RegexOptions.Multiline not matching text

[VS-ux]

Description

• Using RegexOptions.Multiline on a string with \r\n fails with this regex:
  ^(?:[a-zA-Z]:|\\[\w.]+\[\w.$]+)\(?:[\w]+\)*\w([\w.])+$

Configuration

• .NET Core 3.1
• Windows 10 20180
• x64
• It is not specific to this config.

Regression?

• Did this work in a previous build or release of .NET Core, or from .NET Framework? If you can try a previous release or build to find out, that can help us narrow down the problem. If you don't know, that's OK.
  No.

Other information

• This is a duplicate of RegexOptions.Multiline should be same as line by line #40566. In that test, I thought it was due to the \r match failing. However, in this test, I'm using \r\n

string textToMatch = "C:\\testpath1.txt\r\nC:\\testpath2.txt";
int matchCount = Regex.Matches(textToMatch, @"^(?:[a-zA-Z]\:|\\\\[\w\.]+\\[\w.$]+)\\(?:[\w]+\\)*\w([\w.])+$", RegexOptions.Compiled | RegexOptions.Multiline).Count;

Console.WriteLine(matchCount); // 1, but if you swap \r\n with \n, it returns 2

[ghost]

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[danmoseley]

Can you please try to minimize the repro code/pattern/text? Like last time, this often makes things clearer.

[VS-ux]

@danmosemsft Hi! The text is just above.
Here is the code to reproduce the issue:

string textToMatch = "C:\\testpath1.txt\r\nC:\\testpath2.txt";
int matchCount = Regex.Matches(textToMatch, @"^(?:[a-zA-Z]\:|\\\\[\w\.]+\\[\w.$]+)\\(?:[\w]+\\)*\w([\w.])+$", RegexOptions.Compiled | RegexOptions.Multiline).Count;

Console.WriteLine(matchCount); // 1, but if you swap \r\n with \n, it returns 2

[danmoseley]

Yes thanks I see that I’m asking you to minimize the pattern please.

[VS-ux]

Oops, sorry. Here is the simplified version:

string textToMatch = "hello\r\nasd";
int matchCount = Regex.Matches(textToMatch, @"^[a-z]+$", RegexOptions.Compiled | RegexOptions.Multiline).Count;

Console.WriteLine(matchCount); // 1, but if you swap \r\n with \n, it returns 2

The issue is that RegexOptions.Multiline doesn't get rid of \r so it matches 1 character too much.

[danmoseley]

Right, it only understands \n. The complete description is here:
#25598 (comment)
Do the docs need clarification? Feel free to submit a PR if so (pencil icon in top right of doc).

I’m going to close this as it’s working as designed. The AnyNewLine feature would help!