SwiftFormat/Sources/Rules/ElseOnSameLine.swift

//
//  ElseOnSameLine.swift
//  SwiftFormat
//
//  Created by Nick Lockwood on 8/22/16.
//  Copyright © 2024 Nick Lockwood. All rights reserved.
//

import Foundation

public extension FormatRule {
    /// Ensure that an `else` statement following `if { ... }` appears on the same line
    /// as the closing brace. This has no effect on the `else` part of a `guard` statement.
    /// Also applies to `catch` after `try` and `while` after `repeat`.
    static let elseOnSameLine = FormatRule(
        help: """
        Place `else`, `catch` or `while` keyword in accordance with current style (same or
        next line).
        """,
        orderAfter: [.wrapMultilineStatementBraces],
        options: ["else-position", "guard-else"],
        sharedOptions: ["allman", "linebreaks"]
    ) { formatter in
        formatter.forEachToken { i, token in
            switch token {
            case .keyword("while"):
                if let endIndex = formatter.index(of: .nonSpaceOrCommentOrLinebreak, before: i, if: {
                    $0 == .endOfScope("}")
                }), let startIndex = formatter.index(of: .startOfScope("{"), before: endIndex),
                formatter.last(.nonSpaceOrCommentOrLinebreak, before: startIndex) == .keyword("repeat") {
                    fallthrough
                }
            case .keyword("else"):
                guard var prevIndex = formatter.index(of: .nonSpace, before: i),
                      let nextIndex = formatter.index(of: .nonSpaceOrLinebreak, after: i, if: {
                          !$0.isComment
                      })
                else {
                    return
                }
                let isOnNewLine = formatter.tokens[prevIndex].isLinebreak
                if isOnNewLine {
                    prevIndex = formatter.index(of: .nonSpaceOrLinebreak, before: i) ?? prevIndex
                }
                if formatter.tokens[prevIndex] == .endOfScope("}"), !formatter.isGuardElse(at: i) {
                    fallthrough
                }
                guard let guardIndex = formatter.indexOfLastSignificantKeyword(at: prevIndex + 1, excluding: [
                    "var", "let", "case",
                ]), formatter.tokens[guardIndex] == .keyword("guard") else {
                    return
                }
                let shouldWrap: Bool
                switch formatter.options.guardElsePosition {
                case .auto:
                    // Only wrap if else or following brace is on next line
                    shouldWrap = isOnNewLine ||
                        formatter.tokens[i + 1 ..< nextIndex].contains { $0.isLinebreak }
                case .nextLine:
                    // Only wrap if guard statement spans multiple lines
                    shouldWrap = isOnNewLine ||
                        formatter.tokens[guardIndex + 1 ..< nextIndex].contains { $0.isLinebreak }
                case .sameLine:
                    shouldWrap = false
                }
                if shouldWrap {
                    if !formatter.options.allmanBraces {
                        formatter.replaceTokens(in: i + 1 ..< nextIndex, with: .space(" "))
                    }
                    if !isOnNewLine {
                        formatter.replaceTokens(in: prevIndex + 1 ..< i, with:
                            formatter.linebreakToken(for: prevIndex + 1))
                        formatter.insertSpace(formatter.currentIndentForLine(at: guardIndex), at: prevIndex + 2)
                    }
                } else if isOnNewLine {
                    formatter.replaceTokens(in: prevIndex + 1 ..< i, with: .space(" "))
                }
            case .keyword("catch"):
                guard let prevIndex = formatter.index(of: .nonSpace, before: i) else {
                    return
                }

                let precededByBlankLine = formatter.tokens[prevIndex].isLinebreak
                    && formatter.lastToken(before: prevIndex, where: { !$0.isSpaceOrComment })?.isLinebreak == true

                if precededByBlankLine {
                    return
                }

                let shouldWrap = formatter.options.allmanBraces || formatter.options.elsePosition == .nextLine
                if !shouldWrap, formatter.tokens[prevIndex].isLinebreak {
                    if let prevBraceIndex = formatter.index(of: .nonSpaceOrLinebreak, before: prevIndex, if: {
                        $0 == .endOfScope("}")
                    }), formatter.bracesContainLinebreak(prevBraceIndex) {
                        formatter.replaceTokens(in: prevBraceIndex + 1 ..< i, with: .space(" "))
                    }
                } else if shouldWrap, let token = formatter.token(at: prevIndex), !token.isLinebreak,
                          let prevBraceIndex = (token == .endOfScope("}")) ? prevIndex :
                          formatter.index(of: .nonSpaceOrCommentOrLinebreak, before: prevIndex, if: {
                              $0 == .endOfScope("}")
                          }), formatter.bracesContainLinebreak(prevBraceIndex)
                {
                    formatter.replaceTokens(in: prevIndex + 1 ..< i, with:
                        formatter.linebreakToken(for: prevIndex + 1))
                    formatter.insertSpace(formatter.currentIndentForLine(at: prevIndex + 1), at: prevIndex + 2)
                }
            default:
                break
            }
        }
    } examples: {
        """
        ```diff
          if x {
            // foo
        - }
        - else {
            // bar
          }

          if x {
            // foo
        + } else {
            // bar
          }
        ```

        ```diff
          do {
            // try foo
        - }
        - catch {
            // bar
          }

          do {
            // try foo
        + } catch {
            // bar
          }
        ```

        ```diff
          repeat {
            // foo
        - }
        - while {
            // bar
          }

          repeat {
            // foo
        + } while {
            // bar
          }
        ```
        """
    }
}

extension Formatter {
    func bracesContainLinebreak(_ endIndex: Int) -> Bool {
        guard let startIndex = index(of: .startOfScope("{"), before: endIndex) else {
            return false
        }
        return (startIndex ..< endIndex).contains(where: { tokens[$0].isLinebreak })
    }
}