From a8c393d599f89645e2ea7b57445cdc7a5638f8f4 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sat, 11 Oct 2025 16:10:00 +0000
Subject: [PATCH 1/6] Initial plan


From 25c081736865551796065985966d426e22aa5156 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sat, 11 Oct 2025 16:37:44 +0000
Subject: [PATCH 2/6] Fix multiline pattern preservation in GeneratedRegex
 fixer

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
---
 .../gen/UpgradeToGeneratedRegexCodeFixer.cs   | 11 +++-
 .../UpgradeToGeneratedRegexAnalyzerTests.cs   | 64 +++++++++++++++++++
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index aa3629a882310e..4267d0bc4070a7 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -295,9 +295,9 @@ static RegexOptions GetRegexOptionsFromArgument(ImmutableArray<IArgumentOperatio
                         return SyntaxFactory.ParseExpression(optionsLiteral);
 
                     case UpgradeToGeneratedRegexAnalyzer.PatternArgumentName:
-                        if (argument.Value.ConstantValue.Value is string str && str.Contains('\\'))
+                        if (argument.Value.ConstantValue.Value is string str && ShouldUseVerbatimString(str))
                         {
-                            // Special handling for string patterns with escaped characters
+                            // Special handling for string patterns with escaped characters or newlines
                             string escapedVerbatimText = str.Replace("\"", "\"\"");
                             return SyntaxFactory.ParseExpression($"@\"{escapedVerbatimText}\"");
                         }
@@ -313,6 +313,13 @@ static RegexOptions GetRegexOptionsFromArgument(ImmutableArray<IArgumentOperatio
                 }
             }
 
+            static bool ShouldUseVerbatimString(string str)
+            {
+                // Use verbatim string syntax if the string contains backslashes or newlines
+                // to preserve readability, especially for patterns with RegexOptions.IgnorePatternWhitespace
+                return str.Contains('\\') || str.Contains('\n') || str.Contains('\r');
+            }
+
             static string Literal(string stringifiedRegexOptions)
             {
                 if (int.TryParse(stringifiedRegexOptions, NumberStyles.Integer, CultureInfo.InvariantCulture, out int options))
diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
index c019531af8f9cf..b3c5e4ea3d9a30 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
@@ -1336,6 +1336,70 @@ static void Main(string[] args)
             await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
         }
 
+        [Fact]
+        public async Task MultilineVerbatimStringPreservedByFixer()
+        {
+            string test = """
+                using System.Text.RegularExpressions;
+
+                static class Class
+                {
+                    private static Regex r = [|new Regex(@"a
+                             b
+                             c", RegexOptions.IgnorePatternWhitespace)|];
+                }
+                """;
+
+            string expectedFixedCode = """
+                using System.Text.RegularExpressions;
+
+                static partial class Class
+                {
+                    private static Regex r = MyRegex();
+
+                    [GeneratedRegex(@"a
+                             b
+                             c", RegexOptions.IgnorePatternWhitespace)]
+                    private static partial Regex MyRegex();
+                }
+                """;
+
+            await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
+        }
+
+        [Fact]
+        public async Task MultilineStringConcatenationPreservedByFixer()
+        {
+            string test = """
+                using System.Text.RegularExpressions;
+
+                static class Class
+                {
+                    private const string foo = "bar";
+                    private static Regex r1 = [|new Regex(@"a        " + foo + @"
+                                                        b
+                                                        c", RegexOptions.IgnorePatternWhitespace)|];
+                }
+                """;
+
+            string expectedFixedCode = """
+                using System.Text.RegularExpressions;
+
+                static partial class Class
+                {
+                    private const string foo = "bar";
+                    private static Regex r1 = MyRegex();
+
+                    [GeneratedRegex(@"a        bar
+                                                        b
+                                                        c", RegexOptions.IgnorePatternWhitespace)]
+                    private static partial Regex MyRegex();
+                }
+                """;
+
+            await VerifyCS.VerifyCodeFixAsync(test, expectedFixedCode);
+        }
+
         [Fact]
         public async Task TestAsArgument()
         {

From 84e80b850aec82588fc5123da72086f834227605 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sat, 11 Oct 2025 23:11:28 +0000
Subject: [PATCH 3/6] Use IndexOfAny instead of multiple Contains calls

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
---
 .../gen/UpgradeToGeneratedRegexCodeFixer.cs                     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index 4267d0bc4070a7..692ca205144df3 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -317,7 +317,7 @@ static bool ShouldUseVerbatimString(string str)
             {
                 // Use verbatim string syntax if the string contains backslashes or newlines
                 // to preserve readability, especially for patterns with RegexOptions.IgnorePatternWhitespace
-                return str.Contains('\\') || str.Contains('\n') || str.Contains('\r');
+                return str.IndexOfAny(['\\', '\n', '\r']) >= 0;
             }
 
             static string Literal(string stringifiedRegexOptions)

From 1f0a9b5c9666d92e26b6c05c897dbd90546ffcec Mon Sep 17 00:00:00 2001
From: Tarek Mahmoud Sayed <10833894+tarekgh@users.noreply.github.com>
Date: Fri, 17 Oct 2025 11:34:34 -0700
Subject: [PATCH 4/6] restore the method specifier

---
 .../gen/UpgradeToGeneratedRegexCodeFixer.cs                     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index 133368cec256ad..c62ddded663815 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -401,7 +401,7 @@ private static RegexOptions GetRegexOptionsFromArgument(ImmutableArray<IArgument
             return null;
         }
 
-        static bool ShouldUseVerbatimString(string str)
+        private static bool ShouldUseVerbatimString(string str)
         {
             // Use verbatim string syntax if the string contains backslashes or newlines
             // to preserve readability, especially for patterns with RegexOptions.IgnorePatternWhitespace

From 8dc773c12db3bfdfd14fcc5bcdc499715d2540e8 Mon Sep 17 00:00:00 2001
From: Tarek Mahmoud Sayed <10833894+tarekgh@users.noreply.github.com>
Date: Fri, 17 Oct 2025 11:38:04 -0700
Subject: [PATCH 5/6] Restore method specifier

---
 .../gen/UpgradeToGeneratedRegexCodeFixer.cs                     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
index c62ddded663815..3075ea0811f5e5 100644
--- a/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
+++ b/src/libraries/System.Text.RegularExpressions/gen/UpgradeToGeneratedRegexCodeFixer.cs
@@ -408,7 +408,7 @@ private static bool ShouldUseVerbatimString(string str)
             return str.IndexOfAny(['\\', '\n', '\r']) >= 0;
         }
 
-        static string Literal(string stringifiedRegexOptions)
+        private static string Literal(string stringifiedRegexOptions)
         {
             if (int.TryParse(stringifiedRegexOptions, NumberStyles.Integer, CultureInfo.InvariantCulture, out int options))
             {

From cd60f06832f284d35f80c6a498640919942b6491 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 23 Oct 2025 18:22:35 +0000
Subject: [PATCH 6/6] Fix tests to use property syntax instead of method syntax

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
---
 .../UpgradeToGeneratedRegexAnalyzerTests.cs                | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
index 91ebb77f9bc518..ac63829ade7d13 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
@@ -1358,12 +1358,10 @@ static class Class
 
                 static partial class Class
                 {
-                    private static Regex r = MyRegex();
-
                     [GeneratedRegex(@"a
                              b
                              c", RegexOptions.IgnorePatternWhitespace)]
-                    private static partial Regex MyRegex();
+                    private static partial Regex r { get; }
                 }
                 """;
 
@@ -1391,12 +1389,11 @@ static class Class
                 static partial class Class
                 {
                     private const string foo = "bar";
-                    private static Regex r1 = MyRegex();
 
                     [GeneratedRegex(@"a        bar
                                                         b
                                                         c", RegexOptions.IgnorePatternWhitespace)]
-                    private static partial Regex MyRegex();
+                    private static partial Regex r1 { get; }
                 }
                 """;