/
no-unnecessary-type-arguments.ts
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/
no-unnecessary-type-arguments.ts
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import { TSESTree } from '@typescript-eslint/experimental-utils';
import * as tsutils from 'tsutils';
import * as ts from 'typescript';
import * as util from '../util';
import { findFirstResult } from '../util';
type ParameterCapableTSNode =
| ts.TaggedTemplateExpression
| ts.ImportTypeNode
| ts.CallExpression
| ts.NewExpression
| ts.TypeReferenceNode
| ts.ExpressionWithTypeArguments
| ts.JsxOpeningElement
| ts.JsxSelfClosingElement;
type MessageIds = 'unnecessaryTypeParameter';
export default util.createRule<[], MessageIds>({
name: 'no-unnecessary-type-arguments',
meta: {
docs: {
description:
'Enforces that type arguments will not be used if not required',
category: 'Best Practices',
recommended: false,
requiresTypeChecking: true,
},
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();
const sourceCode = context.getSourceCode();
function checkTSArgsAndParameters(
esParameters: TSESTree.TSTypeParameterInstantiation,
typeParameters: readonly ts.TypeParameterDeclaration[],
): void {
// Just check the last one. Must specify previous type parameters if the last one is specified.
const i = esParameters.params.length - 1;
const arg = esParameters.params[i];
const param = typeParameters[i];
// TODO: would like checker.areTypesEquivalent. https://github.com/Microsoft/TypeScript/issues/13502
if (
!param.default ||
param.default.getText() !== sourceCode.getText(arg)
) {
return;
}
context.report({
node: arg,
messageId: 'unnecessaryTypeParameter',
fix: fixer =>
fixer.removeRange(
i === 0
? esParameters.range
: [esParameters.params[i - 1].range[1], arg.range[1]],
),
});
}
return {
TSTypeParameterInstantiation(node): void {
const expression = parserServices.esTreeNodeToTSNodeMap.get(node);
const typeParameters = getTypeParametersFromNode(expression, checker);
if (typeParameters) {
checkTSArgsAndParameters(node, typeParameters);
}
},
};
},
});
function getTypeParametersFromNode(
node: ParameterCapableTSNode,
checker: ts.TypeChecker,
): readonly ts.TypeParameterDeclaration[] | undefined {
if (ts.isExpressionWithTypeArguments(node)) {
return getTypeParametersFromType(node.expression, checker);
}
if (ts.isTypeReferenceNode(node)) {
return getTypeParametersFromType(node.typeName, checker);
}
if (ts.isCallExpression(node) || ts.isNewExpression(node)) {
return getTypeParametersFromCall(node, checker);
}
return undefined;
}
function getTypeParametersFromType(
type: ts.EntityName | ts.Expression | ts.ClassDeclaration,
checker: ts.TypeChecker,
): readonly ts.TypeParameterDeclaration[] | undefined {
const symAtLocation = checker.getSymbolAtLocation(type);
if (!symAtLocation) {
return undefined;
}
const sym = getAliasedSymbol(symAtLocation, checker);
if (!sym.declarations) {
return undefined;
}
return findFirstResult(sym.declarations, decl =>
tsutils.isClassLikeDeclaration(decl) ||
ts.isTypeAliasDeclaration(decl) ||
ts.isInterfaceDeclaration(decl)
? decl.typeParameters
: undefined,
);
}
function getTypeParametersFromCall(
node: ts.CallExpression | ts.NewExpression,
checker: ts.TypeChecker,
): readonly ts.TypeParameterDeclaration[] | undefined {
const sig = checker.getResolvedSignature(node);
const sigDecl = sig?.getDeclaration();
if (!sigDecl) {
return ts.isNewExpression(node)
? getTypeParametersFromType(node.expression, checker)
: undefined;
}
return sigDecl.typeParameters;
}
function getAliasedSymbol(
symbol: ts.Symbol,
checker: ts.TypeChecker,
): ts.Symbol {
return tsutils.isSymbolFlagSet(symbol, ts.SymbolFlags.Alias)
? checker.getAliasedSymbol(symbol)
: symbol;
}