Runaway cursor when using escape+undo in vi mode

[krobelus]

Steps

1. fish_vi_key_bindings
2. bind -m insert u undo
3. Press Alt+u

The cursor jumps to the first character of the line (inside the prompt).

[faho]

Figured it out: alt+u is \eu, which is executed as two bindings:

• Escape, which switches to normal mode and does "repaint-mode"
• "u", which then does undo

The issue is that repaint-mode does a screen.reset_line() but then only does a repaint if it is "needed" - well, it is needed because we just reset the line, moving the cursor to the beginning.

One possibility is to skip the repaint and cursor move if the mode prompt buffer didn't change.

fish-shell/src/reader.cpp

Line 3571 in 3ce67ec

if (this->is_repaint_needed()) this->layout_and_repaint(L"mode");

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As a sidenote: Repainting is always done with 5 lines of code, and I'm not entirely sure which of these are necessary and which are cargo-culting. It would be cool if this was just 1 line that did the right thing.