Readline -- cannot bind to both Ctrl-tab and tab at the same time?

[Cameron Simpson]

On 29Jun2015 11:36, Chris Angelico <rosuav at gmail.com> wrote:
>On Mon, Jun 29, 2015 at 4:55 AM, Steven D'Aprano <steve at pearwood.info> wrote:
>> Try Ctrl-TAB again, and you'll get "raise" instead of "import".
>>
>> Can anyone else replicate this issue?
>>
>> Is this a Python issue, a problem with the terminal I am using, or readline
>> in general?
>
>Confirmed with Python 3.6 on Debian Jessie. Delving into Laura's
>suggestion that it's a readline problem, I came across this:
>
>http://stackoverflow.com/questions/12044574/getting-complete-and-menu-complete-to-work-together
>
>Testing with "showkey -a" suggests that tab and ctrl-tab indeed send
>the same bytes. I wonder if there's a way to change terminal type or
>fiddle with terminfo to change this? GUI programs obviously don't have
>this conflation.

Yes, this was my surmise (and expectation, frankly - what did you expect 
ctrl-TAB to send?)  So there is no way for the program in the terminal to 
distinguish one from the other; you will always only get one of your bindings.

I would not expect terminfo to get you anything on its own - it is consulted by 
the receiving program. The sending program (the terminal emulator) needs to be 
configured to send different sequences for TAB and ctrl-TAB. Once that is done, 
_then_ you may be able to augument your terminfo to express this behaviour and 
have readline honour the change.

1: Work backward from the readline internals to find out if it consults a 
terminfo property to find out what ctrl-TAB might be.

2: Decide on what you want ctrl-TAB to send instead of the TAB code.

3: Make a new terminfo clause defining that (for readline's use) and hooking 
onto your old terminfo definition for the rest (tc=other_terminal in termcap, 
possibly the same in terminfo).

4: Configure your terminal emulator to send that sequence.

Regarding 4, with proper old-style X11 terminals you could control all this 
directly with the VT100.Translations properties. Example from my xterm 
Xdefaults file; the leading F1 definition is probably what you want:

  XTerm*.VT100.Translations:  #override \n\
    <KeyPress>F1        : string(0x1b) \n \
    <KeyPress>F10       : secure() \n \
    <KeyPress>KP_End        : scroll-forw(100,page) \n \
    <KeyPress>KP_Prior      : scroll-back(1,halfpage) \n \
    <KeyPress>KP_Next       : scroll-forw(1,halfpage) \n\
    <KeyPress>End       : scroll-forw(100,page) \n \
    Ctrl<KeyPress>Up        : scroll-back(1,line) \n \
    Ctrl<KeyPress>Down      : scroll-forw(1,line) \n\
    <KeyPress>Prior     : scroll-back(1,halfpage) \n \
    <KeyPress>Next      : scroll-forw(1,halfpage) \n\
    Meta<KeyPress>      : string(0x1b) insert() \n\
    Alt<KeyPress>       : string(0x1b) insert() \n\
    <KeyPress>BackSpace     : string(0x08) \n \
    Shift<Btn1Down>     : ignore() \n\
    Shift<Btn1Up>       : insert-selection(PRIMARY,CUT_BUFFER0)\n\
    <Btn2Down>          : ignore() \n\
    <Btn2Up>            : insert-selection(PRIMARY,CUT_BUFFER0)\n\
    Shift<Btn2Down>     : ignore() \n\
    Shift<Btn2Up>       : string("us ") insert-selection(PRIMARY,CUT_BUFFER0) 
string("\n") \n\
    ~Ctrl ~Meta<Btn3Down>   : ignore()\n\
    ~Ctrl ~Meta<Btn3Up>     : ignore()\n
  ! commented out, previous experiments
  ! XTerm*VT100.translations: #override Shift<Key>'F1':insert("hi guys")
  ! XTerm*VT100.translations: #override 
  Ctrl<Key>'U':uphalfscreen()\nCtrl<Key>'D'downhalfscreen()

The new fangled terminals like gnome-terminal or Konsole probably threw that 
stuff out as they threw out all the other normal X11 config hooks, and 
doubtless use their own arcane system. Enjoy.

Cheers,
Cameron Simpson <cs at zip.com.au>

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