Mark RuleWalker and ProgramAwareRuleWalker as deprecated

src/language/walker/programAwareRuleWalker.ts

@@ -20,6 +20,7 @@ import * as ts from "typescript";
 import { IOptions } from "../rule/rule";
 import { RuleWalker } from "./ruleWalker";
 
+// tslint:disable-next-line:deprecation
 export class ProgramAwareRuleWalker extends RuleWalker {
     private readonly typeChecker: ts.TypeChecker;
 

src/language/walker/ruleWalker.ts

@@ -21,6 +21,12 @@ import { Fix, IOptions, Replacement, RuleFailure } from "../rule/rule";
 import { SyntaxWalker } from "./syntaxWalker";
 import { IWalker } from "./walker";
 
+/**
+ * @deprecated
+ * RuleWalker-based rules are slow,
+ * so it's generally preferable to use applyWithFunction instead of applyWithWalker.
+ * @see https://github.com/palantir/tslint/issues/2522
+ */
 export class RuleWalker extends SyntaxWalker implements IWalker {
     private readonly limit: number;
     private readonly options?: any[];