Allow escaped quotes in tag parameters (#124)

* add escaping with "$"

* Add new constant

* Change escaping to double back slash

---------

Co-authored-by: Sam Bishop <sambobjr@gmail.com>

Sources/LeafKit/LeafLexer/LeafLexer.swift

@@ -160,7 +160,7 @@ internal struct LeafLexer {
             case .comma:
                 return .parameterDelimiter
             case .quote:
-                let read = src.readWhile { $0 != .quote && $0 != .newLine }
+                let read = readWithEscapingQuotes(src: &src)
                 guard src.peek() == .quote else {
                     throw LexerError(.unterminatedStringLiteral, src: src, lexed: lexed)
                 }
@@ -269,4 +269,14 @@ internal struct LeafLexer {
             return .parameter(.variable(name: name))
         }
     }
+
+    private func readWithEscapingQuotes(src: inout LeafRawTemplate) -> String {
+        let read = src.readWhile { $0 != .quote && $0 != .newLine }
+        if read.last == .backSlash && src.peek() == .quote {
+            src.pop()
+            return read.dropLast() + "\"" + readWithEscapingQuotes(src: &src)
+        } else {
+            return read
+        }
+    }
 }

Tests/LeafKitTests/LeafTests.swift

@@ -191,6 +191,16 @@ final class LeafTests: XCTestCase {
         try XCTAssertEqual(render(template, [:]), expected)
     }
 
+    func testEscapingQuote() throws {
+        let template = """
+        #("foo \\"bar\\"")
+        """
+        let expected = """
+        foo "bar"
+        """
+        try XCTAssertEqual(render(template), expected)
+    }
+
     func testCount() throws {
         let template = """
         count: #count(array)