Update the project to Swift 5.4 (#125)

* Update the project to Swift 5.4

- Splash now uses the Swift 5.4 toolchain.
- Since Swift 5.4 now enables automatic test discovery on all supported
   platforms, all of the infrastructure that was previously used to maintain
   Linux unit testing compatibility has now been removed.

* Remove LinuxMain.swift

Author: JohnSundell

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.2
+// swift-tools-version:5.4
 
 /**
  *  Splash
@@ -19,19 +19,19 @@ let package = Package(
     ],
     targets: [
         .target(name: "Splash"),
-        .target(
+        .executableTarget(
             name: "SplashMarkdown",
             dependencies: ["Splash"]
         ),
-        .target(
+        .executableTarget(
             name: "SplashHTMLGen",
             dependencies: ["Splash"]
         ),
-        .target(
+        .executableTarget(
             name: "SplashImageGen",
             dependencies: ["Splash"]
         ),
-        .target(
+        .executableTarget(
             name: "SplashTokenizer",
             dependencies: ["Splash"]
         ),

Tests/LinuxMain.swift

@@ -10,7 +10,7 @@ import Splash
 
 /// Test case used as an abstract base class for all tests relating to
 /// syntax highlighting. For all such tests, the Swift grammar is used.
-class SyntaxHighlighterTestCase: SplashTestCase {
+class SyntaxHighlighterTestCase: XCTestCase {
     private(set) var highlighter: SyntaxHighlighter<OutputFormatMock>!
     private(set) var builder: OutputBuilderMock!
 

Tests/SplashTests/Core/SplashTestCase.swift

@@ -259,28 +259,4 @@ final class ClosureTests: SyntaxHighlighterTestCase {
             .plainText("}")
         ])
     }
-
-    func testAllTestsRunOnLinux() {
-        XCTAssertTrue(TestCaseVerifier.verifyLinuxTests((type(of: self)).allTests))
-    }
-}
-
-extension ClosureTests {
-    static var allTests: [(String, TestClosure<ClosureTests>)] {
-        return [
-            ("testTrailingClosureWithArguments", testTrailingClosureWithArguments),
-            ("testTrailingClosureWithoutParanthesis", testTrailingClosureWithoutParanthesis),
-            ("testEmptyTrailingClosure", testEmptyTrailingClosure),
-            ("testClosureArgumentWithSingleArgument", testClosureArgumentWithSingleArgument),
-            ("testClosureArgumentWithMultipleArguments", testClosureArgumentWithMultipleArguments),
-            ("testEscapingClosureArgument", testEscapingClosureArgument),
-            ("testClosureWithInoutArgument", testClosureWithInoutArgument),
-            ("testPassingClosureAsArgument", testPassingClosureAsArgument),
-            ("testNestedEscapingClosure", testNestedEscapingClosure),
-            ("testClosureArgumentShorthands", testClosureArgumentShorthands),
-            ("testClosureWithWeakSelfCaptureList", testClosureWithWeakSelfCaptureList),
-            ("testClosureWithUnownedSelfCaptureList", testClosureWithUnownedSelfCaptureList),
-            ("testClosureWithSingleFunctionCall", testClosureWithSingleFunctionCall)
-        ]
-    }
 }

Tests/SplashTests/Core/SyntaxHighlighterTestCase.swift

@@ -358,31 +358,4 @@ final class CommentTests: SyntaxHighlighterTestCase {
             .plainText("}")
         ])
     }
-
-    func testAllTestsRunOnLinux() {
-        XCTAssertTrue(TestCaseVerifier.verifyLinuxTests((type(of: self)).allTests))
-    }
-}
-
-extension CommentTests {
-    static var allTests: [(String, TestClosure<CommentTests>)] {
-        return [
-            ("testSingleLineComment", testSingleLineComment),
-            ("testMultiLineComment", testMultiLineComment),
-            ("testMultiLineCommentWithDoubleAsterisks", testMultiLineCommentWithDoubleAsterisks),
-            ("testMutliLineDocumentationComment", testMutliLineDocumentationComment),
-            ("testCommentStartingWithPunctuation", testCommentStartingWithPunctuation),
-            ("testCommentEndingWithComma", testCommentEndingWithComma),
-            ("testCommentPrecededByComma", testCommentPrecededByComma),
-            ("testCommentWithNumber", testCommentWithNumber),
-            ("testCommentWithNoWhiteSpaceToPunctuation", testCommentWithNoWhiteSpaceToPunctuation),
-            ("testCommentsNextToCurlyBrackets", testCommentsNextToCurlyBrackets),
-            ("testCommentWithinGenericTypeList", testCommentWithinGenericTypeList),
-            ("testCommentsNextToGenericTypeList", testCommentsNextToGenericTypeList),
-            ("testCommentsNextToInitialization", testCommentsNextToInitialization),
-            ("testCommentsNextToProtocolName", testCommentsNextToProtocolName),
-            ("testCommentsAfterOptionalTypes", testCommentsAfterOptionalTypes),
-            ("testCommentsAfterArrayTypes", testCommentsAfterArrayTypes)
-        ]
-    }
 }