`lineLength` with `multilineTrailingCommaBehavior : alwaysUsed` seems broken

[kkebo]

Input

.swift-format:

{
  "indentation" : {
    "spaces" : 4
  },
  "lineLength" : 120,
  "multilineTrailingCommaBehavior" : "alwaysUsed",
  "version" : 1
}

test.swift:

struct S {
    private mutating func doctype(_ input: inout BufferQueue) -> ProcessResult {
        repeat {
            switch self.getChar(from: &input) {
            case "\t", "\n", "\u{0C}", " ": #go(to: .beforeDOCTYPEName)
            case ">": #go(error: .missingDOCTYPEName, emitNewForceQuirksDOCTYPE: .data)
            case "\0":
                #go(error: .missingSpaceBeforeDOCTYPEName, .unexpectedNull, createDOCTYPE: "\u{FFFD}", to: .doctypeName)
            case nil:
                self.emitError(.eofInDOCTYPE)
                #goEmitNewForceQuirksDOCTYPEAndEOF
            case let c?: #go(error: .missingSpaceBeforeDOCTYPEName, createDOCTYPE: lowerASCII(c), to: .doctypeName)
            }
        } while true
    }
}

The line length of #go(error: .missingSpaceBeforeDOCTYPEName, .unexpectedNull, createDOCTYPE: "\u{FFFD}", to: .doctypeName) is just 120.

Expected result

No warnings.

Actual result

$ swift-format lint test.swift
test.swift:9:120: warning: [TrailingComma] add trailing comma to the last element in multiline collection literal
test.swift:8:1: warning: [LineLength] line is too long

If multilineTrailingCommaBehavior is keptAsWritten, there are no warnings.

Environment

• swift-format main branch 95ed8b4
• Linux aarch64

[kkebo]

The following example is a minimal failing test. (CommaTests)

  func testMultilineTrailingCommaBehaviorDoesNotAffectLineLength() {
    let input =
      """
      f(0, 0)

      """

    let expected = input

    var configuration = Configuration.forTesting
    configuration.multilineTrailingCommaBehavior = .alwaysUsed
    assertPrettyPrintEqual(input: input, expected: expected, linelength: 7, configuration: configuration)

    configuration.multilineTrailingCommaBehavior = .neverUsed
    assertPrettyPrintEqual(input: input, expected: expected, linelength: 7, configuration: configuration)

    configuration.multilineTrailingCommaBehavior = .keptAsWritten
    assertPrettyPrintEqual(input: input, expected: expected, linelength: 7, configuration: configuration)
  }

[kkebo]

The following logic is the cause.

swift-format/Sources/SwiftFormat/PrettyPrint/PrettyPrint.swift

Lines 704 to 716 in 7ddf4e1

	case .commaDelimitedRegionEnd(let isCollection, _, let isSingleElement):
	// The token's length is only necessary when a comma will be printed, but it's impossible to
	// know at this point whether the region-start token will be on the same line as this token.
	// Without adding this length to the total, it would be possible for this comma to be
	// printed in column `maxLineLength`. Unfortunately, this can cause breaks to fire
	// unnecessarily when the enclosed tokens comma would fit within `maxLineLength`.
	if shouldHandleCommaDelimitedRegion(isCollection: isCollection) == true {
	let length = isSingleElement ? 0 : 1
	total += length
	lengths.append(length)
	} else {
	lengths.append(0)
	}