Add @constructor JSDoc when extracting classes.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=215825326

src/com/google/javascript/jscomp/Es6ExtractClasses.java

@@ -189,13 +189,64 @@ private void extractClass(NodeTraversal t, Node classNode, Node parent) {
     Node statement = NodeUtil.getEnclosingStatement(parent);
     JSType classType = classNode.getJSType();
     checkState(!compiler.hasTypeCheckingRun() || classType != null);
-    Node className = IR.name(name).setJSType(classType);
-    parent.replaceChild(classNode, className.cloneTree());
+    // class name node used as LHS in newly created assignment
+    Node classNameLhs = IR.name(name).setJSType(classType);
+    // class name node that replaces the class literal in the original statement
+    Node classNameRhs = classNameLhs.cloneTree();
+    parent.replaceChild(classNode, classNameRhs);
     Node classDeclaration =
-        IR.constNode(className, classNode).useSourceInfoIfMissingFromForTree(classNode);
+        IR.constNode(classNameLhs, classNode).useSourceInfoIfMissingFromForTree(classNode);
     NodeUtil.addFeatureToScript(t.getCurrentFile(), Feature.CONST_DECLARATIONS);
     classDeclaration.setJSDocInfo(JSDocInfoBuilder.maybeCopyFrom(info).build());
     statement.getParent().addChildBefore(classDeclaration, statement);
+
+    // If the original statement was a variable declaration or qualified name assignment like
+    // like these:
+    // var ClassName = class {...
+    // OR
+    // some.qname.ClassName = class {...
+    //
+    // We will have changed the original statement to
+    //
+    // var ClassName = generatedName;
+    // OR
+    // some.qname.ClassName = generatedName;
+    //
+    // This is creating a type alias for a class, but since there's no literal class on the RHS,
+    // it doesn't look like one. Add at-constructor JSDoc to make it clear that this is happening.
+    //
+    // This was added to fix a specific problem where the original definition was for an abstract
+    // class, so its JSDoc included at-abstract.
+    // This caused ClosureCodeRemoval to think this rewritten assignment was a removable abstract
+    // method definition instead of the definition of an abstract class.
+    //
+    // TODO(b/117292942): Make ClosureCodeRemoval smarter so this hack isn't necessary to
+    // prevent incorrect removal of assignments.
+    if (NodeUtil.isNameDeclaration(statement)
+        && statement.hasOneChild()
+        && statement.getOnlyChild() == parent) {
+      // var ClassName = generatedName;
+      addAtConstructor(statement);
+    } else if (statement.isExprResult()) {
+      Node expr = statement.getOnlyChild();
+      if (expr.isAssign()
+          && expr.getFirstChild().isQualifiedName()
+          && expr.getSecondChild() == classNameRhs) {
+        // some.qname.ClassName = generatedName;
+        addAtConstructor(expr);
+      }
+    }
     compiler.reportChangeToEnclosingScope(classDeclaration);
   }
+
+  /**
+   * Add at-constructor to the JSDoc of the given node.
+   *
+   * @param node
+   */
+  private void addAtConstructor(Node node) {
+    JSDocInfoBuilder builder = JSDocInfoBuilder.maybeCopyFrom(node.getJSDocInfo());
+    builder.recordConstructor();
+    node.setJSDocInfo(builder.build());
+  }
 }

test/com/google/javascript/jscomp/Es6ExtractClassesTest.java

@@ -62,6 +62,7 @@ public void testSelfReference1() {
             "const testcode$classdecl$var0 = class {",
             "  constructor() { alert(testcode$classdecl$var0); }",
             "};",
+            "/** @constructor */",
             "var Outer=testcode$classdecl$var0"));
 
     test(
@@ -70,6 +71,7 @@ public void testSelfReference1() {
             "const testcode$classdecl$var0 = class {",
             "  constructor() { alert(testcode$classdecl$var0); }",
             "};",
+            "/** @constructor */",
             "let Outer=testcode$classdecl$var0"));
 
     test(
@@ -78,6 +80,7 @@ public void testSelfReference1() {
             "const testcode$classdecl$var0 = class {",
             "  constructor() { alert(testcode$classdecl$var0); }",
             "};",
+            "/** @constructor */",
             "const Outer=testcode$classdecl$var0"));
   }
 
@@ -118,7 +121,11 @@ public void testSelfReference_googModule() {
             "/** @const */ const testcode$classdecl$var0=class {",
             "  constructor(){ alert(testcode$classdecl$var0); }",
             "};",
-            "/** @const */ var module$exports$example=testcode$classdecl$var0"));
+            "/**",
+            " * @constructor",
+            " * @const",
+            " */ ",
+            "var module$exports$example=testcode$classdecl$var0"));
   }
 
   @Test
@@ -136,6 +143,7 @@ public void testSelfReference_qualifiedName() {
             "    alert(testcode$classdecl$var0);",
             "  }",
             "};",
+            "/** @constructor */",
             "outer.qual.Name = testcode$classdecl$var0;"));
   }
 
@@ -167,13 +175,13 @@ public void testVarAssignment() {
   }
 
   @Test
-  public void testJSDoc() {
+  public void testJSDocOnVar() {
     test(
         "/** @unrestricted */ var foo = class bar {};",
         lines(
             "/** @unrestricted */",
             "const testcode$classdecl$var0 = class {};",
-            "/** @unrestricted */",
+            "/** @unrestricted @constructor */",
             "var foo = testcode$classdecl$var0;"));
   }
 

test/com/google/javascript/jscomp/Es6RewriteClassTest.java

@@ -676,6 +676,7 @@ public void testNamedClassExpressionInVar() {
         lines(
             "/** @constructor @struct */",
             "const testcode$classdecl$var0 = function() {};",
+            "/** @constructor */",
             "var C = testcode$classdecl$var0;"));
   }
 
@@ -688,6 +689,7 @@ public void testNamedClassExpressionInVarWithMethod() {
             "const testcode$classdecl$var0 = function() {}",
             "testcode$classdecl$var0.prototype.foo = function() {};",
             "",
+            "/** @constructor */",
             "var C = testcode$classdecl$var0;"));
   }
 
@@ -1703,6 +1705,7 @@ public void testMultiNameClass_inVarDeclaration() {
         lines(
             "/** @constructor @struct */",
             "const testcode$classdecl$var0 = function(){};",
+            "/** @constructor */",
             "var F = testcode$classdecl$var0;"));
   }
 
@@ -1713,6 +1716,7 @@ public void testMultiNameClass_inAssignment() {
         lines(
             "/** @constructor @struct */",
             "const testcode$classdecl$var0 = function(){};",
+            "/** @constructor */",
             "F = testcode$classdecl$var0;"));
   }
 

test/com/google/javascript/jscomp/Es6TranspilationIntegrationTest.java

@@ -479,6 +479,7 @@ public void testClassExpressionInVar() {
         lines(
             "/** @constructor @struct @const */",
             "var testcode$classdecl$var0 = function() {};",
+            "/** @constructor */",
             "var C = testcode$classdecl$var0;"));
 
     test(
@@ -488,6 +489,7 @@ public void testClassExpressionInVar() {
             "var testcode$classdecl$var0 = function() {}",
             "testcode$classdecl$var0.prototype.foo = function() {};",
             "",
+            "/** @constructor */",
             "var C = testcode$classdecl$var0;"));
   }
 
@@ -1258,13 +1260,15 @@ public void testMultiNameClass() {
         lines(
             "/** @constructor @struct @const */",
             "var testcode$classdecl$var0 = function(){};",
+            "/** @constructor */",
             "var F = testcode$classdecl$var0;"));
 
     test(
         "F = class G {}",
         lines(
             "/** @constructor @struct @const */",
             "var testcode$classdecl$var0 = function(){};",
+            "/** @constructor */",
             "F = testcode$classdecl$var0;"));
   }