Add support for Swift 5 single-line raw strings (#52)

This change makes Splash capable of highlighting Swift 5 raw strings,
although it’s currently limited to single line string literals. Support
for multi-line literals will be added in a future commit.

Sources/Splash/Grammar/SwiftGrammar.swift

@@ -22,6 +22,7 @@ public struct SwiftGrammar: Grammar {
         syntaxRules = [
             PreprocessingRule(),
             CommentRule(),
+            RawStringRule(),
             MultiLineStringRule(),
             SingleLineStringRule(),
             AttributeRule(),
@@ -98,6 +99,14 @@ private extension SwiftGrammar {
         }
     }
 
+    struct RawStringRule: SyntaxRule {
+        var tokenType: TokenType { return .string }
+
+        func matches(_ segment: Segment) -> Bool {
+            return segment.isWithinStringLiteral(withStart: "#\"", end: "\"#")
+        }
+    }
+
     struct MultiLineStringRule: SyntaxRule {
         var tokenType: TokenType { return .string }
 
@@ -114,7 +123,7 @@ private extension SwiftGrammar {
         var tokenType: TokenType { return .string }
 
         func matches(_ segment: Segment) -> Bool {
-            guard segment.isWithinStringLiteral else {
+            guard segment.isWithinStringLiteral(withStart: "\"", end: "\"") else {
                 return false
             }
 
@@ -377,14 +386,12 @@ private extension SwiftGrammar {
 }
 
 private extension Segment {
-    var isWithinStringLiteral: Bool {
-        let delimiter = "\""
-
-        if tokens.current.hasPrefix(delimiter) {
+    func isWithinStringLiteral(withStart start: String, end: String) -> Bool {
+        if tokens.current.hasPrefix(start) {
             return true
         }
 
-        if tokens.current.hasSuffix(delimiter) {
+        if tokens.current.hasSuffix(end) {
             return true
         }
 
@@ -397,18 +404,20 @@ private extension Segment {
                 continue
             }
 
-            if token == delimiter {
-                if markerCounts.start == markerCounts.end {
+            if token == start {
+                if start != end || markerCounts.start == markerCounts.end {
                     markerCounts.start += 1
                 } else {
                     markerCounts.end += 1
                 }
+            } else if token == end && start != end {
+                markerCounts.end += 1
             } else {
-                if token.hasPrefix(delimiter) {
+                if token.hasPrefix(start) {
                     markerCounts.start += 1
                 }
 
-                if token.hasSuffix(delimiter) {
+                if token.hasSuffix(end) {
                     markerCounts.end += 1
                 }
             }

Tests/SplashTests/Tests/LiteralTests.swift

@@ -100,6 +100,24 @@ final class LiteralTests: SyntaxHighlighterTestCase {
         ])
     }
 
+    func testSingleLineRawStringLiteral() {
+        let components = highlighter.highlight("""
+        #"A raw string \\(withoutInterpolation) yes"#
+        """)
+
+        XCTAssertEqual(components, [
+            .token("#\"A", .string),
+            .whitespace(" "),
+            .token("raw", .string),
+            .whitespace(" "),
+            .token("string", .string),
+            .whitespace(" "),
+            .token("\\(withoutInterpolation)", .string),
+            .whitespace(" "),
+            .token("yes\"#", .string)
+        ])
+    }
+
     func testDoubleLiteral() {
         let components = highlighter.highlight("let double = 1.13")
 
@@ -142,6 +160,7 @@ extension LiteralTests {
             ("testStringLiteralWithAttribute", testStringLiteralWithAttribute),
             ("testStringLiteralInterpolation", testStringLiteralInterpolation),
             ("testMultiLineStringLiteral", testMultiLineStringLiteral),
+            ("testSingleLineRawStringLiteral", testSingleLineRawStringLiteral),
             ("testDoubleLiteral", testDoubleLiteral),
             ("testIntegerLiteralWithSeparators", testIntegerLiteralWithSeparators)
         ]