Regex parser doesn't ignore vertical tabs in patter when using RegexOptions.IgnorePatternWhiteSpace

[joperezr]

While porting PCRE2 tests suite, one of the failing tests is:

bool isMatch = Regex.IsMatch("ab", "a\vb", RegexOptions.IgnorePatternWhitespace);
Assert.True(isMatch);

This should probably be true and match other engines like PCRE as \v character should be ignored as whitespace and just have the pattern be ab

cc: @stephentoub

[ghost]

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Issue Details

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While porting PCRE2 tests suite, one of the failing tests is: ```c# bool isMatch = Regex.IsMatch("ab", "a\vb", RegexOptions.IgnorePatternWhitespace); Assert.True(isMatch); ``` This should probably be true and match other engines like PCRE as `\v` character should be ignored as whitespace and just have the pattern be `ab` cc: @stephentoub

Author:	joperezr
Assignees:	-
Labels:	`area-System.Text.RegularExpressions`
Milestone:	-

[stephentoub]

This does seem like a bug; char.IsWhitespace('\v') is true, as is Regex.IsMatch("\v", @"\s"). Presumably it'd be as simple as changing the Category[0xB] value in the following table to be 'X': https://github.com/dotnet/runtime/blob/aac729ff906a31f327823587748687c0308a4043/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexParser.cs#L2060-L2062 We might want to dig a tad deeper, as it feels a little deliberate that cell was left as 0 rather than X.