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feat(eslint-plugin): [no-mixed-enums] add rule (#6102)
* feat(eslint-plugin): [no-mixed-enums] add rule * Fixed test formatting * Fixed config * Fixed description too * Snazzier query * Account for enum merging * Avoided the type checker where possible (mostly) * Added more type coverage * Apply suggestions from code review Co-authored-by: Brad Zacher <brad.zacher@gmail.com> * Use our own enum for AllowedType * Simplify to Number * Simplify to Number even further --------- Co-authored-by: Brad Zacher <brad.zacher@gmail.com>
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--- | ||
description: 'Disallow enums from having both number and string members.' | ||
--- | ||
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> 🛑 This file is source code, not the primary documentation location! 🛑 | ||
> | ||
> See **https://typescript-eslint.io/rules/no-mixed-enums** for documentation. | ||
TypeScript enums are allowed to assign numeric or string values to their members. | ||
Most enums contain either all numbers or all strings, but in theory you can mix-and-match within the same enum. | ||
Mixing enum member types is generally considered confusing and a bad practice. | ||
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## Examples | ||
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<!--tabs--> | ||
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### ❌ Incorrect | ||
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```ts | ||
enum Status { | ||
Unknown, | ||
Closed = 1, | ||
Open = 'open', | ||
} | ||
``` | ||
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### ✅ Correct (Explicit Numbers) | ||
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```ts | ||
enum Status { | ||
Unknown = 0, | ||
Closed = 1, | ||
Open = 2, | ||
} | ||
``` | ||
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### ✅ Correct (Implicit Numbers) | ||
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```ts | ||
enum Status { | ||
Unknown, | ||
Closed, | ||
Open, | ||
} | ||
``` | ||
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### ✅ Correct (Strings) | ||
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```ts | ||
enum Status { | ||
Unknown = 'unknown', | ||
Closed = 'closed', | ||
Open = 'open', | ||
} | ||
``` | ||
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## Iteration Pitfalls of Mixed Enum Member Values | ||
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Enum values may be iterated over using `Object.entries`/`Object.keys`/`Object.values`. | ||
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If all enum members are strings, the number of items will match the number of enum members: | ||
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```ts | ||
enum Status { | ||
Closed = 'closed', | ||
Open = 'open', | ||
} | ||
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// ['closed', 'open'] | ||
Object.values(Status); | ||
``` | ||
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But if the enum contains members that are initialized with numbers -including implicitly initialized numbers— then iteration over that enum will include those numbers as well: | ||
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```ts | ||
enum Status { | ||
Unknown, | ||
Closed = 1, | ||
Open = 'open', | ||
} | ||
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// ["Unknown", "Closed", 0, 1, "open"] | ||
Object.values(Status); | ||
``` | ||
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## When Not To Use It | ||
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If you don't mind the confusion of mixed enum member values and don't iterate over enums, you can safely disable this rule. |
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import type { Scope } from '@typescript-eslint/scope-manager'; | ||
import { DefinitionType } from '@typescript-eslint/scope-manager'; | ||
import type { TSESTree } from '@typescript-eslint/utils'; | ||
import { AST_NODE_TYPES } from '@typescript-eslint/utils'; | ||
import * as tsutils from 'tsutils'; | ||
import * as ts from 'typescript'; | ||
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import * as util from '../util'; | ||
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enum AllowedType { | ||
Number, | ||
String, | ||
Unknown, | ||
} | ||
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export default util.createRule({ | ||
name: 'no-mixed-enums', | ||
meta: { | ||
docs: { | ||
description: 'Disallow enums from having both number and string members', | ||
recommended: 'strict', | ||
requiresTypeChecking: true, | ||
}, | ||
messages: { | ||
mixed: `Mixing number and string enums can be confusing.`, | ||
}, | ||
schema: [], | ||
type: 'problem', | ||
}, | ||
defaultOptions: [], | ||
create(context) { | ||
const parserServices = util.getParserServices(context); | ||
const typeChecker = parserServices.program.getTypeChecker(); | ||
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interface CollectedDefinitions { | ||
imports: TSESTree.Node[]; | ||
previousSibling: TSESTree.TSEnumDeclaration | undefined; | ||
} | ||
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function collectNodeDefinitions( | ||
node: TSESTree.TSEnumDeclaration, | ||
): CollectedDefinitions { | ||
const { name } = node.id; | ||
const found: CollectedDefinitions = { | ||
imports: [], | ||
previousSibling: undefined, | ||
}; | ||
let scope: Scope | null = context.getScope(); | ||
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for (const definition of scope.upper?.set.get(name)?.defs ?? []) { | ||
if ( | ||
definition.node.type === AST_NODE_TYPES.TSEnumDeclaration && | ||
definition.node.range[0] < node.range[0] && | ||
definition.node.members.length > 0 | ||
) { | ||
found.previousSibling = definition.node; | ||
break; | ||
} | ||
} | ||
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while (scope) { | ||
scope.set.get(name)?.defs?.forEach(definition => { | ||
if (definition.type === DefinitionType.ImportBinding) { | ||
found.imports.push(definition.node); | ||
} | ||
}); | ||
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scope = scope.upper; | ||
} | ||
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return found; | ||
} | ||
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function getAllowedTypeForNode(node: ts.Node): AllowedType { | ||
return tsutils.isTypeFlagSet( | ||
typeChecker.getTypeAtLocation(node), | ||
ts.TypeFlags.StringLike, | ||
) | ||
? AllowedType.String | ||
: AllowedType.Number; | ||
} | ||
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function getTypeFromImported( | ||
imported: TSESTree.Node, | ||
): AllowedType | undefined { | ||
const type = typeChecker.getTypeAtLocation( | ||
parserServices.esTreeNodeToTSNodeMap.get(imported), | ||
); | ||
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const valueDeclaration = type.getSymbol()?.valueDeclaration; | ||
if ( | ||
!valueDeclaration || | ||
!ts.isEnumDeclaration(valueDeclaration) || | ||
valueDeclaration.members.length === 0 | ||
) { | ||
return undefined; | ||
} | ||
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return getAllowedTypeForNode(valueDeclaration.members[0]); | ||
} | ||
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function getMemberType(member: TSESTree.TSEnumMember): AllowedType { | ||
if (!member.initializer) { | ||
return AllowedType.Number; | ||
} | ||
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switch (member.initializer.type) { | ||
case AST_NODE_TYPES.Literal: | ||
switch (typeof member.initializer.value) { | ||
case 'number': | ||
return AllowedType.Number; | ||
case 'string': | ||
return AllowedType.String; | ||
default: | ||
return AllowedType.Unknown; | ||
} | ||
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case AST_NODE_TYPES.TemplateLiteral: | ||
return AllowedType.String; | ||
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default: | ||
return getAllowedTypeForNode( | ||
parserServices.esTreeNodeToTSNodeMap.get(member.initializer), | ||
); | ||
} | ||
} | ||
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function getDesiredTypeForDefinition( | ||
node: TSESTree.TSEnumDeclaration, | ||
): AllowedType | ts.TypeFlags.Unknown | undefined { | ||
const { imports, previousSibling } = collectNodeDefinitions(node); | ||
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// Case: Merged ambiently via module augmentation | ||
// import { MyEnum } from 'other-module'; | ||
// declare module 'other-module' { | ||
// enum MyEnum { A } | ||
// } | ||
for (const imported of imports) { | ||
const typeFromImported = getTypeFromImported(imported); | ||
if (typeFromImported !== undefined) { | ||
return typeFromImported; | ||
} | ||
} | ||
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// Case: Multiple enum declarations in the same file | ||
// enum MyEnum { A } | ||
// enum MyEnum { B } | ||
if (previousSibling) { | ||
return getMemberType(previousSibling.members[0]); | ||
} | ||
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// Case: Namespace declaration merging | ||
// namespace MyNamespace { | ||
// export enum MyEnum { A } | ||
// } | ||
// namespace MyNamespace { | ||
// export enum MyEnum { B } | ||
// } | ||
if ( | ||
node.parent!.type === AST_NODE_TYPES.ExportNamedDeclaration && | ||
node.parent!.parent!.type === AST_NODE_TYPES.TSModuleBlock | ||
) { | ||
// TODO: We don't need to dip into the TypeScript type checker here! | ||
// Merged namespaces must all exist in the same file. | ||
// We could instead compare this file's nodes to find the merges. | ||
const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node.id); | ||
const declarations = typeChecker | ||
.getSymbolAtLocation(tsNode)! | ||
.getDeclarations()!; | ||
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for (const declaration of declarations) { | ||
for (const member of (declaration as ts.EnumDeclaration).members) { | ||
return member.initializer | ||
? tsutils.isTypeFlagSet( | ||
typeChecker.getTypeAtLocation(member.initializer), | ||
ts.TypeFlags.StringLike, | ||
) | ||
? AllowedType.String | ||
: AllowedType.Number | ||
: AllowedType.Number; | ||
} | ||
} | ||
} | ||
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// Finally, we default to the type of the first enum member | ||
return getMemberType(node.members[0]); | ||
} | ||
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return { | ||
TSEnumDeclaration(node): void { | ||
if (!node.members.length) { | ||
return; | ||
} | ||
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let desiredType = getDesiredTypeForDefinition(node); | ||
if (desiredType === ts.TypeFlags.Unknown) { | ||
return; | ||
} | ||
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for (const member of node.members) { | ||
const currentType = getMemberType(member); | ||
if (currentType === AllowedType.Unknown) { | ||
return; | ||
} | ||
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if (currentType === AllowedType.Number) { | ||
desiredType ??= currentType; | ||
} | ||
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if ( | ||
currentType !== desiredType && | ||
(currentType !== undefined || desiredType === AllowedType.String) | ||
) { | ||
context.report({ | ||
messageId: 'mixed', | ||
node: member.initializer ?? member, | ||
}); | ||
return; | ||
} | ||
} | ||
}, | ||
}; | ||
}, | ||
}); |
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