typescript/switch-exhaustiveness-check Pedantic
What it does
This rule requires switch statements to be exhaustive when switching on union types.
Why is this bad?
When switching on a union type, it's important to handle all possible cases to avoid runtime errors. TypeScript can help ensure exhaustiveness, but only if the switch statement is properly structured with a default case that TypeScript can analyze.
Examples
Examples of incorrect code for this rule:
type Status = "pending" | "approved" | "rejected";
function handleStatus(status: Status) {
switch (status) {
case "pending":
return "Waiting for approval";
case "approved":
return "Request approved";
// Missing 'rejected' case
}
}
enum Color {
Red,
Green,
Blue,
}
function getColorName(color: Color) {
switch (color) {
case Color.Red:
return "red";
case Color.Green:
return "green";
// Missing Color.Blue case
}
}Examples of correct code for this rule:
type Status = "pending" | "approved" | "rejected";
function handleStatus(status: Status) {
switch (status) {
case "pending":
return "Waiting for approval";
case "approved":
return "Request approved";
case "rejected":
return "Request rejected";
}
}
// Or with default case for exhaustiveness checking
function handleStatusWithDefault(status: Status) {
switch (status) {
case "pending":
return "Waiting for approval";
case "approved":
return "Request approved";
case "rejected":
return "Request rejected";
default:
const _exhaustiveCheck: never = status;
return _exhaustiveCheck;
}
}
enum Color {
Red,
Green,
Blue,
}
function getColorName(color: Color) {
switch (color) {
case Color.Red:
return "red";
case Color.Green:
return "green";
case Color.Blue:
return "blue";
default:
const _exhaustiveCheck: never = color;
return _exhaustiveCheck;
}
}Configuration
This rule accepts a configuration object with the following properties:
allowDefaultCaseForExhaustiveSwitch
type: boolean
default: true
Whether to allow default cases on switches that are not exhaustive. When false, requires exhaustive switch statements without default cases.
considerDefaultExhaustiveForUnions
type: boolean
default: false
Whether to consider default cases exhaustive for union types. When true, a switch statement with a default case is considered exhaustive even if not all union members are handled explicitly.
defaultCaseCommentPattern
type: string | null
Regular expression pattern that when matched in a default case comment, will suppress the exhaustiveness check. Example: "@skip-exhaustive-check" to allow default: // @skip-exhaustive-check
requireDefaultForNonUnion
type: boolean
default: false
Whether to require default cases on switches over union types that are not exhaustive. When true, switches with non-exhaustive union types must have a default case.
How to use
To enable this rule using the config file or in the CLI, you can use:
{
"rules": {
"typescript/switch-exhaustiveness-check": "error"
}
}oxlint --type-aware --deny typescript/switch-exhaustiveness-check