`coc#prompt#getchar()` break if `lmap` with `<expr>`

[ZSaberLv0]

Result from CocInfo

vim version: NVIM v0.6.1
node version: v18.0.0
coc.nvim version: 0.0.80-0479ccf5 2022-04-25 01:27:15 +0800
coc.nvim directory: /Users/mac/.vim/bundle/coc.nvim
term: xterm-256color
platform: darwin

Describe the bug

coc#prompt#getchar() break if lmap with <expr>

Reproduce the bug

• Create file mini.vim with：

  " coc's common config
  filetype plugin indent on
  syntax on
  set nocompatible
  let g:plug_home = $HOME . '/.vim/bundle'
  let g:plug_url_format = 'https://github.com/%s'
  execute 'source ' . g:plug_home . '/vim-plug/plug.vim'
  silent! call plug#begin()
  Plug 'junegunn/vim-plug'
  Plug 'neoclide/coc.nvim', {'branch': 'release'}
  call plug#end()
  
  " lmap config
  function! Test()
  return 'a'
  endfunction
  lnoremap <expr> a Test()

• Start (neo)vim with command: vim -u mini.vim

• toggle iminsert by: enter insert mode and press <c-6> (:h i_CTRL-^)

• :CocList outline and input a, would result Test() as plain input

---

• related issue: https://github.com/ZSaberLv0/ZFVimIM/issues/43

• a simple workaround: check result of maparg() and ignore expr type, but not sure whether it has other side effects

  https://github.com/neoclide/coc.nvim/blob/master/autoload/coc/prompt.vim#L97

[persytry]

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