switch-exhaustiveness-check.test.ts

import path from 'path';
import switchExhaustivenessCheck from '../../src/rules/switch-exhaustiveness-check';
import { RuleTester, noFormat } from '../RuleTester';

const rootPath = path.join(process.cwd(), 'tests/fixtures/');

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

ruleTester.run('switch-exhaustiveness-check', switchExhaustivenessCheck, {
  valid: [
    // All branches matched
    `
type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

const day = 'Monday' as Day;
let result = 0;

switch (day) {
  case 'Monday': {
    result = 1;
    break;
  }
  case 'Tuesday': {
    result = 2;
    break;
  }
  case 'Wednesday': {
    result = 3;
    break;
  }
  case 'Thursday': {
    result = 4;
    break;
  }
  case 'Friday': {
    result = 5;
    break;
  }
  case 'Saturday': {
    result = 6;
    break;
  }
  case 'Sunday': {
    result = 7;
    break;
  }
}
    `,
    // Other primitive literals work too
    `
type Num = 0 | 1 | 2;

function test(value: Num): number {
  switch (value) {
    case 0:
      return 0;
    case 1:
      return 1;
    case 2:
      return 2;
  }
}
    `,
    `
type Bool = true | false;

function test(value: Bool): number {
  switch (value) {
    case true:
      return 1;
    case false:
      return 0;
  }
}
    `,
    `
type Mix = 0 | 1 | 'two' | 'three' | true;

function test(value: Mix): number {
  switch (value) {
    case 0:
      return 0;
    case 1:
      return 1;
    case 'two':
      return 2;
    case 'three':
      return 3;
    case true:
      return 4;
  }
}
    `,
    // Works with type references
    `
type A = 'a';
type B = 'b';
type C = 'c';
type Union = A | B | C;

function test(value: Union): number {
  switch (value) {
    case 'a':
      return 1;
    case 'b':
      return 2;
    case 'c':
      return 3;
  }
}
    `,
    // Works with `typeof`
    `
const A = 'a';
const B = 1;
const C = true;

type Union = typeof A | typeof B | typeof C;

function test(value: Union): number {
  switch (value) {
    case 'a':
      return 1;
    case 1:
      return 2;
    case true:
      return 3;
  }
}
    `,
    // Switch contains default clause.
    `
type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

const day = 'Monday' as Day;
let result = 0;

switch (day) {
  case 'Monday': {
    result = 1;
    break;
  }
  default: {
    result = 42;
  }
}
    `,
    // Exhaustiveness check only works for union types...
    `
const day = 'Monday' as string;
let result = 0;

switch (day) {
  case 'Monday': {
    result = 1;
    break;
  }
  case 'Tuesday': {
    result = 2;
    break;
  }
}
    `,
    // ... and enums (at least for now).
    `
enum Enum {
  A,
  B,
}

function test(value: Enum): number {
  switch (value) {
    case Enum.A:
      return 1;
    case Enum.B:
      return 2;
  }
}
    `,
    // Object union types won't work either, unless it's a discriminated union
    `
type ObjectUnion = { a: 1 } | { b: 2 };

function test(value: ObjectUnion): number {
  switch (value.a) {
    case 1:
      return 1;
  }
}
    `,
  ],
  invalid: [
    {
      // Matched only one branch out of seven.
      code: `
type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

const day = 'Monday' as Day;
let result = 0;

switch (day) {
  case 'Monday': {
    result = 1;
    break;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 14,
          column: 9,
          data: {
            missingBranches:
              '"Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday"',
          },
        },
      ],
    },
    {
      // Didn't match all enum variants
      code: `
enum Enum {
  A,
  B,
}

function test(value: Enum): number {
  switch (value) {
    case Enum.A:
      return 1;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 8,
          column: 11,
          data: {
            missingBranches: 'Enum.B',
          },
        },
      ],
    },
    {
      code: `
type A = 'a';
type B = 'b';
type C = 'c';
type Union = A | B | C;

function test(value: Union): number {
  switch (value) {
    case 'a':
      return 1;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 8,
          column: 11,
          data: {
            missingBranches: '"b" | "c"',
          },
        },
      ],
    },
    {
      code: `
const A = 'a';
const B = 1;
const C = true;

type Union = typeof A | typeof B | typeof C;

function test(value: Union): number {
  switch (value) {
    case 'a':
      return 1;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 9,
          column: 11,
          data: {
            missingBranches: 'true | 1',
          },
        },
      ],
    },
    {
      code: `
type DiscriminatedUnion = { type: 'A'; a: 1 } | { type: 'B'; b: 2 };

function test(value: DiscriminatedUnion): number {
  switch (value.type) {
    case 'A':
      return 1;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 5,
          column: 11,
          data: {
            missingBranches: '"B"',
          },
        },
      ],
    },
    {
      // Still complains with empty switch
      code: `
type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

const day = 'Monday' as Day;

switch (day) {
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 13,
          column: 9,
          data: {
            missingBranches:
              '"Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday"',
          },
        },
      ],
    },
    {
      // Still complains with union intersection part
      code: `
type FooBar = (string & { foo: void }) | 'bar';

const foobar = 'bar' as FooBar;
let result = 0;

switch (foobar) {
  case 'bar': {
    result = 42;
    break;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 7,
          column: 9,
          data: {
            missingBranches: 'string & { foo: void; }',
          },
        },
      ],
    },
    {
      code: `
const a = Symbol('a');
const b = Symbol('b');
const c = Symbol('c');

type T = typeof a | typeof b | typeof c;

function test(value: T): number {
  switch (value) {
    case a:
      return 1;
  }
}
      `,
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          line: 9,
          column: 11,
          data: {
            missingBranches: 'typeof b | typeof c',
          },
        },
      ],
    },
    // Provides suggestions to add missing cases
    {
      // with existing cases present
      code: `
type T = 1 | 2;

function test(value: T): number {
  switch (value) {
    case 1:
      return 1;
  }
}
      `.trimRight(),
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          suggestions: [
            {
              messageId: 'addMissingCases',
              output: noFormat`
type T = 1 | 2;

function test(value: T): number {
  switch (value) {
    case 1:
      return 1;
    case 2: { throw new Error('Not implemented yet: 2 case') }
  }
}
              `.trimRight(),
            },
          ],
        },
      ],
    },
    {
      // without existing cases
      code: `
type T = 1 | 2;

function test(value: T): number {
  switch (value) {
  }
}
      `.trimRight(),
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          suggestions: [
            {
              messageId: 'addMissingCases',
              output: noFormat`
type T = 1 | 2;

function test(value: T): number {
  switch (value) {
  case 1: { throw new Error('Not implemented yet: 1 case') }
  case 2: { throw new Error('Not implemented yet: 2 case') }
  }
}
              `.trimRight(),
            },
          ],
        },
      ],
    },
    {
      // keys include special characters
      code: `
export enum Enum {
  'test-test' = 'test-test',
  'test' = 'test',
}

function test(arg: Enum): string {
  switch (arg) {
  }
}
      `.trimRight(),
      errors: [
        {
          messageId: 'switchIsNotExhaustive',
          suggestions: [
            {
              messageId: 'addMissingCases',
              output: noFormat`
export enum Enum {
  'test-test' = 'test-test',
  'test' = 'test',
}

function test(arg: Enum): string {
  switch (arg) {
  case Enum['test-test']: { throw new Error('Not implemented yet: Enum['test-test'] case') }
  case Enum.test: { throw new Error('Not implemented yet: Enum.test case') }
  }
}
              `.trimRight(),
            },
          ],
        },
      ],
    },
  ],
});