@typescript-eslint/eslint-plugin/dist/rules/prefer-reduce-type-parameter.js

TypeScript plugin for ESLint

"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
const tsutils = __importStar(require("ts-api-utils"));
const util_1 = require("../util");
exports.default = (0, util_1.createRule)({
    name: 'prefer-reduce-type-parameter',
    meta: {
        type: 'problem',
        docs: {
            description: 'Enforce using type parameter when calling `Array#reduce` instead of using a type assertion',
            recommended: 'strict',
            requiresTypeChecking: true,
        },
        fixable: 'code',
        messages: {
            preferTypeParameter: 'Unnecessary assertion: Array#reduce accepts a type parameter for the default value.',
        },
        schema: [],
    },
    defaultOptions: [],
    create(context) {
        const services = (0, util_1.getParserServices)(context);
        const checker = services.program.getTypeChecker();
        function isArrayType(type) {
            return tsutils
                .unionTypeParts(type)
                .every(unionPart => tsutils
                .intersectionTypeParts(unionPart)
                .every(t => checker.isArrayType(t) || checker.isTupleType(t)));
        }
        return {
            'CallExpression > MemberExpression.callee'(callee) {
                if (!(0, util_1.isStaticMemberAccessOfValue)(callee, context, 'reduce')) {
                    return;
                }
                const [, secondArg] = callee.parent.arguments;
                if (callee.parent.arguments.length < 2) {
                    return;
                }
                if ((0, util_1.isTypeAssertion)(secondArg)) {
                    const initializerType = services.getTypeAtLocation(secondArg.expression);
                    const assertedType = services.getTypeAtLocation(secondArg.typeAnnotation);
                    const isAssertionNecessary = !checker.isTypeAssignableTo(initializerType, assertedType);
                    // don't report this if the resulting fix will be a type error
                    if (isAssertionNecessary) {
                        return;
                    }
                }
                else {
                    return;
                }
                // Get the symbol of the `reduce` method.
                const calleeObjType = (0, util_1.getConstrainedTypeAtLocation)(services, callee.object);
                // Check the owner type of the `reduce` method.
                if (isArrayType(calleeObjType)) {
                    context.report({
                        node: secondArg,
                        messageId: 'preferTypeParameter',
                        fix: fixer => {
                            const fixes = [
                                fixer.removeRange([
                                    secondArg.range[0],
                                    secondArg.expression.range[0],
                                ]),
                                fixer.removeRange([
                                    secondArg.expression.range[1],
                                    secondArg.range[1],
                                ]),
                            ];
                            if (!callee.parent.typeArguments) {
                                fixes.push(fixer.insertTextAfter(callee, `<${context.sourceCode.getText(secondArg.typeAnnotation)}>`));
                            }
                            return fixes;
                        },
                    });
                    return;
                }
            },
        };
    },
});