Added no-tautology-expression rule

src/configs/all.ts

@@ -129,6 +129,7 @@ export const rules = {
     "no-string-throw": true,
     "no-sparse-arrays": true,
     "no-submodule-imports": true,
+    "no-tautology-expression": true,
     "no-unbound-method": true,
     "no-unnecessary-class": [true, "allow-empty-class"],
     "no-unsafe-any": true,

src/rules/noTautologyExpressionRule.ts

@@ -0,0 +1,58 @@
+/**
+ * @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 tsutils from "tsutils";
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+
+const TAUTOLOGY_DISCOVERED_ERROR_STRING = "Expression is a tautology. Comparison is redundant.";
+export class Rule extends Lint.Rules.AbstractRule {
+    public static metadata: Lint.IRuleMetadata = {
+        description: "Enforces that two equal variables or literals are not compared.",
+        optionExamples: [true],
+        options: null,
+        optionsDescription: "Not configurable.",
+        rationale: `Clean redundant code and unnecessary comparison of objects and literals.`,
+        ruleName: "no-tautology-expression",
+        type: "functionality",
+        typescriptOnly: false,
+    };
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk);
+    }
+}
+
+function walk(context: Lint.WalkContext<void>) {
+    const cb = (node: ts.Node): void => {
+        if (tsutils.isBinaryExpression(node)) {
+            if (isLiteral(node.left) && isLiteral(node.right)) {
+                // Simple textual comparison of both sides
+                if (node.left.getText() === node.right.getText()) {
+                    context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
+                }
+            }
+        }
+        return ts.forEachChild(node, cb);
+    };
+    return ts.forEachChild(context.sourceFile, cb);
+}
+
+function isLiteral(node: ts.Node): boolean {
+    return tsutils.isStringLiteral(node) || tsutils.isNumericLiteral(node);
+}

test/rules/no-tautology-expression/test.ts.lint

@@ -0,0 +1,30 @@
+const expr = "someStr" === "someStr";
+             ~~~~~~~~~~~~~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+const expr = 123 === 123;
+             ~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+const someVar = 100;
+const expr = someVar === someVar;
+             ~~~~~~~~~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+
+const someFunc = () => {
+    if ("SomeStr" === "SomeStr") {
+        ~~~~~~~~~~~~~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (100 === 100) {
+        ~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    let someVar = 100;
+    if (someVar === someVar) {
+        ~~~~~~~~~~~~~~~~~~~  [Expression is a tautology. Comparison is redundant.]
+        return true;
+    }
+}
+

test/rules/no-tautology-expression/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-tautology-expression": true
+  }
+}