Rule Request: Legacy Multiple

[marcelofabri]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

New rule request

Prefer using x.isMultiple(of: y) than x % y == 0.

1. Why should this rule be added? Share links to existing discussion about what
   the community thinks about this.

https://github.com/apple/swift-evolution/blob/master/proposals/0225-binaryinteger-iseven-isodd-ismultiple.md

2. Provide several examples of what would and wouldn't trigger violations.

Would trigger

// UITableView alternating row colour
cell.contentView.backgroundColor = indexPath.row % 2 == 0 ? .gray : .white

// Codable.swift.gyb in apple/swift
guard count % 2 == 0 else { throw DecodingError.dataCorrupted(...) }

// Bool.swift in apple/swift
public static func random<T: RandomNumberGenerator>(using generator: inout T) -> Bool {
    return (generator.next() >> 17) & 1 == 0
}

// KeyPath.swift in apple/swift
_sanityCheck(bytes > 0 && bytes % 4 == 0, "capacity must be multiple of 4 bytes")

// ReversedCollection Index.base documentation https://developer.apple.com/documentation/swift/reversedcollection/index/2965437-base
guard let i = reversedNumbers.firstIndex(where: { $0 % 2 == 0 })

Wouldn't trigger

// UITableView alternating row colour
cell.contentView.backgroundColor = indexPath.row.isMultiple(of: 2) ? .gray : .white

// Codable.swift.gyb in apple/swift
guard count.isMultiple(of: 2) else { throw DecodingError.dataCorrupted(...) }

// Bool.swift in apple/swift
public static func random<T: RandomNumberGenerator>(using generator: inout T) -> Bool {
    return (generator.next() >> 17).isMultiple(of: 2)
}

// KeyPath.swift in apple/swift
_sanityCheck(bytes > 0 && bytes.isMultiple(of: 4), "capacity must be multiple of 4 bytes")

// not used in a boolean context
let secretValue = (value % 3) + 2

3. Should the rule be configurable, if so what parameters should be configurable?

Just severity

4. Should the rule be opt-in or enabled by default? Why?
   See README.md for guidelines on when to mark a rule as opt-in.

Opt-in as isMultiple(of:) is only available on Swift 5+.