Dont fail when there is no file

[MadsBogeskov]

In my process into moving to Danger Swift from Danger JS I got this error:

Fatal error: Unexpectedly found nil while unwrapping an Optional value: file Danger/SwiftLintViolation.swift, line 23
Stack dump:
0.	Program arguments: /Applications/Xcode_12.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -interpret /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/_tmp_dangerfile.swift -enable-objc-interop -stack-check -sdk /Applications/Xcode_12.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -I /Users/runner/work/ios-app/ios-app/.build/debug -target-sdk-version 10.15.6 -module-name _tmp_dangerfile -lDanger -- runner /usr/local/lib/node_modules/danger/distribution/commands/danger-ci.js --process .build/debug/danger-swift --passURLForDSL /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/danger-dsl.json /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/danger-response.json 
1.	Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1)
2.	While running user code "/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/_tmp_dangerfile.swift"
0  swift                    0x0000000112e57865 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift                    0x0000000112e56865 llvm::sys::RunSignalHandlers() + 85
2  swift                    0x0000000112e57e1f SignalHandler(int) + 111
3  libsystem_platform.dylib 0x00007fff7210e5fd _sigtramp + 29
4  libsystem_notify.dylib   0x00007fff721046da notify_register_plain + 711
5  libswiftCore.dylib       0x00007fff7156dcf7 $ss17_assertionFailure__4file4line5flagss5NeverOs12StaticStringV_A2HSus6UInt32VtFySRys5UInt8VGXEfU_yAMXEfU_ + 87
6  libswiftCore.dylib       0x00007fff7156d9c3 $ss17_assertionFailure__4file4line5flagss5NeverOs12StaticStringV_A2HSus6UInt32VtFySRys5UInt8VGXEfU_ + 99
7  libswiftCore.dylib       0x00007fff7156d5d5 $ss17_assertionFailure__4file4line5flagss5NeverOs12StaticStringV_A2HSus6UInt32VtF + 533
8  libDanger.dylib          0x0000000118287ed7 $s6Danger18SwiftLintViolationV10toMarkdownSSyF + 743
9  libDanger.dylib          0x0000000118285a4b $s6Danger9SwiftLintV4lint6danger13shellExecutor13swiftlintPath6inline9directory10configFile6strict0D8AllFiles07currentI8Provider06outputmI013reportDeleter14markdownAction04failW00x6InlineW004warnyW004readM0SayAA0bC9ViolationVGAA0A3DSLV_0a5ShellG014ShellExecuting_pSSSbSSSgA0_S2bAA07CurrentiR0_pSSAA23SwiftlintReportDeleting_pySSXEySSXEySS_SSSitXEySS_SSSitXES2SXEtFZSSAVXEfU1_ + 27
10 libDanger.dylib          0x0000000118285ab6 $s6Danger18SwiftLintViolationVSSs5Error_pIggozo_ACSSsAD_pIegnrzo_TR + 86
11 libDanger.dylib          0x0000000118286024 $s6Danger18SwiftLintViolationVSSs5Error_pIggozo_ACSSsAD_pIegnrzo_TRTA + 20
12 libswiftCore.dylib       0x00007fff7154d505 $sSlsE3mapySayqd__Gqd__7ElementQzKXEKlF + 757
13 libDanger.dylib          0x00000001182834f2 $s6Danger9SwiftLintV4lint6danger13shellExecutor13swiftlintPath6inline9directory10configFile6strict0D8AllFiles07currentI8Provider06outputmI013reportDeleter14markdownAction04failW00x6InlineW004warnyW004readM0SayAA0bC9ViolationVGAA0A3DSLV_0a5ShellG014ShellExecuting_pSSSbSSSgA0_S2bAA07CurrentiR0_pSSAA23SwiftlintReportDeleting_pySSXEySSXEySS_SSSitXEySS_SSSitXES2SXEtFZ + 3218
14 libDanger.dylib          0x0000000118282086 $s6Danger9SwiftLintV4lint6inline9directory10configFile6strict0D8AllFiles13swiftlintPathSayAA0bC9ViolationVGSb_SSSgANS2bANtFZ + 1078
15 libDanger.dylib          0x00000001184c809d $s6Danger9SwiftLintV4lint6inline9directory10configFile6strict0D8AllFiles13swiftlintPathSayAA0bC9ViolationVGSb_SSSgANS2bANtFZ + 2384973
16 swift                    0x000000010ea165cf llvm::orc::runAsMain(int (*)(int, char**), llvm::ArrayRef<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, llvm::Optional<llvm::StringRef>) + 2495
17 swift                    0x000000010e9f39cb swift::RunImmediately(swift::CompilerInstance&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, swift::IRGenOptions const&, swift::SILOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >&&) + 6747
18 swift                    0x000000010e9ceafa performCompileStepsPostSILGen(swift::CompilerInstance&, swift::CompilerInvocation const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, swift::PrimarySpecificPaths const&, int&, swift::FrontendObserver*) + 2426
19 swift                    0x000000010e9beae0 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 21152
20 swift                    0x000000010e93fc07 main + 1255
21 libdyld.dylib            0x00007fff71f11cc9 start + 1
22 libdyld.dylib            0x0000000000000017 start + 18446603338604536655
�[31mERROR: Dangerfile eval failed at Dangerfile.swift
�[0;0m�[31mERROR: Could not get the results JSON file at /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/danger-response.json
�[0;0m

The Dangerfile is pretty basic:

import Danger 
let danger = Danger()

SwiftLint.lint()

When I ran SwiftLint locally I got this output:

  {
    "character" : null,
    "file" : "\/Users\/REDACTED\/Developer\/path\/ios-app\/Danger\/App.swift",
    "line" : 6,
    "reason" : "Files should have a single trailing newline.",
    "rule_id" : "trailing_newline",
    "severity" : "Warning",
    "type" : "Trailing Newline"
  },
  {
    "character" : 0,
    "file" : "",
    "line" : 0,
    "reason" : "Number of warnings exceeded threshold of 1.",
    "rule_id" : "warning_threshold",
    "severity" : "Error",
    "type" : "Warning Threshold"
  }

So the problem seems to be that the last block failed since Danger was force unwrapping the file field:

public func toMarkdown() -> String {
        let formattedFile = file.split(separator: "/").last! + ":\(line)"

This PR just fixes this issue by removing the force unwrap, however perhaps there should be a special case handling for errors of type: warning_threshold also.

[417-72KI]

Suggested change

	let formattedFile = filename + ":\(line)"
	let formattedFile = "\(filename):\(line)"

IMO, unifying to interpolation or concatenation is better than mixed.

[f-meloni]

Makes sense to me, thank you for the PR :)

I agree with @417-72KI that would be better to not mix interpolation and concatenation, but I see it as minor so approving anyway.

[f-meloni]

I was thinking that we could use an empty string instead, given is not relevant for that error.

Suggested change

	let filename = file.split(separator: "/").last ?? "unknown"
	let formattedFile = filename + ":\(line)"
	let formattedFile = file.split(separator: "/").last.map { "\($0):\(line)" } ?? ""