Crash: WhitespaceLinter.contiguousWhitespace(startingAt:in:)

[lukbukkit]

When applying swift-format to my project it crashes with following stack trace:

💣 Program crashed: System trap at 0x0000aaaac5d215e0

Thread 0 "swift-format" crashed:

 0 WhitespaceLinter.contiguousWhitespace(startingAt:in:) in swift-format at /home/build-user/swift-format/Sources/SwiftFormat/PrettyPrint/WhitespaceLinter.swift:327:11
 1 WhitespaceLinter.lint() + 660 in swift-format at /home/build-user/swift-format/Sources/SwiftFormat/PrettyPrint/WhitespaceLinter.swift:56:33
 2 SwiftLinter.lint(syntax:operatorTable:assumingFileURL:source:) + 715 in swift-format at /home/build-user/swift-format/Sources/SwiftFormat/API/SwiftLinter.swift:155:8
 3 SwiftLinter.lint(source:assumingFileURL:parsingDiagnosticHandler:) + 307 in swift-format at /home/build-user/swift-format/Sources/SwiftFormat/API/SwiftLinter.swift:101:9
 4 LintFrontend.processFile(_:) + 555 in swift-format at /home/build-user/swift-format/Sources/swift-format/Frontend/LintFrontend.swift:33:18
 5 specialized Sequence.forEach(_:) + 2491 in swift-format at /home/build-user/swift-format/Sources/swift-format/Frontend/Frontend.swift:153:18
 6 implicit closure #7 in Frontend.processURLs(_:parallel:) in swift-format at /home/build-user/swift-format/Sources/swift-format/Frontend/Frontend.swift:153:10
 7 Frontend.processURLs(_:parallel:) + 699 in swift-format at /home/build-user/swift-format/Sources/swift-format/Frontend/Frontend.swift:153:18
 8 Frontend.run() + 199 in swift-format at /home/build-user/swift-format/Sources/swift-format/Frontend/Frontend.swift:102:7
 9 closure #1 in SwiftFormatCommand.Lint.run() + 123 in swift-format at /home/build-user/swift-format/Sources/swift-format/Subcommands/Lint.swift:37:18
10 specialized PerformanceMeasurementsOptions.printingInstructionCountIfRequested<A>(_:) in swift-format at Sources/swift-format/Subcommands/PerformanceMeasurement.swift:24:18
11 SwiftFormatCommand.Lint.run() + 175 in swift-format at /home/build-user/swift-format/Sources/swift-format/Subcommands/Lint.swift:35:41
12 0x0000ffff938f84c4 <unknown> in libc.so.6
13 0x0000ffff938f8598 <unknown> in libc.so.6

Here's how you can reproduce the crash:

# Clone the repository
git clone https://github.com/seemoo-lab/CellGuard.git
# Run swift-format included with the latest swift Docker container
docker run --rm -it -v $(pwd)/CellGuard:/app:ro swift:latest
# Inside the container go to the mounted directory
cd /app/CellGuardAppSwift
# Run swift-format
swift format lint -r .
# At some point, you'll encounter this crash

Best
Lukas

[TTOzzi]

Hello @lukbukkit!
Thank you for reporting this issue along with the reproduction steps.

I took a quick look into the cause, and it seems that the crash occurs due to a special unicode line separator character(U+2028) present in UserStudyView.swift.

You can check for this character by copying it from here and using Command + F to search for it.
As a temporary workaround, you can simply remove this character to resolve the issue immediately.

[lukbukkit]

Thanks for your quick reply and the workaround! It fixes the crash. I assume those Unicode characters originate from a PDF from which we copied the text.