Added no-tautology-expressions rule (#4470)

* add new rule implementation

* add some basic unit tests

* fix some issues in rule

* add noTautologyExpressionRule,
add unit tests

* add examples to rule description,
limit rule to validate only relational/logical expressions,
add tests

* fix typo in isRelationalOrLogicalOperator

* modify isLiteral to use tsutils
modified walk to cover additional cases
add property access unit tests

* modify error message

* add checks for ts.NullLiteral, ts.BooleanLiteral
add unit tests

src/configs/all.ts

@@ -133,6 +133,7 @@ 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": { options: ["allow-empty-class"] },
     "no-unsafe-any": true,

src/rules/noTautologyExpressionRule.ts

@@ -0,0 +1,101 @@
+/**
+ * @license
+ * Copyright 2019 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 =
+    "Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.";
+export class Rule extends Lint.Rules.AbstractRule {
+    public static metadata: Lint.IRuleMetadata = {
+        description: Lint.Utils.dedent`
+        Enforces that relational/equality binary operators does not take two equal variables/literals as operands.
+        Expression like 3 === 3, someVar === someVar, "1" > "1" are either a tautology or contradiction, and will produce an error.
+        `,
+        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) && isRelationalOrLogicalOperator(node.operatorToken)) {
+            if (
+                (tsutils.isStringLiteral(node.left) && tsutils.isStringLiteral(node.right)) ||
+                (tsutils.isNumericLiteral(node.left) && tsutils.isNumericLiteral(node.right))
+            ) {
+                if (node.left.text === node.right.text) {
+                    context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
+                }
+            } else if (tsutils.isIdentifier(node.left) && tsutils.isIdentifier(node.right)) {
+                if (node.left.text === node.right.text) {
+                    context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
+                }
+            } else if (
+                tsutils.isPropertyAccessExpression(node.left) &&
+                tsutils.isPropertyAccessExpression(node.right)
+            ) {
+                if (node.left.expression.getText() === node.right.expression.getText()) {
+                    if (node.left.name.text === node.right.name.text) {
+                        context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
+                    }
+                }
+            } else if (
+                (isBooleanLiteral(node.left) && isBooleanLiteral(node.right)) ||
+                (isNullLiteral(node.left) && isNullLiteral(node.right))
+            ) {
+                context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
+            }
+        }
+        return ts.forEachChild(node, cb);
+    };
+    return ts.forEachChild(context.sourceFile, cb);
+}
+
+function isNullLiteral(node: ts.Node): node is ts.NullLiteral {
+    return node.kind === ts.SyntaxKind.NullKeyword;
+}
+
+function isBooleanLiteral(node: ts.Node): node is ts.BooleanLiteral {
+    return node.kind === ts.SyntaxKind.TrueKeyword || node.kind === ts.SyntaxKind.FalseKeyword;
+}
+
+function isRelationalOrLogicalOperator(operator: ts.BinaryOperatorToken): boolean {
+    return new Set([
+        ts.SyntaxKind.LessThanToken,
+        ts.SyntaxKind.GreaterThanToken,
+        ts.SyntaxKind.LessThanEqualsToken,
+        ts.SyntaxKind.GreaterThanEqualsToken,
+        ts.SyntaxKind.EqualsEqualsToken,
+        ts.SyntaxKind.EqualsEqualsEqualsToken,
+        ts.SyntaxKind.ExclamationEqualsToken,
+        ts.SyntaxKind.ExclamationEqualsEqualsToken,
+        ts.SyntaxKind.AmpersandAmpersandToken,
+        ts.SyntaxKind.BarBarToken,
+    ]).has(operator.kind);
+}

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

@@ -0,0 +1,159 @@
+
+const expr = "someStr" === "someStr";
+             ~~~~~~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+const expr = 123 === 123;
+             ~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+const someVar = 100;
+const expr = someVar === someVar;
+             ~~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+
+const someFunc = () => {
+    if ("SomeStr" === "SomeStr") {
+        ~~~~~~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (100 === 100) {
+        ~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    let someVar = 100;
+    if (someVar === someVar) {
+        ~~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (1 !== 1) {
+        ~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (1 > 1) {
+        ~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const someVar = 123;
+    if (someVar < someVar) {
+        ~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if ("str" == "str") {
+        ~~~~~~~~~~~~~~ [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (123 != 123) {
+        ~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if ("str" <= "str") {
+        ~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if ("str" >= "str") {
+        ~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const someVar = true;
+    if (someVar || someVar) {
+        ~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const someVar = true;
+    if (someVar && someVar) {
+        ~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const someObj = { "name" : "moses the great" };
+    if (someObj.name === someObj.name) {
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const someObj = { "name" : "moses the great", "address" : "king's road 10" };
+    if (someObj.name === someObj.address) {
+        return true;
+    }
+}
+
+const someFunc = () => {
+    const objOne = { "name" : "moses the great" };
+    const objTwo = { "name" : "moses the great" };
+    if (objOne.name === objTwo.name) {
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (true === true) {
+        ~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (false === false) {
+        ~~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (true === false) {
+        ~~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (null === null) {
+        ~~~~~~~~~~~~~  [Both sides of this equality comparison are the same, so the expression is either a tautology or a contradiction.]
+        return true;
+    }
+}
+
+const someFunc = () => {
+    if (null === false) {
+        return true;
+    }
+}
+
+const someVar1 = 3 + 3;
+const someVar2 = 3 - 3;
+const someVar3 = 3 * 3;
+const someVar4 = 3 % 3;
+const someVar5 = 3 / 3;

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

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