Cannot get the expected result when set "\r\n" to RichTextBox.Text property

[John-Qiao]

• .NET Core Version:
  5.0.0-rc.1.20425.1

• Have you experienced this same bug with .NET Framework?:
  No

More info:

1. This issue does not occur in .NET Framework.
2. This issue does not occur in .NET Core 3.1 and .NET 5.0 Preview 8. It's a regression issue in 5.0.0-rc.1.20425.1.
3. It maybe caused by this PR: 3726

Problem description:

Cannot get the expected result in RichTextBox.Text property when included the "\r\n" in it.

Expected behavior:
Should get the below value from RichTextBox.Text property. Like it works in .NET Framework and previous version of .NET Core SDK.

Minimal repro:

1. Launch the attached project in VS.
2. Run it and observe the value for richTextBox1.Text in debugging.
   Issue1-TestApp.zip

[merriemcgaw]

We may need to revert #3726 if we can't find a better solution.

[RussKie]

@JeremyKuhne I think this is the expected RichEdit behaviour, the docs state that the default flag does not translate \r -> \r\n:

The original implementation went like this:
get_Text -> StreamOut(SF.TEXT | SF.UNICODE) -> StreamOut(..., includeCrLfs: false) which would normalise EoL to \n.

In fact, while setting Text we're normalising EoL to \n:

• https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/RichTextBox.cs,3052

• winforms/src/System.Windows.Forms/src/System/Windows/Forms/RichTextBox.cs

  Line 3007 in 6d1700b

  cookieVal |= TEXTLF;

I suppose we have few options:
1. use the GT_USECRLF flag to convert from \r to \r\n, and document the new behavior (and stop here); or
2. in addition to the above, replace \r\n -> \n.