SwiftLint/Source/SwiftLintBuiltInRules/Rules/Style/ImplicitGetterRule.swift

import SwiftSyntax

struct ImplicitGetterRule: ConfigurationProviderRule, SwiftSyntaxRule {
    var configuration = SeverityConfiguration<Self>(.warning)

    static let description = RuleDescription(
        identifier: "implicit_getter",
        name: "Implicit Getter",
        description: "Computed read-only properties and subscripts should avoid using the get keyword.",
        kind: .style,
        nonTriggeringExamples: ImplicitGetterRuleExamples.nonTriggeringExamples,
        triggeringExamples: ImplicitGetterRuleExamples.triggeringExamples
    )

    func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
        ImplicitGetterRuleVisitor(viewMode: .sourceAccurate)
    }
}

private final class ImplicitGetterRuleVisitor: ViolationsSyntaxVisitor {
    enum ViolationKind {
        case `subscript`, property

        var violationDescription: String {
            switch self {
            case .subscript:
                return "Computed read-only subscripts should avoid using the get keyword"
            case .property:
                return "Computed read-only properties should avoid using the get keyword"
            }
        }
    }

    override func visitPost(_ node: AccessorBlockSyntax) {
        guard let getAccessor = node.getAccessor,
              node.setAccessor == nil,
              getAccessor.effectSpecifiers == nil,
              getAccessor.modifier == nil,
              (getAccessor.attributes == nil || getAccessor.attributes?.isEmpty == true),
              getAccessor.body != nil else {
            return
        }

        let kind: ViolationKind = node.parent?.as(SubscriptDeclSyntax.self) == nil ? .property : .subscript
        violations.append(
            ReasonedRuleViolation(
                position: getAccessor.positionAfterSkippingLeadingTrivia,
                reason: kind.violationDescription
            )
        )
    }
}