Allow compiling #foo in obj without compiling private fields

packages/babel-plugin-proposal-private-property-in-object/package.json

@@ -18,7 +18,8 @@
   ],
   "dependencies": {
     "@babel/helper-create-class-features-plugin": "workspace:^7.13.0",
-    "@babel/helper-plugin-utils": "workspace:^7.13.0"
+    "@babel/helper-plugin-utils": "workspace:^7.13.0",
+    "@babel/plugin-syntax-private-property-in-object": "workspace:^7.13.0"
   },
   "peerDependencies": {
     "@babel/core": "^7.0.0-0"

packages/babel-plugin-proposal-private-property-in-object/src/index.js

@@ -6,15 +6,21 @@ import {
   FEATURES,
 } from "@babel/helper-create-class-features-plugin";
 
+import pluginPrivateIn from "./native-private-fields";
+
 export default declare((api, options) => {
   api.assertVersion(7);
 
+  const { loose, nativePrivateFields } = options;
+
+  if (nativePrivateFields) return pluginPrivateIn(api);
+
   return createClassFeaturePlugin({
     name: "proposal-class-properties",
 
     api,
     feature: FEATURES.privateIn,
-    loose: options.loose,
+    loose,
 
     manipulateOptions(opts, parserOpts) {
       parserOpts.plugins.push("privateIn");

packages/babel-plugin-proposal-private-property-in-object/src/native-private-fields.js

@@ -0,0 +1,112 @@
+import syntaxPlugin from "@babel/plugin-syntax-private-property-in-object";
+import { injectInitialization as injectConstructorInit } from "@babel/helper-create-class-features-plugin";
+
+export default function pluginPrivateIn({ types: t, template }) {
+  const ids = new WeakMap();
+
+  function unshadow(name, targetScope, scope) {
+    while (scope !== targetScope) {
+      if (scope.hasOwnBinding(name)) scope.rename(name);
+      scope = scope.parent;
+    }
+  }
+
+  function injectInitialization(classPath, init) {
+    let firstFieldPath;
+    let consturctorPath;
+
+    for (const el of classPath.get("body.body")) {
+      if (
+        (el.isClassProperty() || el.isClassPrivateProperty()) &&
+        !el.node.static
+      ) {
+        firstFieldPath = el;
+        break;
+      }
+      if (!consturctorPath && el.isClassMethod({ kind: "constructor" })) {
+        consturctorPath = el;
+      }
+    }
+
+    if (firstFieldPath) {
+      if (firstFieldPath.node.value) {
+        firstFieldPath.set(
+          "value",
+          t.sequenceExpression([init, firstFieldPath.node.value]),
+        );
+      } else {
+        firstFieldPath.set("value", t.unaryExpression("void", init));
+      }
+    } else {
+      injectConstructorInit(classPath, consturctorPath, [
+        t.expressionStatement(init),
+      ]);
+    }
+  }
+
+  return {
+    name: "proposal-private-property-in-object",
+    inherits: syntaxPlugin,
+    visitor: {
+      BinaryExpression(path) {
+        const { node } = path;
+        if (node.operator !== "in") return;
+        if (!t.isPrivateName(node.left)) return;
+
+        const { name } = node.left.id;
+
+        let isStatic;
+        const outerClass = path.findParent(path => {
+          if (!path.isClass()) return false;
+
+          const privateElement = path.node.body.body.find(
+            node => t.isPrivate(node) && node.key.id.name === name,
+          );
+          if (!privateElement) return false;
+
+          isStatic = privateElement.static;
+          return true;
+        });
+
+        if (outerClass.parentPath.scope.path.isPattern()) {
+          outerClass.replaceWith(template.ast`(() => ${outerClass.node})()`);
+          // The injected class will be queued and eventually transformed when visited
+          return;
+        }
+
+        if (isStatic) {
+          if (outerClass.node.id) {
+            unshadow(outerClass.node.id.name, outerClass.scope, path.scope);
+          } else {
+            outerClass.set("id", path.scope.generateUidIdentifier("class"));
+          }
+          path.replaceWith(
+            template.expression.ast`
+              ${t.cloneNode(outerClass.node.id)} === ${path.node.right}
+            `,
+          );
+          return;
+        }
+
+        let id = ids.get(outerClass.node);
+        if (!id) {
+          id = outerClass.scope.generateUidIdentifier(
+            `${outerClass.node.id?.name || ""} brandCheck`,
+          );
+          ids.set(outerClass.node, id);
+
+          injectInitialization(
+            outerClass,
+            template.expression.ast`${t.cloneNode(id)}.add(this)`,
+          );
+
+          outerClass.insertBefore(template.ast`var ${id} = new WeakSet()`);
+        }
+
+        path.replaceWith(
+          template.expression.ast`${t.cloneNode(id)}.has(${path.node.right})`,
+        );
+      },
+    },
+  };
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/input.js

@@ -0,0 +1,7 @@
+class Foo {
+  get #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/accessor/output.js

@@ -0,0 +1,14 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  get #foo() {}
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-in-default-param/input.js

@@ -0,0 +1,4 @@
+(x = class {
+  #foo;
+  test(other) { return #foo in other }
+}) => {}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-in-default-param/output.js

@@ -0,0 +1,12 @@
+(x = (() => {
+  var _brandCheck;
+
+  return _brandCheck = new WeakSet(), class {
+    #foo = void _brandCheck.add(this);
+
+    test(other) {
+      return _brandCheck.has(other);
+    }
+
+  };
+})()) => {};

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/input.js

@@ -0,0 +1,9 @@
+function fn() {
+  return new class {
+    #priv;
+
+    method(obj) {
+      return #priv in obj;
+    }
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-instance/output.js

@@ -0,0 +1,12 @@
+function fn() {
+  var _brandCheck;
+
+  return new (_brandCheck = new WeakSet(), class {
+    #priv = void _brandCheck.add(this);
+
+    method(obj) {
+      return _brandCheck.has(obj);
+    }
+
+  })();
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/input.js

@@ -0,0 +1,9 @@
+function fn() {
+  return new class {
+    static #priv;
+
+    method(obj) {
+      return #priv in obj;
+    }
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/class-expression-static/output.js

@@ -0,0 +1,10 @@
+function fn() {
+  return new class _class {
+    static #priv;
+
+    method(obj) {
+      return _class === obj;
+    }
+
+  }();
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/input.js

@@ -0,0 +1,7 @@
+class Foo {
+  #foo = 1;
+
+  test(other) {
+    return #foo in other;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/field/output.js

@@ -0,0 +1,10 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  #foo = (_FooBrandCheck.add(this), 1);
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/input.js

@@ -0,0 +1,7 @@
+class Foo {
+  #foo() {}
+
+  test(other) {
+    return #foo in other;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/method/output.js

@@ -0,0 +1,14 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  constructor() {
+    _FooBrandCheck.add(this);
+  }
+
+  #foo() {}
+
+  test(other) {
+    return _FooBrandCheck.has(other);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/input.js

@@ -0,0 +1,18 @@
+class Foo {
+  #foo = 1;
+  #bar = 1;
+
+  test() {
+    class Nested {
+      #bar = 2;
+
+      test() {
+        #foo in this;
+        #bar in this;
+      }
+    }
+
+    #foo in this;
+    #bar in this;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-other-redeclared/output.js

@@ -0,0 +1,26 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  #foo = (_FooBrandCheck.add(this), 1);
+  #bar = 1;
+
+  test() {
+    var _NestedBrandCheck = new WeakSet();
+
+    class Nested {
+      #bar = (_NestedBrandCheck.add(this), 2);
+
+      test() {
+        _FooBrandCheck.has(this);
+
+        _NestedBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+
+    _FooBrandCheck.has(this);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/input.js

@@ -0,0 +1,15 @@
+class Foo {
+  #foo = 1;
+
+  test() {
+    class Nested {
+      #foo = 2;
+
+      test() {
+        #foo in this;
+      }
+    }
+
+    #foo in this;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class-redeclared/output.js

@@ -0,0 +1,21 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  #foo = (_FooBrandCheck.add(this), 1);
+
+  test() {
+    var _NestedBrandCheck = new WeakSet();
+
+    class Nested {
+      #foo = (_NestedBrandCheck.add(this), 2);
+
+      test() {
+        _NestedBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/input.js

@@ -0,0 +1,13 @@
+class Foo {
+  #foo = 1;
+
+  test() {
+    class Nested {
+      test() {
+        #foo in this;
+      }
+    }
+
+    #foo in this;
+  }
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/nested-class/output.js

@@ -0,0 +1,17 @@
+var _FooBrandCheck = new WeakSet();
+
+class Foo {
+  #foo = (_FooBrandCheck.add(this), 1);
+
+  test() {
+    class Nested {
+      test() {
+        _FooBrandCheck.has(this);
+      }
+
+    }
+
+    _FooBrandCheck.has(this);
+  }
+
+}

packages/babel-plugin-proposal-private-property-in-object/test/fixtures/to-native-fields/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["proposal-private-property-in-object", { "nativePrivateFields": true }],
+    "syntax-class-properties"
+  ]
+}