodePath) {
   return !!path.find(({ node }) => {
     if (t.isProgram(node)) {
       if (node.sourceType === "module") return true;
-    } else if (!t.isBlockStatement(node)) return false;
+    } else if (t.isClass(node)) {
+      return true;
+    } else if (!t.isBlockStatement(node)) {
+      return false;
+    }
 
     return node.directives?.some(
       directive => directive.value.value === "use strict",

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

@@ -93,7 +93,7 @@ export default declare((api, opts: Options) => {
 
             if (headPath?.isVariableDeclaration<t.Node>()) {
               // If we wrap the loop body, we transform the var
-              // declaration in the loop head now, to avoid having
+              // declaration in the loop head now, to avoid
               // invalid references that break other plugins:
               //
               //  for (let head of x) {

packages/babel-plugin-transform-block-scoping/src/loop.ts

@@ -75,7 +75,7 @@ function relativeLoopLocation(path: NodePath, loopPath: NodePath<t.Loop>) {
   let inClosure = false;
 
   for (let currPath = path; currPath; currPath = currPath.parentPath) {
-    if (currPath.isFunction()) inClosure = true;
+    if (currPath.isFunction() || currPath.isClass()) inClosure = true;
     if (currPath === bodyPath) {
       return { inBody: true, inClosure };
     } else if (currPath === loopPath) {

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-class/exec.js

@@ -0,0 +1,17 @@
+class A {
+  m() {
+    if (true) {
+      function f() {
+        return true;
+      }
+    }
+
+    function g() {
+      return f();
+    }
+
+    return g();
+  }
+}
+
+expect(new A().m).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-class/input.js

@@ -0,0 +1,17 @@
+class A {
+  m() {
+    if (true) {
+      function f() {
+        return true;
+      }
+    }
+
+    function g() {
+      return f();
+    }
+
+    return g();
+  }
+}
+
+expect(new A().m).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-class/output.js

@@ -0,0 +1,14 @@
+class A {
+  m() {
+    if (true) {
+      var _f = function () {
+        return true;
+      };
+    }
+    function g() {
+      return f();
+    }
+    return g();
+  }
+}
+expect(new A().m).toThrow(ReferenceError);

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-module-expression/input.js

@@ -0,0 +1,11 @@
+const m = module {
+  if (true) {
+    function f() {
+      return true;
+    }
+  }
+
+  function g() {
+    return f();
+  }
+};

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-module-expression/options.json

@@ -0,0 +1,7 @@
+{
+  "plugins": [
+    "transform-block-scoping",
+    "transform-block-scoped-functions",
+    "syntax-module-blocks"
+  ]
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/annex-B_3_3-in-module-expression/output.js

@@ -0,0 +1,10 @@
+var m = module {
+  if (true) {
+    var _f = function () {
+      return true;
+    };
+  }
+  function g() {
+    return f();
+  }
+};

packages/babel-plugin-transform-block-scoping/test/fixtures/general/loop-closure-in-class/exec.js

@@ -0,0 +1,10 @@
+let run = [];
+
+for (let i = 0; i < 2; i++) {
+  run.push(class C {
+    x = i;
+  });
+}
+
+expect(new run[0]().x).toBe(0);
+expect(new run[1]().x).toBe(1);

packages/babel-plugin-transform-block-scoping/test/fixtures/general/loop-closure-in-class/input.js

@@ -0,0 +1,5 @@
+for (let i = 0; i < 2; i++) {
+  class C {
+    x = i;
+  }
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/loop-closure-in-class/output.js

@@ -0,0 +1,8 @@
+var _loop = function (i) {
+  class C {
+    x = i;
+  }
+};
+for (var i = 0; i < 2; i++) {
+  _loop(i);
+}