Fix a bug where the StringLiteralExpr convenience initializer would add to few #s to correctly contain a backslash

Author: ahoppen

Sources/SwiftSyntaxBuilder/ConvenienceInitializers/StringLiteralExprConvenienceInitializers.swift

@@ -19,7 +19,7 @@ private let rawStringPotentialEscapesPattern = try! NSRegularExpression(
   pattern: [
     #""(#*)"#, // Match potential opening delimiters
     #"(#*)""#, // Match potential closing delimiters
-    #"\\(#*)\("#, // Match potential interpolations
+    #"\\(#*)"#, // Match potential interpolations
   ].joined(separator: "|")
 )
 

Tests/SwiftSyntaxBuilderTest/StringLiteralTests.swift

@@ -34,4 +34,10 @@ final class StringLiteralTests: XCTestCase {
       AssertBuildResult(builder, expected, line: line)
     }
   }
+
+  func testEscapeBackslash() {
+    AssertBuildResult(StringLiteralExpr(content: #"\"#), ##"""
+    #"\"#
+    """##)
+  }
 }