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fix(eslint-plugin): [switch-exhaustiveness-check] fix new allowDefaul…
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…tCaseForExhaustiveSwitch option (#8176)

* fix(allowDefaultCaseForExhaustiveSwitch): rule

* chore: format

* fix: add containsNonLiteralType

* chore: cleanup

* refactor: use type flags instead of strings

* Update packages/eslint-plugin/src/rules/switch-exhaustiveness-check.ts

* Update packages/eslint-plugin/src/rules/switch-exhaustiveness-check.ts

---------

Co-authored-by: Josh Goldberg ✨ <git@joshuakgoldberg.com>
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@Zamiell @JoshuaKGoldberg
Zamiell and JoshuaKGoldberg committed Jan 8, 2024
1 parent 3a219c0 commit 5205192
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Showing 2 changed files with 323 additions and 3 deletions.
41 changes: 38 additions & 3 deletions packages/eslint-plugin/src/rules/switch-exhaustiveness-check.ts
View file
Expand Up @@ -17,12 +17,14 @@ interface SwitchMetadata {
readonly missingBranchTypes: ts.Type[];
readonly defaultCase: TSESTree.SwitchCase | undefined;
readonly isUnion: boolean;
readonly containsNonLiteralType: boolean;
}

type Options = [
{
/**
* If `true`, allow `default` cases on switch statements with exhaustive cases.
* If `true`, allow `default` cases on switch statements with exhaustive
* cases.
*
* @default true
*/
Expand Down Expand Up @@ -104,12 +106,16 @@ export default createRule<Options, MessageIds>({
| string
| undefined;

const containsNonLiteralType =
doesTypeContainNonLiteralType(discriminantType);

if (!discriminantType.isUnion()) {
return {
symbolName,
missingBranchTypes: [],
defaultCase,
isUnion: false,
containsNonLiteralType,
};
}

Expand Down Expand Up @@ -138,9 +144,29 @@ export default createRule<Options, MessageIds>({
missingBranchTypes,
defaultCase,
isUnion: true,
containsNonLiteralType,
};
}

/**
* For example:
*
* - `"foo" | "bar"` is a type with all literal types.
* - `"foo" | number` is a type that contains non-literal types.
*
* Default cases are never superfluous in switches with non-literal types.
*/
function doesTypeContainNonLiteralType(type: ts.Type): boolean {
const types = tsutils.unionTypeParts(type);
return types.some(
type =>
!isFlagSet(
type.getFlags(),
ts.TypeFlags.Literal | ts.TypeFlags.Undefined | ts.TypeFlags.Null,
),
);
}

function checkSwitchExhaustive(
node: TSESTree.SwitchStatement,
switchMetadata: SwitchMetadata,
Expand Down Expand Up @@ -272,9 +298,14 @@ export default createRule<Options, MessageIds>({
return;
}

const { missingBranchTypes, defaultCase } = switchMetadata;
const { missingBranchTypes, defaultCase, containsNonLiteralType } =
switchMetadata;

if (missingBranchTypes.length === 0 && defaultCase !== undefined) {
if (
missingBranchTypes.length === 0 &&
defaultCase !== undefined &&
!containsNonLiteralType
) {
context.report({
node: defaultCase,
messageId: 'dangerousDefaultCase',
Expand Down Expand Up @@ -322,3 +353,7 @@ export default createRule<Options, MessageIds>({
};
},
});

function isFlagSet(flags: number, flag: number): boolean {
return (flags & flag) !== 0;
}
285 changes: 285 additions & 0 deletions packages/eslint-plugin/tests/rules/switch-exhaustiveness-check.test.ts
View file
Expand Up @@ -229,6 +229,110 @@ switch (value) {
},
],
},
// switch with default clause on string type +
// "allowDefaultCaseForExhaustiveSwitch" option
{
code: `
declare const value: string;
switch (value) {
case 'foo':
return 0;
case 'bar':
return 1;
default:
return -1;
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
},
// switch with default clause on number type +
// "allowDefaultCaseForExhaustiveSwitch" option
{
code: `
declare const value: number;
switch (value) {
case 0:
return 0;
case 1:
return 1;
default:
return -1;
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
},
// switch with default clause on bigint type +
// "allowDefaultCaseForExhaustiveSwitch" option
{
code: `
declare const value: bigint;
switch (value) {
case 0:
return 0;
case 1:
return 1;
default:
return -1;
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
},
// switch with default clause on symbol type +
// "allowDefaultCaseForExhaustiveSwitch" option
{
code: `
declare const value: symbol;
const foo = Symbol('foo');
switch (value) {
case foo:
return 0;
default:
return -1;
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
},
// switch with default clause on union with number +
// "allowDefaultCaseForExhaustiveSwitch" option
{
code: `
declare const value: 0 | 1 | number;
switch (value) {
case 0:
return 0;
case 1:
return 1;
default:
return -1;
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
},
],
invalid: [
{
Expand Down Expand Up @@ -735,6 +839,7 @@ switch (value) {
],
},
{
// superfluous switch with a string-based union
code: `
type MyUnion = 'foo' | 'bar' | 'baz';
Expand All @@ -746,6 +851,186 @@ switch (myUnion) {
case 'baz': {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with a string-based enum
code: `
enum MyEnum {
Foo = 'Foo',
Bar = 'Bar',
Baz = 'Baz',
}
declare const myEnum: MyEnum;
switch (myEnum) {
case MyEnum.Foo:
case MyEnum.Bar:
case MyEnum.Baz: {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with a number-based enum
code: `
enum MyEnum {
Foo,
Bar,
Baz,
}
declare const myEnum: MyEnum;
switch (myEnum) {
case MyEnum.Foo:
case MyEnum.Bar:
case MyEnum.Baz: {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with a boolean
code: `
declare const myBoolean: boolean;
switch (myBoolean) {
case true:
case false: {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with undefined
code: `
declare const myValue: undefined;
switch (myValue) {
case undefined: {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with null
code: `
declare const myValue: null;
switch (myValue) {
case null: {
break;
}
default: {
break;
}
}
`,
options: [
{
allowDefaultCaseForExhaustiveSwitch: false,
requireDefaultForNonUnion: false,
},
],
errors: [
{
messageId: 'dangerousDefaultCase',
},
],
},
{
// superfluous switch with union of various types
code: `
declare const myValue: 'foo' | boolean | undefined | null;
switch (myValue) {
case 'foo':
case true:
case false:
case undefined:
case null: {
break;
}
default: {
break;
}
Expand Down

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