MultiLineTextInput widget persistently takes on rich formatting on a paste operation

[kcoombs]

Describe the bug

When pasting rich-formatted text into a MultiLineTextInput widget, the widget takes on the rich formatting.

Steps to reproduce

1. Launch a Toga application that includes a MultiLineTextInput widget. e.g., from the Toga repository, examples/multilinetextinput.
2. Copy rich-formatted text from another application, e.g., MS Word, TextEdit, a web browser.
3. Paste into the MultiLineTextInput widget.
4. Rich-formatting is preserved in the MultiLineTextInput widget. The formatting persists even when clearing the value (e.g., "clear" button in the Toga multilinetextinput example).

Expected behavior

While rich formatting may be desirable in some situations, I'd expect the default behavior to be displaying only plain text, like a TextInput widget.

Screenshots

Before paste:

Rich text (TextEdit):

After paste:

After clear:

Environment

• Operating System:

  • MacOS Sequoia 15.1
  • Windows 11
  • Others???

• Python version:

  • 3.12.7

• Software versions:

  • Toga: 0.4.8

Logs

Additional context

No response

[freakboy3742]

Confirming this definitely isn't the intended behavior. I'm guessing we've missed an option when configuring the native text widgets.

Not sure if this also affects GTK, iOS or Android; seems highly plausible it might be an issue on GTK.

[kcoombs]

As least so far as MacOS goes, this seems to prevent MultiLineTextInput from taking rich-formatted text on a paste:

diff --git a/cocoa/src/toga_cocoa/widgets/multilinetextinput.py b/cocoa/src/toga_cocoa/widgets/multilinetextinput.py
index c651fa8e4..e908ecb6d 100644
--- a/cocoa/src/toga_cocoa/widgets/multilinetextinput.py
+++ b/cocoa/src/toga_cocoa/widgets/multilinetextinput.py
@@ -36,6 +36,7 @@ class MultilineTextInput(Widget):

         # Create the actual text widget
         self.native_text = TogaTextView.alloc().init()
+        self.native_text.setRichText_(False)
         self.native_text.interface = self.interface
         self.native_text.delegate = self.native_text

See https://developer.apple.com/documentation/appkit/nstextview/1449538-richtext.