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feat(eslint-plugin): added new rule use-default-type-parameter (#562)
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packages/eslint-plugin/docs/rules/no-unnecessary-type-arguments.md
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# Enforces that types will not to be used (no-unnecessary-type-arguments) | ||
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Warns if an explicitly specified type argument is the default for that type parameter. | ||
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## Rule Details | ||
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Type parameters in TypeScript may specify a default value. | ||
For example: | ||
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```ts | ||
function f<T = number>() {} | ||
``` | ||
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It is redundant to provide an explicit type parameter equal to that default. | ||
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Examples of **incorrect** code for this rule: | ||
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```ts | ||
function f<T = number>() {} | ||
f<number>(); | ||
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function g<T = number, U = string>() {} | ||
g<string, string>(); | ||
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class C<T = number> {} | ||
function h(c: C<number>) {} | ||
new C<number>(); | ||
class D extends C<number> {} | ||
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interface I<T = number> {} | ||
class Impl implements I<number> {} | ||
``` | ||
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Examples of **correct** code for this rule: | ||
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```ts | ||
function f<T = number>() {} | ||
f<string>(); | ||
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function g<T = number, U = string>() {} | ||
g<number, number>(); | ||
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class C<T = number> {} | ||
new C<string>(); | ||
class D extends C<string> {} | ||
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interface I<T = number> {} | ||
class Impl implements I<string> {} | ||
``` | ||
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## Related to | ||
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- TSLint: [use-default-type-parameter](https://palantir.github.io/tslint/rules/use-default-type-parameter) |
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159
packages/eslint-plugin/src/rules/no-unnecessary-type-arguments.ts
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import { TSESTree } from '@typescript-eslint/experimental-utils'; | ||
import * as tsutils from 'tsutils'; | ||
import ts from 'typescript'; | ||
import * as util from '../util'; | ||
import { findFirstResult } from '../util'; | ||
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interface ArgsAndParams { | ||
typeArguments: ts.NodeArray<ts.TypeNode>; | ||
typeParameters: readonly ts.TypeParameterDeclaration[]; | ||
} | ||
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type ExtendingClassLikeDeclaration = ts.ClassLikeDeclaration & { | ||
heritageClauses: ts.NodeArray<ts.HeritageClause>; | ||
}; | ||
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type ParameterCapableTSNode = | ||
| ts.CallExpression | ||
| ts.NewExpression | ||
| ts.TypeReferenceNode | ||
| ts.ExpressionWithTypeArguments; | ||
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type MessageIds = 'unnecessaryTypeParameter'; | ||
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export default util.createRule<[], MessageIds>({ | ||
name: 'no-unnecessary-type-arguments', | ||
meta: { | ||
docs: { | ||
description: | ||
'Warns if an explicitly specified type argument is the default for that type parameter', | ||
category: 'Best Practices', | ||
recommended: false, | ||
}, | ||
fixable: 'code', | ||
messages: { | ||
unnecessaryTypeParameter: | ||
'This is the default value for this type parameter, so it can be omitted.', | ||
}, | ||
schema: [], | ||
type: 'suggestion', | ||
}, | ||
defaultOptions: [], | ||
create(context) { | ||
const parserServices = util.getParserServices(context); | ||
const checker = parserServices.program.getTypeChecker(); | ||
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function checkTSArgsAndParameters( | ||
esParameters: TSESTree.TSTypeParameterInstantiation, | ||
{ typeArguments, typeParameters }: ArgsAndParams, | ||
): void { | ||
// Just check the last one. Must specify previous type parameters if the last one is specified. | ||
const i = typeArguments.length - 1; | ||
const arg = typeArguments[i]; | ||
const param = typeParameters[i]; | ||
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// TODO: would like checker.areTypesEquivalent. https://github.com/Microsoft/TypeScript/issues/13502 | ||
if ( | ||
param.default === undefined || | ||
param.default.getText() !== arg.getText() | ||
) { | ||
return; | ||
} | ||
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context.report({ | ||
fix: fixer => | ||
fixer.removeRange( | ||
i === 0 | ||
? [typeArguments.pos - 1, typeArguments.end + 1] | ||
: [typeArguments[i - 1].end, arg.end], | ||
), | ||
messageId: 'unnecessaryTypeParameter', | ||
node: esParameters!.params[i], | ||
}); | ||
} | ||
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return { | ||
TSTypeParameterInstantiation(node) { | ||
const parentDeclaration = parserServices.esTreeNodeToTSNodeMap.get( | ||
node.parent!, | ||
) as ExtendingClassLikeDeclaration | ParameterCapableTSNode; | ||
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const expression = tsutils.isClassLikeDeclaration(parentDeclaration) | ||
? parentDeclaration.heritageClauses[0].types[0] | ||
: parentDeclaration; | ||
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const argsAndParams = getArgsAndParameters(expression, checker); | ||
if (argsAndParams !== undefined) { | ||
checkTSArgsAndParameters(node, argsAndParams); | ||
} | ||
}, | ||
}; | ||
}, | ||
}); | ||
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function getArgsAndParameters( | ||
node: ParameterCapableTSNode, | ||
checker: ts.TypeChecker, | ||
): ArgsAndParams | undefined { | ||
const typeParameters = getTypeParametersFromNode(node, checker); | ||
return typeParameters === undefined | ||
? undefined | ||
: { typeArguments: node.typeArguments!, typeParameters }; | ||
} | ||
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function getTypeParametersFromNode( | ||
node: ParameterCapableTSNode, | ||
checker: ts.TypeChecker, | ||
) { | ||
if (ts.isExpressionWithTypeArguments(node)) { | ||
return getTypeParametersFromType(node.expression, checker); | ||
} | ||
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if (ts.isTypeReferenceNode(node)) { | ||
return getTypeParametersFromType(node.typeName, checker); | ||
} | ||
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return getTypeParametersFromCall(node, checker); | ||
} | ||
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function getTypeParametersFromType( | ||
type: ts.EntityName | ts.Expression | ts.ClassDeclaration, | ||
checker: ts.TypeChecker, | ||
): readonly ts.TypeParameterDeclaration[] | undefined { | ||
const sym = getAliasedSymbol(checker.getSymbolAtLocation(type)!, checker); | ||
if (sym === undefined || sym.declarations === undefined) { | ||
return undefined; | ||
} | ||
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return findFirstResult(sym.declarations, decl => | ||
tsutils.isClassLikeDeclaration(decl) || | ||
ts.isTypeAliasDeclaration(decl) || | ||
ts.isInterfaceDeclaration(decl) | ||
? decl.typeParameters | ||
: undefined, | ||
); | ||
} | ||
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function getTypeParametersFromCall( | ||
node: ts.CallExpression | ts.NewExpression, | ||
checker: ts.TypeChecker, | ||
): readonly ts.TypeParameterDeclaration[] | undefined { | ||
const sig = checker.getResolvedSignature(node); | ||
const sigDecl = sig === undefined ? undefined : sig.getDeclaration(); | ||
if (sigDecl === undefined) { | ||
return ts.isNewExpression(node) | ||
? getTypeParametersFromType(node.expression, checker) | ||
: undefined; | ||
} | ||
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return sigDecl.typeParameters; | ||
} | ||
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function getAliasedSymbol( | ||
symbol: ts.Symbol, | ||
checker: ts.TypeChecker, | ||
): ts.Symbol | undefined { | ||
return tsutils.isSymbolFlagSet(symbol, ts.SymbolFlags.Alias) | ||
? checker.getAliasedSymbol(symbol) | ||
: symbol; | ||
} |
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