useExhaustiveSwitchCases

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JavaScript (and super languages)

Summary

Rule available since: v2.0.0
Diagnostic Category: lint/nursery/useExhaustiveSwitchCases
This rule has an unsafe fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- project
Sources:
- Same as @typescript-eslint/switch-exhaustiveness-check

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "useExhaustiveSwitchCases": "error"
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      }
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    }
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  }
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}

Description

Require switch-case statements to be exhaustive.

When working with union types in TypeScript, it’s common to want to write a switch statement intended to contain a case for each possible variant. However, if the union type changes, it’s easy to forget to modify the cases to account for any new types.

This rule reports when a switch statement over a value typed as a union of literals lacks a case for any of those literal types and does not have a default clause.

Examples

Invalid

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type Day =
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  | 'Monday'
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  | 'Tuesday'
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  | 'Wednesday'
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  | 'Thursday'
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  | 'Friday'
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  | 'Saturday'
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  | 'Sunday';
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declare const day: Day;
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let result = 0;
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switch (day) {
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  case 'Monday':
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    result = 1;
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    break;
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}

/invalid.ts:13:1 lint/nursery/useExhaustiveSwitchCases  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The switch statement is not exhaustive.
  
    11 │ let result = 0;
    12 │ 
  > 13 │ switch (day) {
       │ ^^^^^^^^^^^^^^
  > 14 │   case ‘Monday’:
  > 15 │     result = 1;
  > 16 │     break;
  > 17 │ }
       │ ^
    18 │ 
  
  ℹ Some variants of the union type are not handled here.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ These cases are missing:
  
  - “Tuesday”
  - “Wednesday”
  - “Thursday”
  - “Friday”
  - “Saturday”
  - “Sunday”
  
  ℹ Unsafe fix: Add the missing cases to the switch statement.
  
    14 14 │     case ‘Monday’:
    15 15 │       result = 1;
    16    │ - ····break;
       16 │ + ····break;
       17 │ + ··case·“Tuesday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
       18 │ + ··case·“Wednesday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
       19 │ + ··case·“Thursday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
       20 │ + ··case·“Friday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
       21 │ + ··case·“Saturday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
       22 │ + ··case·“Sunday”:·throw·new·Error(“TODO:·Not·implemented·yet”);
    17 23 │   }
    18 24 │

Valid

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type Day =
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  | 'Monday'
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  | 'Tuesday'
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  | 'Wednesday'
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  | 'Thursday'
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  | 'Friday'
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  | 'Saturday'
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  | 'Sunday';
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declare const day: Day;
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let result = 0;
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switch (day) {
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  case 'Monday':
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    result = 1;
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    break;
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  case 'Tuesday':
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    result = 2;
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    break;
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  case 'Wednesday':
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    result = 3;
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    break;
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  case 'Thursday':
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    result = 4;
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    break;
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  case 'Friday':
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    result = 5;
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    break;
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  case 'Saturday':
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    result = 6;
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    break;
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  case 'Sunday':
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    result = 7;
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    break;
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}