Revert "Add error for mixins defining conflicting private names (issue 28809)"

pkg/analyzer/lib/src/generated/error_verifier.dart

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index cdf4a8f3e40e818b949bbc3cccb388655f3558ab..adc6f11aaf184b71a80c82c019de5033fc8447a3 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -486,7 +486,6 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
           _checkImplementsSuperClass(node);
           _checkImplementsFunctionWithoutCall(node);
           _checkForMixinHasNoConstructors(node);
-          _checkForMixinWithConflictingPrivateMember(node);
         }
       }
       visitClassDeclarationIncrementally(node);
@@ -4891,80 +4890,6 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
   }
 
   /**
-   * Check for the declaration of a mixin from a library other than the current
-   * library that defines a private member that conflicts with a private name
-   * from the same library but from a superclass or a different mixin.
-   */
-  void _checkForMixinWithConflictingPrivateMember(ClassDeclaration node) {
-    WithClause withClause = node.withClause;
-    if (withClause == null) {
-      return;
-    }
-    DartType declaredSupertype = node.extendsClause?.superclass?.type;
-    if (declaredSupertype is! InterfaceType) {
-      return;
-    }
-    InterfaceType superclass = declaredSupertype;
-    Map<LibraryElement, Map<String, String>> mixedInNames =
-        <LibraryElement, Map<String, String>>{};
-
-    /**
-     * Report an error and return `true` if the given [name] is a private name
-     * (which is defined in the given [library]) and it conflicts with another
-     * definition of that name inherited from the superclass.
-     */
-    bool isConflictingName(
-        String name, LibraryElement library, TypeName typeName) {
-      if (Identifier.isPrivateName(name)) {
-        Map<String, String> names =
-            mixedInNames.putIfAbsent(library, () => <String, String>{});
-        if (names.containsKey(name)) {
-          _errorReporter.reportErrorForNode(
-              CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-              typeName,
-              [name, typeName.name.name, names[name]]);
-          return true;
-        }
-        names[name] = typeName.name.name;
-        ExecutableElement inheritedMember =
-            superclass.lookUpMethod(name, library) ??
-                superclass.lookUpGetter(name, library) ??
-                superclass.lookUpSetter(name, library);
-        if (inheritedMember != null) {
-          _errorReporter.reportErrorForNode(
-              CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-              typeName, [
-            name,
-            typeName.name.name,
-            inheritedMember.enclosingElement.name
-          ]);
-          return true;
-        }
-      }
-      return false;
-    }
-
-    for (TypeName mixinType in withClause.mixinTypes) {
-      DartType type = mixinType.type;
-      if (type is InterfaceType) {
-        LibraryElement library = type.element.library;
-        if (library != _currentLibrary) {
-          for (PropertyAccessorElement accessor in type.accessors) {
-            if (isConflictingName(accessor.name, library, mixinType)) {
-              return;
-            }
-          }
-          for (MethodElement method in type.methods) {
-            if (isConflictingName(method.name, library, mixinType)) {
-              return;
-            }
-          }
-        }
-      }
-    }
-  }
-
-  /**
    * Verify that the given [constructor] has at most one 'super' initializer.
    *
    * See [CompileTimeErrorCode.MULTIPLE_SUPER_INITIALIZERS].