Fix regex fixer to maintain string literal syntax (#78172)

* Fix regex fixer to maintain string literal syntax

* Simplify

* Still transform interpolated strings

2 files changed, 93 insertions, 1 deletions

diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index bf98ce298ec..442976d648b 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -274,6 +274,10 @@ namespace System.Text.RegularExpressions.Generator
                     string optionsLiteral = Literal(((RegexOptions)(int)argument.Value.ConstantValue.Value).ToString());
                     return SyntaxFactory.ParseExpression(optionsLiteral);
                 }
+                else if (argument.Value is ILiteralOperation literalOperation)
+                {
+                    return literalOperation.Syntax;
+                }
                 else
                 {
                     return generator.LiteralExpression(argument.Value.ConstantValue.Value);
diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
index 18c9e25b671..9dafdf41020 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
@@ -792,7 +792,7 @@ partial class Program
 static class Class
 {
     public static string CollapseWhitespace(this string text) =>
-        [|Regex.Replace(text, @"" \s+"" , ""  "")|];
+        [|Regex.Replace(text, "" \\s+"" , ""  "")|];
 }";
 
             string expectedFixedCode = @"using System.Text.RegularExpressions;
@@ -809,6 +809,94 @@ static partial class Class
         }
 
         [Fact]
+        public async Task VerbatimStringLiteralSyntaxPreservedByFixer()
+        {
+            string test = @"using System.Text.RegularExpressions;
+
+static class Class
+{
+    public static string CollapseWhitespace(this string text) =>
+        [|Regex.Replace(text, @"" \s+"" , @""  "")|];
+}";
+
+            string expectedFixedCode = @"using System.Text.RegularExpressions;
+
+static partial class Class
+{
+    public static string CollapseWhitespace(this string text) =>
+        MyRegex().Replace(text, @""  "");
+    [GeneratedRegex(@"" \s+"")]
+    private static partial Regex MyRegex();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
+        }
+
+        [Fact]
+        public async Task RawStringLiteralSyntaxPreservedByFixer()
+        {
+            string test = @"using System.Text.RegularExpressions;
+
+static class Class
+{
+    public static string CollapseWhitespace(this string text) =>
+        [|Regex.Replace(text, """"""
+                              \s+
+                              """""",
+                              """""""" hello """""" world """""""")|];
+}";
+
+            string expectedFixedCode = @"using System.Text.RegularExpressions;
+
+static partial class Class
+{
+    public static string CollapseWhitespace(this string text) =>
+        MyRegex().Replace(text, """""""" hello """""" world """""""");
+    [GeneratedRegex(""""""
+                              \s+
+                              """""")]
+    private static partial Regex MyRegex();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
+        }
+
+        [Fact]
+        public async Task InterpolatedStringLiteralSyntaxPreservedByFixer()
+        {
+            string test = @"using System.Text.RegularExpressions;
+
+partial class Program
+{
+    static void Main(string[] args)
+    {
+        const string pattern = @""a|b\s\n"";
+        const string pattern2 = $""{pattern}2"";
+
+        Regex regex = [|new Regex(pattern2)|];
+    }
+}";
+
+            string expectedFixedCode = @"using System.Text.RegularExpressions;
+
+partial class Program
+{
+    static void Main(string[] args)
+    {
+        const string pattern = @""a|b\s\n"";
+        const string pattern2 = $""{pattern}2"";
+
+        Regex regex = MyRegex();
+    }
+
+    [GeneratedRegex(""a|b\\s\\n2"")]
+    private static partial Regex MyRegex();
+}";
+
+            await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
+        }
+
+        [Fact]
         public async Task TestAsArgument()
         {
             string test = @"using System.Text.RegularExpressions;