Arrow key inputs are ignored on ENABLE_VIRTUAL_TERMINAL_INPUT enabled windows console #914

Symptoms similar to those described in #903 also occur in mswin/mingw.
ENABLE_VIRTUAL_TERMINAL_INPUT is normally disabled, but it may be enabled by other processes sharing the console, and it is possible that it is not reset due to a crash or other issue.

Step to reproduce

in irb

Reline::IOGate.instance_exec do
  m = "\0"*4; @GetConsoleMode.call(@hConsoleInputHandle, m);
  @SetConsoleMode.call(@hConsoleInputHandle, m.unpack1("L") | 0x200)
end

Or, for more flexibility,

irb(main):001> Reline::IOGate.class
=> Reline::Windows
irb(main):002* def set_vt_input(f)
irb(main):003*   Reline::IOGate.instance_exec do
irb(main):004*     m = "\0"*4; @GetConsoleMode.call(@hConsoleInputHandle, m);
irb(main):005*     mode = m.unpack1("L")
irb(main):006*     puts "old mode: #{mode.to_s(16)}"
irb(main):007*     new_mode = (mode & ~0x200) | (f ? 0x200 : 0)
irb(main):008*     @SetConsoleMode.call(@hConsoleInputHandle, new_mode)
irb(main):009*     puts "new mode: #{new_mode.to_s(16)}"
irb(main):010*   end
irb(main):011> end
=> :set_vt_input
irb(main):012> set_vt_input(true)
old mode: 1f7
new mode: 3f7
=> nil
irb(main):013> # => cursor movement using the arrow keys is disabled
irb(main):014> set_vt_input(false)
old mode: 3f7
new mode: 1f7
=> nil
irb(main):015> # => cursor movement using the arrow keys is enabled

Under the hood

Reline::Windows converts input key events to the output of getwch() rather than VT sequences (presumably to preserve the specifications from the early stages of development).
When ENABLE_VIRTUAL_TERMINAL_INPUT is enabled, Reline receives input that can be represented as VT sequences as characters rather than events, so no conversion to getwch() code takes place.
Since Reline::Windows bases its key bindings on getwch() codes, it cannot recognize input in the form of VT sequences.

Options for a Solution

1. Add key bindings for VT sequences to Reline::Windows
2. Stop using the getwch() code and have Reline::Windows convert key events to VT sequences

Although option 2 introduces more changes, since WSL coexists in Windows environments, this approach is preferable because it allows for the use of a common configuration.