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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import SwiftSyntax
/// Numeric literals should be grouped with `_`s to delimit common separators.
///
/// Specifically, decimal numeric literals should be grouped every 3 numbers, hexadecimal every 4,
/// and binary every 8.
///
/// Lint: If a numeric literal is too long and should be grouped, a lint error is raised.
///
/// Format: All numeric literals that should be grouped will have `_`s inserted where appropriate.
///
/// TODO: Minimum numeric literal length bounds and numeric groupings have been selected arbitrarily;
/// these could be reevaluated.
/// TODO: Handle floating point literals.
@_spi(Rules)
public final class GroupNumericLiterals: SyntaxFormatRule {
public override func visit(_ node: IntegerLiteralExprSyntax) -> ExprSyntax {
var originalDigits = node.literal.text
guard !originalDigits.contains("_") else { return ExprSyntax(node) }
let isNegative = originalDigits.first == "-"
originalDigits = isNegative ? String(originalDigits.dropFirst()) : originalDigits
var newDigits = ""
switch originalDigits.prefix(2) {
case "0x":
// Hexadecimal
let digitsNoPrefix = String(originalDigits.dropFirst(2))
guard digitsNoPrefix.count >= 8 else { return ExprSyntax(node) }
diagnose(.groupNumericLiteral(every: 4, base: "hexadecimal"), on: node)
newDigits = "0x" + digits(digitsNoPrefix, groupedEvery: 4)
case "0b":
// Binary
let digitsNoPrefix = String(originalDigits.dropFirst(2))
guard digitsNoPrefix.count >= 10 else { return ExprSyntax(node) }
diagnose(.groupNumericLiteral(every: 8, base: "binary"), on: node)
newDigits = "0b" + digits(digitsNoPrefix, groupedEvery: 8)
case "0o":
// Octal
return ExprSyntax(node)
default:
// Decimal
guard originalDigits.count >= 7 else { return ExprSyntax(node) }
diagnose(.groupNumericLiteral(every: 3, base: "decimal"), on: node)
newDigits = digits(originalDigits, groupedEvery: 3)
}
newDigits = isNegative ? "-" + newDigits : newDigits
var result = node
result.literal.tokenKind = .integerLiteral(newDigits)
return ExprSyntax(result)
}
/// Returns a copy of the given string with an underscore (`_`) inserted between every group of
/// `stride` digits, counting from the right.
///
/// Precondition: `digits` does not already contain underscores.
private func digits(_ digits: String, groupedEvery stride: Int) -> String {
var newGrouping = Array(digits)
var i = 1
while i * stride < digits.count {
newGrouping.insert("_", at: digits.count - i * stride)
i += 1
}
return String(newGrouping)
}
}
extension Finding.Message {
fileprivate static func groupNumericLiteral(every stride: Int, base: String) -> Finding.Message {
return "group every \(stride) digits in this \(base) literal using a '_' separator"
}
}
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