Issue #1054 - Ported the use-isnan rule from tslint-microsoft-contrib…

README.md

@@ -292,6 +292,7 @@ A sample configuration file with all options is available [here](https://github.
     * `"parameter"` checks function parameters.
     * `"property-declaration"` checks object property declarations.
     * `"variable-declaration"` checks variable declaration.
+* `use-isnan` enforces that you use the isNaN() function to check for NaN references instead of a comparison to the NaN constant. Similar to the [use-isnan ESLint rule](http://eslint.org/docs/rules/use-isnan).
 * `use-strict` enforces ECMAScript 5's strict mode.
     * `check-module` checks that all top-level modules are using strict mode.
     * `check-function` checks that all top-level functions are using strict mode.

src/rules/useIsnanRule.ts

@@ -0,0 +1,44 @@
+/**
+ * @license
+ * Copyright 2013 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+import * as Lint from "../lint";
+
+/**
+ * Implementation of the use-isnan rule.
+ */
+export class Rule extends Lint.Rules.AbstractRule {
+    public static FAILURE_STRING = "Found an invalid comparison for NaN: ";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithWalker(new UseIsnanRuleWalker(sourceFile, this.getOptions()));
+    }
+}
+
+class UseIsnanRuleWalker extends Lint.RuleWalker {
+
+    protected visitBinaryExpression(node: ts.BinaryExpression): void {
+        if (this.isExpressionNaN(node.left) || this.isExpressionNaN(node.right)) {
+            this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING + node.getText()));
+        }
+        super.visitBinaryExpression(node);
+    }
+
+    private isExpressionNaN(node: ts.Node) {
+        return node.kind === ts.SyntaxKind.Identifier && node.getText() === "NaN";
+    }
+}

src/tsconfig.json

@@ -114,6 +114,7 @@
         "rules/tripleEqualsRule.ts",
         "rules/typedefRule.ts",
         "rules/typedefWhitespaceRule.ts",
+        "rules/useIsnanRule.ts",
         "rules/useStrictRule.ts",
         "rules/variableNameRule.ts",
         "rules/whitespaceRule.ts",

test/rules/use-isnan/test.ts.lint

@@ -0,0 +1,28 @@
+
+// no violation for comparing NaN using isNaN
+if (isNaN(NaN)) {
+}
+
+// no violation for correctly checking for isNaN
+if (isNaN(something)) { }
+
+
+// do not use equality operators to compare for NaN
+if (foo == NaN) {  }
+    ~~~~~~~~~~         [Found an invalid comparison for NaN: foo == NaN]
+if (NaN === foo) {  }
+    ~~~~~~~~~~~        [Found an invalid comparison for NaN: NaN === foo]
+if (foo != NaN) {  }
+    ~~~~~~~~~~         [Found an invalid comparison for NaN: foo != NaN]
+if (NaN !== foo) {  }
+    ~~~~~~~~~~~        [Found an invalid comparison for NaN: NaN !== foo]
+
+// do not use any binary operators to compare for NaN
+if (foo > NaN) { }
+    ~~~~~~~~~         [Found an invalid comparison for NaN: foo > NaN]
+if (NaN >= foo) { }
+    ~~~~~~~~~~        [Found an invalid comparison for NaN: NaN >= foo]
+if (foo < NaN) { }
+    ~~~~~~~~~         [Found an invalid comparison for NaN: foo < NaN]
+if (NaN <= foo) { }
+    ~~~~~~~~~~        [Found an invalid comparison for NaN: NaN <= foo]

test/rules/use-isnan/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "use-isnan": true
+  }
+}

test/tsconfig.json

@@ -111,6 +111,7 @@
         "../src/rules/tripleEqualsRule.ts",
         "../src/rules/typedefRule.ts",
         "../src/rules/typedefWhitespaceRule.ts",
+        "../src/rules/useIsnanRule.ts",
         "../src/rules/useStrictRule.ts",
         "../src/rules/variableNameRule.ts",
         "../src/rules/whitespaceRule.ts",
@@ -142,4 +143,4 @@
         "rule-tester/testData.ts",
         "rule-tester/utilsTests.ts"
     ]
-}
+}