Use invariant culture when formatting transfer capture in regex source generator (#113081)

stephentoub · web-flow · commit f0aa3abca0e5 · 2025-03-04T10:56:18.000-05:00
A balancing group can result in TransferCapture being emitted with a negative "capnum". If the compiler is running under a culture that uses something other than '-' as the negative sign, the resulting generated code will fail to compile.
diff --git a/src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs b/src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs
@@ -2573,7 +2573,7 @@ void EmitCapture(RegexNode node, RegexNode? subsequent = null)
                     }
 
                     writer.WriteLine();
-                    writer.WriteLine($"base.TransferCapture({capnum}, {uncapnum}, {startingPos}, pos);");
+                    writer.WriteLine($"base.TransferCapture({capnum.ToString(CultureInfo.InvariantCulture)}, {uncapnum}, {startingPos}, pos);");
                 }
 
                 if (isAtomic || !childBacktracks)
diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorHelper.netcoreapp.cs
@@ -134,6 +134,12 @@ internal static async Task<Regex> SourceGenRegexAsync(
             return results[0];
         }
 
+        private static readonly CultureInfo s_cultureWithMinusNegativeSign = new CultureInfo("")
+        {
+            // To validate that generation still succeeds even when something other than '-' is used.
+            NumberFormat = new NumberFormatInfo() { NegativeSign = $"{(char)0x2212}" }
+        };
+
         internal static async Task<Regex[]> SourceGenRegexAsync(
             (string pattern, CultureInfo? culture, RegexOptions? options, TimeSpan? matchTimeout)[] regexes, CancellationToken cancellationToken = default)
         {
@@ -214,13 +220,24 @@ internal static async Task<Regex[]> SourceGenRegexAsync(
             comp = comp.ReplaceSyntaxTree(comp.SyntaxTrees.First(), CSharpSyntaxTree.ParseText(SourceText.From(code.ToString(), Encoding.UTF8), s_previewParseOptions));
 
             // Run the generator
-            GeneratorDriverRunResult generatorResults = s_generatorDriver.RunGenerators(comp!, cancellationToken).GetRunResult();
-            ImmutableArray<Diagnostic> generatorDiagnostics = generatorResults.Diagnostics.RemoveAll(d => d.Severity <= DiagnosticSeverity.Hidden);
-            if (generatorDiagnostics.Length != 0)
+            CultureInfo origCulture = CultureInfo.CurrentCulture;
+            CultureInfo.CurrentCulture = s_cultureWithMinusNegativeSign;
+            GeneratorDriverRunResult generatorResults;
+            ImmutableArray<Diagnostic> generatorDiagnostics;
+            try
             {
-                throw new ArgumentException(
-                    string.Join(Environment.NewLine, generatorResults.GeneratedTrees.Select(t => NumberLines(t.ToString()))) + Environment.NewLine +
-                    string.Join(Environment.NewLine, generatorDiagnostics));
+                generatorResults = s_generatorDriver.RunGenerators(comp!, cancellationToken).GetRunResult();
+                generatorDiagnostics = generatorResults.Diagnostics.RemoveAll(d => d.Severity <= DiagnosticSeverity.Hidden);
+                if (generatorDiagnostics.Length != 0)
+                {
+                    throw new ArgumentException(
+                        string.Join(Environment.NewLine, generatorResults.GeneratedTrees.Select(t => NumberLines(t.ToString()))) + Environment.NewLine +
+                        string.Join(Environment.NewLine, generatorDiagnostics));
+                }
+            }
+            finally
+            {
+                CultureInfo.CurrentCulture = origCulture;
             }
 
             // Compile the assembly to a stream

Original file line number	Diff line number	Diff line change
`@@ -2573,7 +2573,7 @@ void EmitCapture(RegexNode node, RegexNode? subsequent = null)`
`2573`	`2573`	`}`
`2574`	`2574`
`2575`	`2575`	`writer.WriteLine();`
`2576`		`- writer.WriteLine($"base.TransferCapture({capnum}, {uncapnum}, {startingPos}, pos);");`
	`2576`	`+ writer.WriteLine($"base.TransferCapture({capnum.ToString(CultureInfo.InvariantCulture)}, {uncapnum}, {startingPos}, pos);");`
`2577`	`2577`	`}`
`2578`	`2578`
`2579`	`2579`	`if (isAtomic \|\| !childBacktracks)`