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Fix: Allow inline regex options in conditional expression branches #124699

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Fix: Allow inline regex options in conditional expression branches #124699

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7eb0fa8
Fix: Allow inline regex options in conditional expression branches
danmoseley Feb 21, 2026
0b3f1a8
Add negative test for inline options as conditional test expression
danmoseley Feb 21, 2026
3e9780e
Clarify that (?(?i)yes|no) not throwing on netfx is a parser bug
danmoseley Feb 23, 2026
7690fdd
Improve comment describing inline options restriction in conditional …
danmoseley Feb 23, 2026
5424aa0
Add test for inline options inside conditional test expression
danmoseley Feb 23, 2026
367253f
Remove issue link from test comment
danmoseley Feb 23, 2026
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5 changes: 3 additions & 2 deletions ...ibraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexParser.cs
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Expand Up @@ -1000,8 +1000,9 @@ private RegexNode ScanReplacement()
--_pos;

nodeType = RegexNodeKind.Group;
// Disallow options in the children of a testgroup node
if (_group!.Kind != RegexNodeKind.ExpressionConditional)
// While parsing the test of a conditional (ExpressionConditional with no children yet),
// disallow inline options; allow them once the test has been parsed and in the yes/no branches.
if (_group!.Kind != RegexNodeKind.ExpressionConditional || _group.ChildCount() > 0)
{
ScanOptions();
}
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10 changes: 10 additions & 0 deletions src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs
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Expand Up @@ -898,6 +898,16 @@ public static IEnumerable<object[]> Match_MemberData()
yield return (@"(?(\w+)\w+)dog", "catdog", RegexOptions.None, 0, 6, true, "catdog");
yield return (@"(?(abc)\w+|\w{0,2})dog", "catdog", RegexOptions.None, 0, 6, true, "atdog");
yield return (@"(?(abc)cat|\w{0,2})dog", "catdog", RegexOptions.None, 0, 6, true, "atdog");

// Inline options inside conditional branches
yield return (@"(?(cat)(?i)CAT|dog)", "cat", RegexOptions.None, 0, 3, true, "cat");
yield return (@"(?(cat)(?i)cat|dog)", "dog", RegexOptions.None, 0, 3, true, "dog");
yield return (@"(?(cat)cat|(?i)dog)", "DOG", RegexOptions.None, 0, 3, true, "DOG");
yield return (@"(?(cat)(?i:CAT)|dog)", "cat", RegexOptions.None, 0, 3, true, "cat");
yield return (@"(?(?=cat)(?i)CAT|dog)", "cat", RegexOptions.None, 0, 3, true, "cat");
yield return (@"(cat)?(?(1)(?i)dog|pig)", "catDOG", RegexOptions.None, 0, 6, true, "catDOG");
yield return (@"(cat)?(?(1)(?i)dog|pig)", "pig", RegexOptions.None, 0, 3, true, "pig");
yield return (@"(?((?i)cat)CAT|dog)", "CAT", RegexOptions.None, 0, 3, true, "CAT");
yield return ("(a|ab|abc|abcd)d", "abcd", RegexOptions.RightToLeft, 0, 4, true, "abcd");

yield return ("(?>(?:a|ab|abc|abcd))d", "abcd", RegexOptions.None, 0, 4, false, string.Empty);
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1 change: 1 addition & 0 deletions ...aries/System.Text.RegularExpressions/tests/FunctionalTests/RegexParserTests.netcoreapp.cs
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Expand Up @@ -26,6 +26,7 @@ public partial class RegexParserTests
[InlineData(@"(?(?X))", RegexOptions.None, RegexParseError.InvalidGroupingConstruct, 5)]
[InlineData(@"(?(?n))", RegexOptions.None, RegexParseError.InvalidGroupingConstruct, 5)]
[InlineData(@"(?(?m))", RegexOptions.None, RegexParseError.InvalidGroupingConstruct, 5)]
[InlineData(@"(?(?i)yes|no)", RegexOptions.None, RegexParseError.InvalidGroupingConstruct, 5)] // does not throw on .NET Framework, but that is a parser bug there
[InlineData("(?<-", RegexOptions.None, RegexParseError.InvalidGroupingConstruct, 3)]
[InlineData("(?<-", RegexOptions.IgnorePatternWhitespace, RegexParseError.InvalidGroupingConstruct, 3)]
[InlineData(@"^[^<>]*(((?'Open'<)[^<>]*)+((?'Close-Open'>)[^<>]*)+)*(?(Open)(?!))$", RegexOptions.None, null)]
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