Allow mixin classes to have members added via .prototype calls.

For example:

  /** @type {string} */
  MyMixin.prototype.foo;

We already support this behavior for normal classes, but not for mixin
classes.

packages/analyzer/src/javascript/class-scanner.ts

@@ -76,16 +76,16 @@ export class ClassScanner implements JavaScriptScanner {
       document: JavaScriptDocument,
       visit: (visitor: Visitor) => Promise<void>) {
     const classFinder = new ClassFinder(document);
-    const mixinFinder = new MixinVisitor(document);
     const elementDefinitionFinder =
         new CustomElementsDefineCallFinder(document);
     const prototypeMemberFinder = new PrototypeMemberFinder(document);
+    await visit(prototypeMemberFinder);
+    const mixinFinder = new MixinVisitor(document, prototypeMemberFinder);
     // Find all classes and all calls to customElements.define()
     await Promise.all([
       visit(classFinder),
       visit(elementDefinitionFinder),
       visit(mixinFinder),
-      visit(prototypeMemberFinder),
     ]);
     const mixins = mixinFinder.mixins;
 
@@ -424,7 +424,7 @@ interface CustomElementDefinition {
   definition?: ElementDefineCall;
 }
 
-class PrototypeMemberFinder implements Visitor {
+export class PrototypeMemberFinder implements Visitor {
   readonly members = new MapWithDefault<string, {
     methods: Map<string, ScannedMethod>,
     properties: Map<string, ScannedProperty>
@@ -505,16 +505,16 @@ class PrototypeMemberFinder implements Visitor {
     }
 
     if (jsdoc.hasTag(jsdocAnn, 'function')) {
-      const prop =
+      const method =
           this._createMethodFromExpression(node.property.name, node, jsdocAnn);
-      if (prop) {
-        this._addMethodToClass(cls, prop);
+      if (method) {
+        this._addMethodToClass(cls, method);
       }
     } else {
-      const method = this._createPropertyFromExpression(
+      const prop = this._createPropertyFromExpression(
           node.property.name, node, jsdocAnn);
-      if (method) {
-        this._addPropertyToClass(cls, method);
+      if (prop) {
+        this._addPropertyToClass(cls, prop);
       }
     }
   }

packages/analyzer/src/polymer/polymer2-mixin-scanner.ts

@@ -16,7 +16,7 @@ import {NodePath} from '@babel/traverse';
 import * as babel from '@babel/types';
 
 import {getIdentifierName, getNamespacedIdentifier} from '../javascript/ast-value';
-import {extractPropertiesFromClass} from '../javascript/class-scanner';
+import {extractPropertiesFromClass, PrototypeMemberFinder} from '../javascript/class-scanner';
 import {Visitor} from '../javascript/estree-visitor';
 import * as esutil from '../javascript/esutil';
 import {getMethods, getOrInferPrivacy, getStaticMethods} from '../javascript/esutil';
@@ -34,10 +34,14 @@ export class MixinVisitor implements Visitor {
   private _currentMixin: ScannedPolymerElementMixin|null = null;
   private _currentMixinNode: babel.Node|null = null;
   private _currentMixinFunction: babel.Function|null = null;
+  private _prototypeMemberFinder: PrototypeMemberFinder;
   readonly warnings: Warning[] = [];
 
-  constructor(document: JavaScriptDocument) {
+  constructor(
+      document: JavaScriptDocument,
+      prototypeMemberFinder: PrototypeMemberFinder) {
     this._document = document;
+    this._prototypeMemberFinder = prototypeMemberFinder;
   }
 
   enterAssignmentExpression(
@@ -159,7 +163,21 @@ export class MixinVisitor implements Visitor {
     mixin.events = esutil.getEventComments(node);
     // mixin.sourceRange = this._document.sourceRangeForNode(node);
 
-    return mixin;
+    // Also add members that were described like:
+    //   /** @type {string} */
+    //   MixinClass.prototype.foo;
+    const name = getIdentifierName(node.id);
+    if (name !== undefined) {
+      const prototypeMembers = this._prototypeMemberFinder.members.get(name);
+      if (prototypeMembers !== undefined) {
+        for (const [, property] of prototypeMembers.properties) {
+          mixin.addProperty(property);
+        }
+        for (const [, method] of prototypeMembers.methods) {
+          mixin.addMethod(method);
+        }
+      }
+    }
   }
 }
 

packages/gen-typescript-declarations/src/test/goldens/polymer-2/lib/legacy/legacy-element-mixin.d.ts

@@ -46,6 +46,7 @@ declare namespace Polymer {
      * `this.getRootNode().host`.
      */
     readonly domHost: any;
+    is: string;
 
     /**
      * Overrides the default `Polymer.PropertyEffects` implementation to

packages/gen-typescript-declarations/src/test/goldens/polymer-3/lib/legacy/legacy-element-mixin.d.ts

@@ -71,6 +71,7 @@ interface LegacyElementMixin extends ElementMixin, PropertyEffects, TemplateStam
    * `this.getRootNode().host`.
    */
   readonly domHost: any;
+  is: string;
 
   /**
    * Overrides the default `Polymer.PropertyEffects` implementation to

packages/gen-typescript-declarations/src/test/goldens_goog/polymer-2/lib/legacy/legacy-element-mixin.d.ts

@@ -46,6 +46,7 @@ declare namespace Polymer {
      * `this.getRootNode().host`.
      */
     readonly domHost: any;
+    is: string;
 
     /**
      * Overrides the default `Polymer.PropertyEffects` implementation to

packages/gen-typescript-declarations/src/test/goldens_goog/polymer-3/lib/legacy/legacy-element-mixin.d.ts

@@ -73,6 +73,7 @@ declare module 'goog:polymer.polymer.lib.legacy.legacyElementMixin' {
      * `this.getRootNode().host`.
      */
     readonly domHost: any;
+    is: string;
 
     /**
      * Overrides the default `Polymer.PropertyEffects` implementation to