SwiftLint/Source/SwiftLintBuiltInRules/Rules/Idiomatic/XCTFailMessageRule.swift

import SwiftSyntax

@SwiftSyntaxRule
struct XCTFailMessageRule: Rule {
    var configuration = SeverityConfiguration<Self>(.warning)

    static let description = RuleDescription(
        identifier: "xctfail_message",
        name: "XCTFail Message",
        description: "An XCTFail call should include a description of the assertion",
        kind: .idiomatic,
        nonTriggeringExamples: [
            Example("""
            func testFoo() {
              XCTFail("bar")
            }
            """),
            Example("""
            func testFoo() {
              XCTFail(bar)
            }
            """)
        ],
        triggeringExamples: [
            Example("""
            func testFoo() {
              ↓XCTFail()
            }
            """),
            Example("""
            func testFoo() {
              ↓XCTFail("")
            }
            """)
        ]
    )
}

private extension XCTFailMessageRule {
    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
        override func visitPost(_ node: FunctionCallExprSyntax) {
            guard
                let expression = node.calledExpression.as(DeclReferenceExprSyntax.self),
                expression.baseName.text == "XCTFail",
                node.arguments.isEmptyOrEmptyString
            else {
                return
            }

            violations.append(node.positionAfterSkippingLeadingTrivia)
        }
    }
}

private extension LabeledExprListSyntax {
    var isEmptyOrEmptyString: Bool {
        if isEmpty {
            return true
        }
        return count == 1 && first?.expression.as(StringLiteralExprSyntax.self)?.isEmptyString == true
    }
}