Follow ClassTypeAlias constructor redirections.

pkg/analyzer/lib/src/summary/index_unit.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
@@ skipping 355 matching lines @@
     if (fieldName != null) {
       Element element = fieldName.staticElement;
       recordRelation(element, IndexRelationKind.IS_REFERENCED_BY, fieldName);
     }
     node.expression?.accept(this);
   }
 
   @override
   visitConstructorName(ConstructorName node) {
     ConstructorElement element = node.staticElement;
-    // in 'class B = A;' actually A constructors are invoked
-    // TODO(scheglov) add support for multiple levels of redirection
-    // TODO(scheglov) test for a loop of redirection
-    if (element != null &&
-        element.isSynthetic &&
-        element.redirectedConstructor != null) {
-      element = element.redirectedConstructor;
-    }
+    element = _getActualConstructorElement(element);
     // record relation
     if (node.name != null) {
       int offset = node.period.offset;
       int length = node.name.end - offset;
       recordRelationOffset(
           element, IndexRelationKind.IS_REFERENCED_BY, offset, length);
     } else {
       int offset = node.type.end;
       recordRelationOffset(
           element, IndexRelationKind.IS_REFERENCED_BY, offset, 0);
@@ skipping 148 matching lines @@
       super.visitTypeName(node);
     }
   }
 
   @override
   visitWithClause(WithClause node) {
     for (TypeName typeName in node.mixinTypes) {
       recordSuperType(typeName, IndexRelationKind.IS_MIXED_IN_BY);
     }
   }
+
+  /**
+   * If the given [constructor] is a synthetic constructor created for a
+   * [ClassTypeAlias], return the actual constructor of a [ClassDeclaration]
+   * which is invoked.  Return `null` if a redirection cycle is detected.
+   */
+  ConstructorElement _getActualConstructorElement(
+      ConstructorElement constructor) {
+    Set<ConstructorElement> seenConstructors;
+    // follow zero or more redirections
+    while (constructor != null &&
+        constructor.isSynthetic &&
+        constructor.redirectedConstructor != null) {
+      constructor = constructor.redirectedConstructor;
+      // fail if a cycle is detected
+      if (seenConstructors?.add(constructor) == false) {
+        return null;
+      }
+      // done if no another redirection

[Paul Berry, 2016/02/29 21:28:01]

s/no another redirection/no more redirections/

+      if (constructor.redirectedConstructor == false) {

[Brian Wilkerson, 2016/02/29 21:27:18]

"false"?

Do we need this test anyway? Isn't it going to drop out of the while and then
return the constructor at the end of the method?

[Paul Berry, 2016/02/29 21:28:01]

I think you mean `== null`, not `== false`.

But I'm concerned that this bug wasn't found by unit tests.  Is it possible to
write a unit test that would have caught this bug?  If so, we should add that
test.  If not, perhaps this "if" test is not needed at all.

[scheglov, 2016/02/29 22:11:55]

Well, yes, it is going to drop out of the while on the next cycle.
But I as trying to avoid creating a new Set when we have just one redirection.
But maybe this is a premature optimization.
So, I'm removing this code and switch to always creating a new Set.

+        return constructor;
+      }
+      // delay the Set creation until we have a potential cycle
+      seenConstructors ??= new Set<ConstructorElement>();
+    }
+    return constructor;
+  }
 }
 
 /**
  * Information about a single relation.  Any [_RelationInfo] is always part
  * of a [_UnitIndexAssembler], so [offset] and [length] should be understood
  * within the context of the compilation unit pointed to by the
  * [_UnitIndexAssembler].
  */
 class _RelationInfo {
   final _ElementInfo elementInfo;
@@ skipping 52 matching lines @@
         usedElementKinds: relations.map((r) => r.kind).toList(),
         usedElementOffsets: relations.map((r) => r.offset).toList(),
         usedElementLengths: relations.map((r) => r.length).toList());
   }
 
   void defineName(String name, IndexNameKind kind, int offset) {
     int nameId = pkg._getStringId(name);
     definedNames.add(new _DefinedNameInfo(nameId, kind, offset));
   }
 }