Create a public API for contributing fixes and make fixes pluggable

pkg/analysis_server/lib/edit/fix/fix_core.dart

Index: pkg/analysis_server/lib/edit/fix/fix_core.dart
diff --git a/pkg/analysis_server/lib/edit/fix/fix_core.dart b/pkg/analysis_server/lib/edit/fix/fix_core.dart
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+// Copyright (c) 2015, 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.
+
+library analysis_server.edit.fix.fix_core;
+
+import 'package:analysis_server/src/protocol.dart' show SourceChange;
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/error.dart';
+
+/**
+ * A description of a single proposed fix for some problem.
+ */
+class Fix {
+  /**
+   * An empty list of fixes.
+   */
+  static const List<Fix> EMPTY_LIST = const <Fix>[];
+
+  /**
+   * A comparator that can be used to sort fixes by their relevance. The most
+   * relevant fixes will be sorted before fixes with a lower relevance.
+   */
+  static final Comparator<Fix> SORT_BY_RELEVANCE = (Fix firstFix,
+      Fix secondFix) => firstFix.kind.relevance - secondFix.kind.relevance;
+
+  /**
+   * A description of the fix being proposed.
+   */
+  final FixKind kind;
+
+  /**
+   * The change to be made in order to apply the fix.
+   */
+  final SourceChange change;
+
+  /**
+   * Initialize a newly created fix to have the given [kind] and [change].
+   */
+  Fix(this.kind, this.change);
+
+  @override
+  String toString() {
+    return 'Fix(kind=$kind, change=$change)';
+  }
+}
+
+/**
+ * An object used to produce fixes for a specific error. Fix contributors are
+ * long-lived objects and must not retain any state between invocations of
+ * [computeFixes].
+ */
+abstract class FixContributor {
+  /**
+   * Return a list of fixes for the given [error]. The error was reported
+   * after it's source was analyzed in the given [context].
+   */
+  List<Fix> computeFixes(AnalysisContext context, AnalysisError error);
+}
+
+/**
+ * A description of a class of fixes. Instances are intended to hold the
+ * information that is common across a number of fixes and to be shared by those
+ * fixes. For example, if an unnecessary cast is found then one of the suggested
+ * fixes will be to remove the cast. If there are multiple unnecessary casts in
+ * a single file, then there will be multiple fixes, one per occurance, but they
+ * will all share the same kind.
+ */
+class FixKind {
+  /**
+   * The name of this kind of fix, used for debugging.
+   */
+  final String name;
+
+  /**
+   * The relevance of this kind of fix for the kind of error being addressed.
+   */
+  final int relevance;
+
+  /**
+   * A human-readable description of the changes that will be applied by this
+   * kind of fix.
+   */
+  final String message;
+
+  /**
+   * Initialize a newly created kind of fix to have the given [name],
+   * [relevance] and [message].
+   */
+  const FixKind(this.name, this.relevance, this.message);
+
+  @override
+  String toString() => name;
+}