Merge pull request #5875 from weswigham/no-in-rule

lint rule forbidding the in keyword binary expression

Jakefile.js

@@ -113,7 +113,8 @@ var scriptSources = [
     "tslint/nextLineRule.ts",
     "tslint/noNullRule.ts",
     "tslint/preferConstRule.ts",
-    "tslint/typeOperatorSpacingRule.ts"
+    "tslint/typeOperatorSpacingRule.ts",
+    "tslint/noInOperatorRule.ts"
 ].map(function (f) {
     return path.join(scriptsDirectory, f);
 });
@@ -875,7 +876,8 @@ var tslintRules = ([
     "noNullRule",
     "preferConstRule",
     "booleanTriviaRule",
-    "typeOperatorSpacingRule"
+    "typeOperatorSpacingRule",
+    "noInOperatorRule"
 ]);
 var tslintRulesFiles = tslintRules.map(function(p) {
     return path.join(tslintRuleDir, p + ".ts");

scripts/tslint/noInOperatorRule.ts

@@ -0,0 +1,20 @@
+import * as Lint from "tslint/lib/lint";
+import * as ts from "typescript";
+
+
+export class Rule extends Lint.Rules.AbstractRule {
+    public static FAILURE_STRING = "Don't use the 'in' keyword - use 'hasProperty' to check for key presence instead";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithWalker(new InWalker(sourceFile, this.getOptions()));
+    }
+}
+
+class InWalker extends Lint.RuleWalker {
+    visitNode(node: ts.Node) {
+        super.visitNode(node);
+        if (node.kind === ts.SyntaxKind.InKeyword && node.parent && node.parent.kind === ts.SyntaxKind.BinaryExpression) {
+            this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+        }
+    }
+}

tslint.json

@@ -40,6 +40,7 @@
         "no-null": true,
         "boolean-trivia": true,
         "type-operator-spacing": true,
-        "prefer-const": true
+        "prefer-const": true,
+        "no-in-operator": true
   }
 }