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I have the following code in my ~/.zshrc:

autoload -Uz edit-command-line

zle -N edit-command-line

bindkey '^X^E' edit-command-line

It binds the edit-command-line zle widget to the keysequence C-x C-e.
The widget is described in man zshcontrib (section ZLE FUNCTIONS, subsection Widgets):

edit-command-line
Edit the command line using your visual editor, as in ksh.

          bindkey -M vicmd v edit-command-line

The purpose is to be able to edit the current shell command line, in the default editor, by pressing C-x C-e, similar to what the readline function edit-and-execute-command does (man bash, section READLINE, subsection Commands for Manipulating the History).

edit-and-execute-command (C-xC-e)
Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts
to invoke $VISUAL, $EDITOR, and emacs as the editor, in that order.

My default editor is Vim 8.1 (patches 1-538 included).
I have Vim mappings, using the keys C-h, C-j, C-k, C-l, to move the focus to neighbour windows.
They can be boiled down to:

nnoremap <c-h> :<c-u>wincmd h<cr>

nnoremap <c-j> :<c-u>wincmd j<cr>

nnoremap <c-k> :<c-u>wincmd k<cr>

nnoremap <c-l> :<c-u>wincmd l<cr>

They all work as expected in a regular Vim instance (started by executing $ vim).
But C-j doesn't work as expected when Vim was started by edit-command-line.

When I press C-x C-e while on the shell command line, zsh starts Vim. If I split the window by executing :split, then press C-k to move to the top window, I get two windows, and the focus is moved to the top one. But then, if I press C-j to get back to the bottom window, nothing happens.

I don't know whether it's the cause of the issue, but if I try to insert a literal C-j in a Vim buffer (by pressing C-v C-j), ^M is displayed (the caret notation for a carriage return). In a regular Vim instance (started by executing $ vim), inserting a literal C-j results in a character whose caret notation is ^@ (a NUL).

I can reproduce the issue with this minimal ~/.zshrc:

export EDITOR=vim

autoload -Uz edit-command-line

zle -N edit-command-line

bindkey '^X^E' edit-command-line

And this minimal ~/.vimrc:

nnoremap <c-j> :echom 'C-j has been pressed'<cr>

Pressing C-x C-e on the zsh command line starts Vim, then pressing C-j should print and log the message:

C-j has been pressed

But nothing happens.

I can't reproduce the issue in bash, nor with Neovim (v0.3.2-752-g4d7c7f9).
Besides, inserting a literal C-j in Vim, when the latter was started from bash after pressing C-x C-e, results in a NUL (^@). Same thing when Neovim is started from bash or zsh after pressing C-x C-e.

┌────────┬──────┬─────┐

│        │ bash │ zsh │

├────────┼──────┼─────┤

│ Vim    │ ^@   │ ^M  │

├────────┼──────┼─────┤

│ Neovim │ ^@   │ ^@  │

└────────┴──────┴─────┘

I thought that maybe some Vim terminal option was not properly configured, so I captured the output of:

:set termcap

from Vim started by $ vim, and from Vim started by C-x C-e.
But the output is identical in both cases:

--- Terminal codes ---



  t_AL=^[[%p1%dL      t_DL=^[[%p1%dM      t_mr=^[[7m          t_se=^[[27m         t_us=^[[4m

  t_al=^[[L           t_dl=^[[M           t_ms=y              t_Sf=               t_ut=

  t_bc=               t_EC=               t_nd=^[[C           t_SH=               t_vb=^[g

  t_BE=               t_EI=^[[2 q         t_op=^[[39;49m      t_SI=^[[6 q         t_vi=^[[?25l

  t_BD=               t_fs=^G             t_RF=               t_Si=               t_VS=

  t_cd=^[[J           t_GP=               t_RB=               t_so=^[[7m          t_vs=^[[34l

  t_ce=^[[K           t_IE=               t_RC=               t_SR=^[[4 q         t_WP=

  t_cl=^[[H^[[J       t_IS=               t_RI=^[[%p1%dC      t_sr=^[M            t_WS=

  t_Ce=               t_ke=^[[?1l^[>      t_Ri=               t_ST=               t_xn=y

  t_Co=256            t_ks=^[[?1h^[=      t_RS=               t_Te=               t_xs=

  t_CS=               t_le=^H             t_RT=               t_Ts=               t_ZH=^[[3m

  t_CV=               t_mb=^[[5m          t_RV=               t_ts=^0;          t_ZR=^[[23m

  t_da=               t_md=^[[1m          t_Sb=               t_u7=               t_8f=

  t_db=               t_me=^[[0m          t_SC=               t_ue=^[[24m         t_8b=

  t_AB=^[[%?%p1%{8}%<%t4%p1%d%e%p1%{16}%<%t10%p1%{8}%-%d%e48;5;%p1%d%;m

  t_AF=^[[%?%p1%{8}%<%t3%p1%d%e%p1%{16}%<%t9%p1%{8}%-%d%e38;5;%p1%d%;m

  t_cm=^[[%i%p1%d;%p2%dH

  t_Cs=^12;%p1%s^G

  t_cs=^[[%i%p1%d;%p2%dr

  t_te=^[[2 q^[[?1004l^[[?1049l

  t_ti=^[[2 q^[[?1004h^[[?1049h

  t_ve=^[[34h^[[?25h



--- Terminal keys ---



t_#2 <S-Home>    ^[[1;2H   t_k6 <F6>        ^[[17~    t_kh <Home>      ^[[1~          <ð>        ^[p

t_#4 <S-Left>    ^[[1;2D   t_k7 <F7>        ^[[18~    t_kl <Left>      ^[OD           <ô>        ^[t

t_%i <S-Right>   ^[[1;2C   t_k8 <F8>        ^[[19~    t_kr <Right>     ^[OC           <õ>        ^[u

t_*7 <S-End>     ^[[1;2F   t_k9 <F9>        ^[[20~    t_ku <Up>        ^[OA           <ù>        ^[y

t_@7 <End>       ^[[4~     t_k; <F10>       ^[[21~         <á>        ^[a            <ú>        ^[z

t_F1 <F11>       ^[[23~    t_kB <S-Tab>     ^[[Z           <â>        ^[b            <Mouse>     ^[[M

t_F2 <F12>       ^[[24~    t_kD <Del>       ^[[3~          <ä>        ^[d            <S-F18>     ^[[O

t_k1 <F1>        ^[OP      t_kI <Insert>    ^[[2~          <å>        ^[e            <S-F19>     ^[[I

t_k2 <F2>        ^[OQ      t_kN <PageDown>  ^[[6~          <æ>        ^[f            <xUp>       ^[[1;*A

t_k3 <F3>        ^[OR      t_kP <PageUp>    ^[[5~          <ç>        ^[g            <xDown>     ^[[1;*B

t_k4 <F4>        ^[OS      t_kb <BS>        ^?             <í>        ^[m            <xLeft>     ^[[1;*D

t_k5 <F5>        ^[[15~    t_kd <Down>      ^[OB           <î>        ^[n            <xRight>    ^[[1;*C

The output of $ stty -a is also identical in bash and zsh:

speed 38400 baud; rows 33; columns 119; line = 0;

intr = ^C; quit = ^; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;

eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;

werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;

-parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts

-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl -ixon -ixoff

-iuclc -ixany -imaxbel iutf8

opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0

isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt

echoctl echoke -flusho -extproc

I'm using zsh 5.6.2-dev-1 (x86_64-pc-linux-gnu).

Is there a Vim or zsh option which should be set to prevent Vim from translating C-j into C-m when started by the zle widget edit-command-line?

If you set your $EDITOR to a script or function that does stty -a, you'll notice that the terminal settings at the time vim is called by that edit-command-line are those of zle (where inlcr which causes the terminal device driver to translate NL to CR is on among other things).

^J is the newline character, so binding it is a bit delicate.

Here, you can work around it by defining a vim function as:

vim() STTY=sane command vim "$@"

Or add edit the STTY=sane (or STTY=-inlcr) to edit-command-line.