Rich text editor: Editing code blocks removes leading whitespace

[personalizedrefrigerator]

Operating system

Linux

Joplin version

2.14.20, 3.0.2

Desktop version info

Joplin 3.0.2 (dev, linux)

Client ID: c4ee1ffb618e4576a7bf7477a5b942e6
Sync Version: 3
Profile Version: 47
Keychain Supported: No

Revision: 9fe3154

Backup: 1.4.1
Freehand Drawing: 2.9.1
RevealJS Integration: 0.12.0

Current behaviour

Currently, when editing a code block in the rich text editor, leading whitespace on the first line is lost.

rte-removes-leading-spaces.mp4

For example,

1. Create a new note with the following content (markdown editor)

   ```foo
       line 1
       line 2
       line 3
   ```

2. Switch to the rich text editor
3. Double-click to edit the code block
4. Add a new line (e.g. "line 4")
5. Click "ok" to close the editor window
6. Observe that the first line has lost its indentation

Expected behaviour

Code blocks should not lose indentation when editing them in the rich text editor.

Logs

No response

[personalizedrefrigerator]

See also https://discourse.joplinapp.org/t/preserve-leading-whitespace-in-fences-in-rich-text-editor/37637/2