Unreasonable line-editor behaviour

Summary

The line-editor used in GHCi is unusably broken.

Steps to reproduce

Run GHCi, then type abc and press Ctrl+A (or the Home key). The visible cursor will now be over the c. Pressing the right arrow key three times moves the visible cursor far beyond the visible text. Repeating this process will continually shift rightward the position that the line-editor sees as the beginning of the line. The cursor location and the visible text are out of sync.

Expected behavior

The press of Ctrl+A should result in the cursor moving to the beginning of the line, rather than just one character to the left of where it was.

Environment

• GHC version used: 8.10.5

Optional:

• Operating System: macOS 11.3
• System Architecture: arm64