Takes a string from the default implementation of `String(describing:)` and reformats it to be on multiple lines with indented properties. Useful when looking at logs or crash reports that generates strings from types using `String(describing:)`.

pretty-description.swift

#!/usr/bin/swift

import Darwin
import Foundation

var inputString = CommandLine.arguments.dropFirst().joined(separator: " ")
if inputString.isEmpty {
    while let line = readLine(strippingNewline: false) {
        inputString += line
    }
}

let scanner = Scanner(string: inputString)
scanner.charactersToBeSkipped = nil

let symbols = CharacterSet(charactersIn: "()<>[],")
var indentLevel = 0
var genericLevel = 0
var outputString = ""

func addNewline() {
    _ = scanner.scanCharacters(from: .whitespaces)
    outputString += "\n" + String(repeating: " ", count: indentLevel * 4)
}

while !scanner.isAtEnd {
    outputString += scanner.scanUpToCharacters(from: symbols) ?? ""
    
    guard let symbol = scanner.scanCharacter() else { continue }
    
    switch symbol {
    case "(", "[":
        indentLevel += 1
        outputString += String(symbol)
        addNewline()
    case ")", "]":
        indentLevel -= 1
        addNewline()
        outputString += String(symbol)
    case "<":
        genericLevel += 1
        outputString += String(symbol)
    case ">":
        genericLevel -= 1
        outputString += String(symbol)
    case ",":
        outputString += String(symbol)
        if genericLevel == 0 {
            addNewline()
        }
    default:
        break
    }
}

print(outputString)

Example

Input

User<G1<G2>, G3>(name: "Craig", address: __lldb_expr_43.Address(city: "Calgary", province: "AB"))

Output

User<G1<G2>, G3>(
    name: "Craig",
    address: __lldb_expr_39.Address(
        city: "Calgary",
        province: "AB"
    )
)