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

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Issue Details

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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

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':

runtime/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexParser.cs

Lines 2060 to 2062 in aac729f

	private static ReadOnlySpan<byte> Category => new byte[] {
	// 0 1 2 3 4 5 6 7 8 9 A B C D E F 0 1 2 3 4 5 6 7 8 9 A B C D E F
	0, 0, 0, 0, 0, 0, 0, 0, 0, X, X, 0, X, X, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

We might want to dig a tad deeper, as it feels a little deliberate that cell was left as 0 rather than X.