Add strict-comparisons Rule (#4519)

* add noAsyncWithoutAwait rule

* fix lint

* code review updates

* allow return as well as await

* remove unneeded lint ignore

* improve rationale & fix performance issue

* fixes according to review

* finish fixing according to review

* Add `no-object-comparison` rule

* Revert styling

* Fix code styling

* Fix enum error

* Rename object-comparison rule

* Rename test folder of object-comparison rule

* Change rule argument to object

* Refactor object-comparison rule

* Add new option to object-comparison rule

* Add more test cases

* Handle numeric and string enums

* Fix corner cases with undefined

* Make rule compatible with ts 2.1

* feat(strict-comparisons): rename rule, fix error message, add example

* feat(strict-comparisons): update examples url

* Initial feedback cleanups

* Refactored to walk function

* Disabled strict-comparisons in tslint.json

* Delete unused objectComparisonRule.ts

* Un-formatted src/configs/all.ts

* Un-formatted tslint.json

* Excluded string enum complaints from TS 2.1

* Formatted strictComparisonsRule.ts

* Some more TS 2.1 disabling

* I'm here all night folks

Author: AndreasGassmann

src/configs/all.ts

@@ -150,6 +150,7 @@ export const rules = {
     "restrict-plus-operands": true,
     "static-this": true,
     "strict-boolean-expressions": true,
+    "strict-comparisons": true,
     "strict-type-predicates": true,
     "switch-default": true,
     "triple-equals": true,

src/rules/code-examples/strictComparisons.examples.ts

@@ -0,0 +1,71 @@
+/**
+ * @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 Lint from "../../index";
+
+// tslint:disable: object-literal-sort-keys
+export const codeExamples = [
+    {
+        description: "Disallows usage of comparison operators with non-primitive types.",
+        config: Lint.Utils.dedent`
+            "rules": { "strict-comparisons": true }
+        `,
+        pass: Lint.Utils.dedent`
+            const object1 = {};
+            const object2 = {};
+            if (isEqual(object1, object2)) {}
+        `,
+        fail: Lint.Utils.dedent`
+            const object1 = {};
+            const object2 = {};
+            if (object1 === object2) {}
+        `,
+    },
+    {
+        description:
+            "Allows equality operators to be used with non-primitive types, while still disallowing the use of greater than and less than.",
+        config: Lint.Utils.dedent`
+            "rules": { "strict-comparisons": [true, {  "allow-object-equal-comparison": true }] }
+        `,
+        pass: Lint.Utils.dedent`
+            const object1 = {};
+            const object2 = {};
+            if (object1 === object2) {}
+        `,
+        fail: Lint.Utils.dedent`
+            const object1 = {};
+            const object2 = {};
+            if (object1 < object2) {}
+        `,
+    },
+    {
+        description: "Allows ordering operators to be used with string types.",
+        config: Lint.Utils.dedent`
+            "rules": { "strict-comparisons": [true, {  "allow-string-order-comparison": true }] }
+        `,
+        pass: Lint.Utils.dedent`
+            const string1 = "";
+            const string2 = "";
+            if (string1 < string2) {}
+        `,
+        fail: Lint.Utils.dedent`
+            const object1 = {};
+            const object2 = {};
+            if (object1 < object2) {}
+        `,
+    },
+];

src/rules/strictComparisonsRule.ts

@@ -0,0 +1,288 @@
+/**
+ * @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 { isBinaryExpression, isTypeFlagSet, isUnionType } from "tsutils";
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+
+import { codeExamples } from "./code-examples/strictComparisons.examples";
+
+const OPTION_ALLOW_OBJECT_EQUAL_COMPARISON = "allow-object-equal-comparison";
+const OPTION_ALLOW_STRING_ORDER_COMPARISON = "allow-string-order-comparison";
+
+const enum TypeKind {
+    Any = 0,
+    Number = 1,
+    Enum = 2,
+    String = 3,
+    Boolean = 4,
+    Null = 5,
+    Undefined = 6,
+    Object = 7,
+}
+
+const typeNames = {
+    [TypeKind.Any]: "any",
+    [TypeKind.Number]: "number",
+    [TypeKind.Enum]: "enum",
+    [TypeKind.String]: "string",
+    [TypeKind.Boolean]: "boolean",
+    [TypeKind.Null]: "null",
+    [TypeKind.Undefined]: "undefined",
+    [TypeKind.Object]: "object",
+};
+
+interface Options {
+    [OPTION_ALLOW_OBJECT_EQUAL_COMPARISON]?: boolean;
+    [OPTION_ALLOW_STRING_ORDER_COMPARISON]?: boolean;
+}
+
+export class Rule extends Lint.Rules.TypedRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "strict-comparisons",
+        description: "Only allow comparisons between primitives.",
+        optionsDescription: Lint.Utils.dedent`
+                One of the following arguments may be optionally provided:
+                * \`${OPTION_ALLOW_OBJECT_EQUAL_COMPARISON}\` allows \`!=\` \`==\` \`!==\` \`===\` comparison between any types.
+                * \`${OPTION_ALLOW_STRING_ORDER_COMPARISON}\` allows \`>\` \`<\` \`>=\` \`<=\` comparison between strings.`,
+        options: {
+            type: "object",
+            properties: {
+                [OPTION_ALLOW_OBJECT_EQUAL_COMPARISON]: {
+                    type: "boolean",
+                },
+                [OPTION_ALLOW_STRING_ORDER_COMPARISON]: {
+                    type: "boolean",
+                },
+            },
+        },
+        optionExamples: [
+            true,
+            [
+                true,
+                {
+                    [OPTION_ALLOW_OBJECT_EQUAL_COMPARISON]: false,
+                    [OPTION_ALLOW_STRING_ORDER_COMPARISON]: false,
+                },
+            ],
+        ],
+        rationale: Lint.Utils.dedent`
+                When using comparison operators to compare objects, they compare references and not values.
+                This is often done accidentally.
+                With this rule, \`>\`, \`>=\`, \`<\`, \`<=\` operators are only allowed when comparing \`numbers\`.
+                \`===\`, \`!==\` are allowed for \`number\` \`string\` and \`boolean\` types and if one of the
+                operands is \`null\` or \`undefined\`.
+            `,
+        type: "functionality",
+        typescriptOnly: false,
+        requiresTypeInfo: true,
+        codeExamples,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static INVALID_TYPES(types1: TypeKind[], types2: TypeKind[]) {
+        const types1String = types1.map(type => typeNames[type]).join(" | ");
+        const types2String = types2.map(type => typeNames[type]).join(" | ");
+
+        return `Cannot compare type '${types1String}' to type '${types2String}'.`;
+    }
+
+    public static INVALID_TYPE_FOR_OPERATOR(type: TypeKind, comparator: string) {
+        return `Cannot use '${comparator}' comparator for type '${typeNames[type]}'.`;
+    }
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk, this.getRuleOptions(), program);
+    }
+
+    private getRuleOptions(): Options {
+        if (this.ruleArguments[0] === undefined) {
+            return {};
+        } else {
+            return this.ruleArguments[0] as Options;
+        }
+    }
+}
+
+function walk(ctx: Lint.WalkContext<Options>, program: ts.Program) {
+    const { sourceFile, options } = ctx;
+
+    const checker = program.getTypeChecker();
+
+    return ts.forEachChild(sourceFile, function cb(node: ts.Node): void {
+        if (isBinaryExpression(node) && isComparisonOperator(node)) {
+            const leftType = checker.getTypeAtLocation(node.left);
+            const rightType = checker.getTypeAtLocation(node.right);
+
+            const leftKinds: TypeKind[] = getTypes(leftType);
+            const rightKinds: TypeKind[] = getTypes(rightType);
+
+            const operandKind = getStrictestComparableType(leftKinds, rightKinds);
+
+            if (operandKind === undefined) {
+                const failureString = Rule.INVALID_TYPES(leftKinds, rightKinds);
+                ctx.addFailureAtNode(node, failureString);
+            } else {
+                const failureString = Rule.INVALID_TYPE_FOR_OPERATOR(
+                    operandKind,
+                    node.operatorToken.getText(),
+                );
+                const isEquality = isEqualityOperator(node);
+                if (isEquality) {
+                    // Check !=, ==, !==, ===
+                    switch (operandKind) {
+                        case TypeKind.Any:
+                        case TypeKind.Number:
+                        case TypeKind.Enum:
+                        case TypeKind.String:
+                        case TypeKind.Boolean:
+                            break;
+                        case TypeKind.Null:
+                        case TypeKind.Undefined:
+                        case TypeKind.Object:
+                            if (options[OPTION_ALLOW_OBJECT_EQUAL_COMPARISON]) {
+                                break;
+                            }
+                            ctx.addFailureAtNode(node, failureString);
+                            break;
+                        default:
+                            ctx.addFailureAtNode(node, failureString);
+                    }
+                } else {
+                    // Check >, <, >=, <=
+                    switch (operandKind) {
+                        case TypeKind.Any:
+                        case TypeKind.Number:
+                            break;
+                        case TypeKind.String:
+                            if (options[OPTION_ALLOW_STRING_ORDER_COMPARISON]) {
+                                break;
+                            }
+                            ctx.addFailureAtNode(node, failureString);
+                            break;
+                        default:
+                            ctx.addFailureAtNode(node, failureString);
+                    }
+                }
+            }
+        }
+        return ts.forEachChild(node, cb);
+    });
+}
+
+function getTypes(types: ts.Type): TypeKind[] {
+    // Compatibility for TypeScript pre-2.4, which used EnumLiteralType instead of LiteralType
+    const baseType = ((types as any) as { baseType: ts.LiteralType }).baseType;
+    return isUnionType(types)
+        ? Array.from(new Set(types.types.map(getKind)))
+        : isTypeFlagSet(types, ts.TypeFlags.EnumLiteral) && typeof baseType !== "undefined"
+        ? [getKind(baseType)]
+        : [getKind(types)];
+}
+
+function getStrictestComparableType(
+    typesLeft: TypeKind[],
+    typesRight: TypeKind[],
+): TypeKind | undefined {
+    const overlappingTypes = typesLeft.filter(type => typesRight.indexOf(type) >= 0);
+
+    if (overlappingTypes.length > 0) {
+        return getStrictestKind(overlappingTypes);
+    } else {
+        // In case one of the types is "any", get the strictest type of the other array
+        if (arrayContainsKind(typesLeft, [TypeKind.Any])) {
+            return getStrictestKind(typesRight);
+        }
+        if (arrayContainsKind(typesRight, [TypeKind.Any])) {
+            return getStrictestKind(typesLeft);
+        }
+
+        // In case one array contains NullOrUndefined and the other an Object, return Object
+        if (
+            (arrayContainsKind(typesLeft, [TypeKind.Null, TypeKind.Undefined]) &&
+                arrayContainsKind(typesRight, [TypeKind.Object])) ||
+            (arrayContainsKind(typesRight, [TypeKind.Null, TypeKind.Undefined]) &&
+                arrayContainsKind(typesLeft, [TypeKind.Object]))
+        ) {
+            return TypeKind.Object;
+        }
+        return undefined;
+    }
+}
+
+function arrayContainsKind(types: TypeKind[], typeToCheck: TypeKind[]): boolean {
+    return types.some(type => typeToCheck.indexOf(type) >= 0);
+}
+
+function getStrictestKind(types: TypeKind[]): TypeKind {
+    // tslint:disable-next-line:no-unsafe-any
+    return Math.max.apply(Math, types);
+}
+
+function isComparisonOperator(node: ts.BinaryExpression): boolean {
+    switch (node.operatorToken.kind) {
+        case ts.SyntaxKind.LessThanToken:
+        case ts.SyntaxKind.GreaterThanToken:
+        case ts.SyntaxKind.LessThanEqualsToken:
+        case ts.SyntaxKind.GreaterThanEqualsToken:
+        case ts.SyntaxKind.EqualsEqualsToken:
+        case ts.SyntaxKind.ExclamationEqualsToken:
+        case ts.SyntaxKind.EqualsEqualsEqualsToken:
+        case ts.SyntaxKind.ExclamationEqualsEqualsToken:
+            return true;
+        default:
+            return false;
+    }
+}
+
+function isEqualityOperator(node: ts.BinaryExpression): boolean {
+    switch (node.operatorToken.kind) {
+        case ts.SyntaxKind.EqualsEqualsToken:
+        case ts.SyntaxKind.ExclamationEqualsToken:
+        case ts.SyntaxKind.EqualsEqualsEqualsToken:
+        case ts.SyntaxKind.ExclamationEqualsEqualsToken:
+            return true;
+        default:
+            return false;
+    }
+}
+
+function getKind(type: ts.Type): TypeKind {
+    // tslint:disable:no-bitwise
+    if (is(ts.TypeFlags.String | ts.TypeFlags.StringLiteral)) {
+        return TypeKind.String;
+    } else if (is(ts.TypeFlags.Number | ts.TypeFlags.NumberLiteral)) {
+        return TypeKind.Number;
+    } else if (is(ts.TypeFlags.BooleanLike)) {
+        return TypeKind.Boolean;
+    } else if (is(ts.TypeFlags.Null)) {
+        return TypeKind.Null;
+    } else if (is(ts.TypeFlags.Undefined)) {
+        return TypeKind.Undefined;
+    } else if (is(ts.TypeFlags.Any)) {
+        return TypeKind.Any;
+    } else {
+        return TypeKind.Object;
+    }
+    // tslint:enable:no-bitwise
+
+    function is(flags: ts.TypeFlags) {
+        return isTypeFlagSet(type, flags);
+    }
+}