Emacs difficulties in linux console with ncurses-6.3 caused by kcbt=\E^I.

[Alan Mackenzie]

Hello, ncurses!

I'm writing as a member of the Emacs development team.

In the recent change from ncurses-6.2 to ncurses-6.3, the following
change was make in the linux console terminfo:

--- Infocmp-linux-6.2   2022-05-04 20:16:01.609557894 +0000
+++ infocmp-linux-6.3   2022-05-04 20:09:02.046581014 +0000
@@ -14,7 +14,7 @@
        home=\E[H, hpa=\E[%i%p1%dG, ht=^I, hts=\EH, ich=\E[%p1%d@,
        ich1=\E[@, il=\E[%p1%dL, il1=\E[L, ind=\n,
        
initc=\E]P%p1%x%p2%{255}%*%{1000}%/%02x%p3%{255}%*%{1000}%/%02x%p4%{255}%*%{1000}%/%02x,
-       kb2=\E[G, kbs=^?, kcbt=\E[Z, kcub1=\E[D, kcud1=\E[B,
+       kb2=\E[G, kbs=^?, kcbt=\E^I, kcub1=\E[D, kcud1=\E[B,
        kcuf1=\E[C, kcuu1=\E[A, kdch1=\E[3~, kend=\E[4~, kf1=\E[[A,
        kf10=\E[21~, kf11=\E[23~, kf12=\E[24~, kf13=\E[25~,
        kf14=\E[26~, kf15=\E[28~, kf16=\E[29~, kf17=\E[31~,

We now have kcbt=\E^I.

In Emacs on the Linux console, our use of terminfo now has the effect of
replacing the M-tab keysequence with backtab.  This make several
important key-bindings unusable.  (The backtab binding is also used, but
is perhaps a little less important.)

Also, this would seem to be a difficult problem for a normal user to
diagnose, and difficult also to fix.

May I ask why this change was made to the linux terminal?  Is there any
possibiliy it might be reverted?

Is there perhaps some strategy we could use in Emacs (C code) which would
work around this problem with using ugly ad-hoc code?

Thanks in advance!

-- 
Alan Mackenzie (Nuremberg, Germany).