no-unnecessary-condition.test.ts

import {
  TestCaseError,
  InvalidTestCase,
} from '@typescript-eslint/experimental-utils/dist/ts-eslint';
import rule, {
  Options,
  MessageId,
} from '../../src/rules/no-unnecessary-condition';
import { RuleTester, getFixturesRootDir, noFormat } from '../RuleTester';

const rootPath = getFixturesRootDir();

const ruleTester = new RuleTester({
  parser: '@typescript-eslint/parser',
  parserOptions: {
    tsconfigRootDir: rootPath,
    project: './tsconfig.json',
  },
});

const ruleError = (
  line: number,
  column: number,
  messageId: MessageId,
): TestCaseError<MessageId> => ({
  messageId,
  line,
  column,
});

const necessaryConditionTest = (condition: string): string => `
declare const b1: ${condition};
declare const b2: boolean;
const t1 = b1 && b2;
`;

const unnecessaryConditionTest = (
  condition: string,
  messageId: MessageId,
): InvalidTestCase<MessageId, Options> => ({
  code: necessaryConditionTest(condition),
  errors: [ruleError(4, 12, messageId)],
});

ruleTester.run('no-unnecessary-conditionals', rule, {
  valid: [
    `
declare const b1: boolean;
declare const b2: boolean;
const t1 = b1 && b2;
const t2 = b1 || b2;
if (b1 && b2) {
}
while (b1 && b2) {}
for (let i = 0; b1 && b2; i++) {
  break;
}
const t1 = b1 && b2 ? 'yes' : 'no';
if (b1 && b2) {
}
while (b1 && b2) {}
for (let i = 0; b1 && b2; i++) {
  break;
}
const t1 = b1 && b2 ? 'yes' : 'no';
for (;;) {}
    `,
    necessaryConditionTest('false | 5'), // Truthy literal and falsy literal
    necessaryConditionTest('boolean | "foo"'), // boolean and truthy literal
    necessaryConditionTest('0 | boolean'), // boolean and falsy literal
    necessaryConditionTest('boolean | object'), // boolean and always-truthy type
    necessaryConditionTest('false | object'), // always truthy type and falsy literal
    // always falsy type and always truthy type
    necessaryConditionTest('null | object'),
    necessaryConditionTest('undefined | true'),
    necessaryConditionTest('void | true'),

    necessaryConditionTest('any'), // any
    necessaryConditionTest('unknown'), // unknown

    // Generic type params
    `
function test<T extends string>(t: T) {
  return t ? 'yes' : 'no';
}
    `,
    `
// Naked type param
function test<T>(t: T) {
  return t ? 'yes' : 'no';
}
    `,
    `
// Naked type param in union
function test<T>(t: T | []) {
  return t ? 'yes' : 'no';
}
    `,

    // Boolean expressions
    `
function test(a: string) {
  return a === 'a';
}
    `,
    `
function test(a?: string) {
  const t1 = a === undefined;
  const t3 = undefined === a;
}
    `,

    /**
     * Predicate functions
     **/
    // valid, with the flag off
    `
[1, 3, 5].filter(() => true);
[1, 2, 3].find(() => false);
function truthy() {
  return [];
}
function falsy() {}
[1, 3, 5].filter(truthy);
[1, 2, 3].find(falsy);
    `,
    {
      options: [{ checkArrayPredicates: true }],
      code: `
// with literal arrow function
[0, 1, 2].filter(x => x);

// filter with named function
function length(x: string) {
  return x.length;
}
['a', 'b', ''].filter(length);

// with non-literal array
function nonEmptyStrings(x: string[]) {
  return x.filter(length);
}
      `,
    },
    // Ignores non-array methods of the same name
    {
      options: [{ checkArrayPredicates: true }],
      code: `
const notArray = {
  filter: (func: () => boolean) => func(),
  find: (func: () => boolean) => func(),
};
notArray.filter(() => true);
notArray.find(() => true);
      `,
    },

    // Nullish coalescing operator
    `
function test(a: string | null) {
  return a ?? 'default';
}
    `,
    `
function test(a: string | undefined) {
  return a ?? 'default';
}
    `,
    `
function test(a: string | null | undefined) {
  return a ?? 'default';
}
    `,
    `
function test(a: unknown) {
  return a ?? 'default';
}
    `,
    // Indexing cases
    `
declare const arr: object[];
if (arr[42]) {
} // looks unnecessary from the types, but isn't

const tuple = [{}] as [object];
declare const n: number;
if (tuple[n]) {
}
    `,
    // Optional-chaining indexing
    `
declare const arr: Array<{ value: string } & (() => void)>;
if (arr[42]?.value) {
}
arr[41]?.();

// An array access can "infect" deeper into the chain
declare const arr2: Array<{ x: { y: { z: object } } }>;
arr2[42]?.x?.y?.z;

const tuple = ['foo'] as const;
declare const n: number;
tuple[n]?.toUpperCase();
    `,
    `
if (arr?.[42]) {
}
    `,
    `
declare const returnsArr: undefined | (() => string[]);
if (returnsArr?.()[42]) {
}
returnsArr?.()[42]?.toUpperCase();
    `,
    // nullish + array index
    `
declare const arr: string[][];
arr[x] ?? [];
    `,
    // Doesn't check the right-hand side of a logical expression
    //  in a non-conditional context
    {
      code: `
declare const b1: boolean;
declare const b2: true;
const x = b1 && b2;
      `,
    },
    {
      code: `
while (true) {}
for (; true; ) {}
do {} while (true);
      `,
      options: [{ allowConstantLoopConditions: true }],
    },
    `
let foo: undefined | { bar: true };
foo?.bar;
    `,
    `
let foo: null | { bar: true };
foo?.bar;
    `,
    `
let foo: undefined;
foo?.bar;
    `,
    `
let foo: undefined;
foo?.bar.baz;
    `,
    `
let foo: null;
foo?.bar;
    `,
    `
let anyValue: any;
anyValue?.foo;
    `,
    `
let unknownValue: unknown;
unknownValue?.foo;
    `,
    `
let foo: undefined | (() => {});
foo?.();
    `,
    `
let foo: null | (() => {});
foo?.();
    `,
    `
let foo: undefined;
foo?.();
    `,
    `
let foo: undefined;
foo?.().bar;
    `,
    `
let foo: null;
foo?.();
    `,
    `
let anyValue: any;
anyValue?.();
    `,
    `
let unknownValue: unknown;
unknownValue?.();
    `,
    'const foo = [1, 2, 3][0];',
  ],
  invalid: [
    // Ensure that it's checking in all the right places
    {
      code: `
const b1 = true;
declare const b2: boolean;
const t1 = b1 && b2;
const t2 = b1 || b2;
if (b1 && b2) {
}
if (b2 && b1) {
}
while (b1 && b2) {}
while (b2 && b1) {}
for (let i = 0; b1 && b2; i++) {
  break;
}
const t1 = b1 && b2 ? 'yes' : 'no';
const t1 = b2 && b1 ? 'yes' : 'no';
      `,
      errors: [
        ruleError(4, 12, 'alwaysTruthy'),
        ruleError(5, 12, 'alwaysTruthy'),
        ruleError(6, 5, 'alwaysTruthy'),
        ruleError(8, 11, 'alwaysTruthy'),
        ruleError(10, 8, 'alwaysTruthy'),
        ruleError(11, 14, 'alwaysTruthy'),
        ruleError(12, 17, 'alwaysTruthy'),
        ruleError(15, 12, 'alwaysTruthy'),
        ruleError(16, 18, 'alwaysTruthy'),
      ],
    },
    // Ensure that it's complaining about the right things
    unnecessaryConditionTest('object', 'alwaysTruthy'),
    unnecessaryConditionTest('object | true', 'alwaysTruthy'),
    unnecessaryConditionTest('"" | false', 'alwaysFalsy'), // Two falsy literals
    unnecessaryConditionTest('"always truthy"', 'alwaysTruthy'),
    unnecessaryConditionTest(`undefined`, 'alwaysFalsy'),
    unnecessaryConditionTest('null', 'alwaysFalsy'),
    unnecessaryConditionTest('void', 'alwaysFalsy'),
    unnecessaryConditionTest('never', 'never'),

    // More complex logical expressions
    {
      code: `
declare const b1: boolean;
declare const b2: boolean;
if (true && b1 && b2) {
}
if (b1 && false && b2) {
}
if (b1 || b2 || true) {
}
      `,
      errors: [
        ruleError(4, 5, 'alwaysTruthy'),
        ruleError(6, 11, 'alwaysFalsy'),
        ruleError(8, 17, 'alwaysTruthy'),
      ],
    },

    // Generic type params
    {
      code: `
function test<T extends object>(t: T) {
  return t ? 'yes' : 'no';
}
      `,
      errors: [ruleError(3, 10, 'alwaysTruthy')],
    },
    {
      code: `
function test<T extends false>(t: T) {
  return t ? 'yes' : 'no';
}
      `,
      errors: [ruleError(3, 10, 'alwaysFalsy')],
    },
    {
      code: `
function test<T extends 'a' | 'b'>(t: T) {
  return t ? 'yes' : 'no';
}
      `,
      errors: [ruleError(3, 10, 'alwaysTruthy')],
    },

    // Boolean expressions
    {
      code: `
function test(a: 'a') {
  return a === 'a';
}
      `,
      errors: [ruleError(3, 10, 'literalBooleanExpression')],
    },
    {
      code: `
const y = 1;
if (y === 0) {
}
      `,
      errors: [ruleError(3, 5, 'literalBooleanExpression')],
    },
    {
      code: `
enum Foo {
  a = 1,
  b = 2,
}

const x = Foo.a;
if (x === Foo.a) {
}
      `,
      errors: [ruleError(8, 5, 'literalBooleanExpression')],
    },
    // Workaround https://github.com/microsoft/TypeScript/issues/37160
    {
      code: `
function test(a: string) {
  const t1 = a !== undefined;
  const t3 = undefined === a;
}
      `,
      errors: [
        ruleError(3, 14, 'noOverlapBooleanExpression'),
        ruleError(4, 14, 'noOverlapBooleanExpression'),
      ],
    },
    {
      code: `
function test(a?: string) {
  const t1 = a === null;
  const t3 = null !== a;
}
      `,
      errors: [
        ruleError(3, 14, 'noOverlapBooleanExpression'),
        ruleError(4, 14, 'noOverlapBooleanExpression'),
      ],
    },
    // Nullish coalescing operator
    {
      code: `
function test(a: string) {
  return a ?? 'default';
}
      `,
      errors: [ruleError(3, 10, 'neverNullish')],
    },
    {
      code: `
function test(a: string | false) {
  return a ?? 'default';
}
      `,
      errors: [ruleError(3, 10, 'neverNullish')],
    },
    {
      code: `
function test(a: null) {
  return a ?? 'default';
}
      `,
      errors: [ruleError(3, 10, 'alwaysNullish')],
    },
    {
      code: `
function test(a: never) {
  return a ?? 'default';
}
      `,
      errors: [ruleError(3, 10, 'never')],
    },

    // Predicate functions
    {
      options: [{ checkArrayPredicates: true }],
      code: `
[1, 3, 5].filter(() => true);
[1, 2, 3].find(() => {
  return false;
});

// with non-literal array
function nothing(x: string[]) {
  return x.filter(() => false);
}
// with readonly array
function nothing2(x: readonly string[]) {
  return x.filter(() => false);
}
// with tuple
function nothing3(x: [string, string]) {
  return x.filter(() => false);
}
      `,
      errors: [
        ruleError(2, 24, 'alwaysTruthy'),
        ruleError(4, 10, 'alwaysFalsy'),
        ruleError(9, 25, 'alwaysFalsy'),
        ruleError(13, 25, 'alwaysFalsy'),
        ruleError(17, 25, 'alwaysFalsy'),
      ],
    },
    // Indexing cases
    {
      // This is an error because 'dict' doesn't represent
      //  the potential for undefined in its types
      code: `
declare const dict: Record<string, object>;
if (dict['mightNotExist']) {
}
      `,
      errors: [ruleError(3, 5, 'alwaysTruthy')],
    },
    {
      // Should still check tuples when accessed with literal numbers, since they don't have
      //   unsound index signatures
      code: `
const x = [{}] as [{ foo: string }];
if (x[0]) {
}
if (x[0]?.foo) {
}
      `,
      errors: [
        ruleError(3, 5, 'alwaysTruthy'),
        ruleError(5, 9, 'neverOptionalChain'),
      ],
    },
    {
      // Shouldn't mistake this for an array indexing case
      code: `
declare const arr: object[];
if (arr.filter) {
}
      `,
      errors: [ruleError(3, 5, 'alwaysTruthy')],
    },
    {
      options: [{ checkArrayPredicates: true }],
      code: `
function truthy() {
  return [];
}
function falsy() {}
[1, 3, 5].filter(truthy);
[1, 2, 3].find(falsy);
      `,
      errors: [
        ruleError(6, 18, 'alwaysTruthyFunc'),
        ruleError(7, 16, 'alwaysFalsyFunc'),
      ],
    },
    // Supports generics
    // TODO: fix this
    //     {
    //       options: [{ checkArrayPredicates: true }],
    //       code: `
    // const isTruthy = <T>(t: T) => T;
    // // Valid: numbers can be truthy or falsy (0).
    // [0,1,2,3].filter(isTruthy);
    // // Invalid: arrays are always falsy.
    // [[1,2], [3,4]].filter(isTruthy);
    // `,
    //       errors: [ruleError(6, 23, 'alwaysTruthyFunc')],
    //     },
    {
      code: `
while (true) {}
for (; true; ) {}
do {} while (true);
      `,
      options: [{ allowConstantLoopConditions: false }],
      errors: [
        ruleError(2, 8, 'alwaysTruthy'),
        ruleError(3, 8, 'alwaysTruthy'),
        ruleError(4, 14, 'alwaysTruthy'),
      ],
    },
    {
      code: noFormat`
let foo = { bar: true };
foo?.bar;
foo ?. bar;
foo ?.
  bar;
foo
  ?. bar;
      `,
      output: noFormat`
let foo = { bar: true };
foo.bar;
foo . bar;
foo .
  bar;
foo
  . bar;
      `,
      errors: [
        {
          messageId: 'neverOptionalChain',
          line: 3,
          column: 4,
          endLine: 3,
          endColumn: 6,
        },
        {
          messageId: 'neverOptionalChain',
          line: 4,
          column: 5,
          endLine: 4,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 5,
          column: 5,
          endLine: 5,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 8,
          column: 3,
          endLine: 8,
          endColumn: 5,
        },
      ],
    },
    {
      code: noFormat`
let foo = () => {};
foo?.();
foo ?. ();
foo ?.
  ();
foo
  ?. ();
      `,
      output: `
let foo = () => {};
foo();
foo  ();
foo${' '}
  ();
foo
   ();
      `,
      errors: [
        {
          messageId: 'neverOptionalChain',
          line: 3,
          column: 4,
          endLine: 3,
          endColumn: 6,
        },
        {
          messageId: 'neverOptionalChain',
          line: 4,
          column: 5,
          endLine: 4,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 5,
          column: 5,
          endLine: 5,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 8,
          column: 3,
          endLine: 8,
          endColumn: 5,
        },
      ],
    },
    {
      code: noFormat`
let foo = () => {};
foo?.(bar);
foo ?. (bar);
foo ?.
  (bar);
foo
  ?. (bar);
      `,
      output: `
let foo = () => {};
foo(bar);
foo  (bar);
foo${' '}
  (bar);
foo
   (bar);
      `,
      errors: [
        {
          messageId: 'neverOptionalChain',
          line: 3,
          column: 4,
          endLine: 3,
          endColumn: 6,
        },
        {
          messageId: 'neverOptionalChain',
          line: 4,
          column: 5,
          endLine: 4,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 5,
          column: 5,
          endLine: 5,
          endColumn: 7,
        },
        {
          messageId: 'neverOptionalChain',
          line: 8,
          column: 3,
          endLine: 8,
          endColumn: 5,
        },
      ],
    },
    {
      code: 'const foo = [1, 2, 3]?.[0];',
      output: 'const foo = [1, 2, 3][0];',
      errors: [
        {
          messageId: 'neverOptionalChain',
          line: 1,
          endLine: 1,
          column: 22,
          endColumn: 24,
        },
      ],
    },
  ],
});