Mouse not working inside Alacritty

Question

I am facing an issue with my vim. The mouse isn't working. I have set set mouse=a in my vimrc. I have checked it inside vim that the mouse value is set to "a". But it's still not working. What can I do?

N.B. I have also tried set mouse+=a which also doesn't work.

I am using Ubuntu 20.04 and Vim 8.1.2269 and my terminal is Alacritty.

~ ➜ vim --version
VIM - Vi IMproved 8.1 (2018 May 18, compiled Apr 15 2020 06:40:31)
Included patches: 1-2269
Modified by team+vim@tracker.debian.org
Compiled by team+vim@tracker.debian.org
Huge version with GTK3 GUI.  Features included (+) or not (-):
+acl               -farsi             -mouse_sysmouse    -tag_any_white
+arabic            +file_in_path      +mouse_urxvt       +tcl
+autocmd           +find_in_path      +mouse_xterm       +termguicolors
+autochdir         +float             +multi_byte        +terminal
-autoservername    +folding           +multi_lang        +terminfo
+balloon_eval      -footer            -mzscheme          +termresponse
+balloon_eval_term +fork()            +netbeans_intg     +textobjects
+browse            +gettext           +num64             +textprop
++builtin_terms    -hangul_input      +packages          +timers
+byte_offset       +iconv             +path_extra        +title
+channel           +insert_expand     +perl              +toolbar
+cindent           +job               +persistent_undo   +user_commands
+clientserver      +jumplist          +postscript        +vartabs
+clipboard         +keymap            +printer           +vertsplit
+cmdline_compl     +lambda            +profile           +virtualedit
+cmdline_hist      +langmap           -python            +visual
+cmdline_info      +libcall           +python3           +visualextra
+comments          +linebreak         +quickfix          +viminfo
+conceal           +lispindent        +reltime           +vreplace
+cryptv            +listcmds          +rightleft         +wildignore
+cscope            +localmap          -ruby              +wildmenu
+cursorbind        +lua               +scrollbind        +windows
+cursorshape       +menu              +signs             +writebackup
+dialog_con_gui    +mksession         +smartindent       +X11
+diff              +modify_fname      +sound             -xfontset
+digraphs          +mouse             +spell             +xim
+dnd               +mouseshape        +startuptime       +xpm
-ebcdic            +mouse_dec         +statusline        +xsmp_interact
+emacs_tags        +mouse_gpm         -sun_workshop      +xterm_clipboard
+eval              -mouse_jsbterm     +syntax            -xterm_save
+ex_extra          +mouse_netterm     +tag_binary
+extra_search      +mouse_sgr         -tag_old_static
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
  system gvimrc file: "$VIM/gvimrc"
    user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
    system menu file: "$VIMRUNTIME/menu.vim"
  fall-back for $VIM: "/usr/share/vim"
Compilation: gcc -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_GTK  -pthread -I/usr/include/gtk-3.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -I/usr/include/gtk-3.0 -I/usr/include/gio-unix-2.0 -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/fribidi -I/usr/include/harfbuzz -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -Wdate-time  -g -O2 -fdebug-prefix-map=/build/vim-iU6mZD/vim-8.1.2269=. -fstack-protector-strong -Wformat -Werror=format-security -D_REENTRANT -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
Linking: gcc   -Wl,-E  -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -Wl,--as-needed -o vim   -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -lharfbuzz -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lSM -lICE -lXpm -lXt -lX11 -lXdmcp -lSM -lICE  -lm -ltinfo -lnsl  -lselinux  -lcanberra -lacl -lattr -lgpm -ldl  -L/usr/lib -llua5.2 -Wl,-E  -fstack-protector-strong -L/usr/local/lib  -L/usr/lib/x86_64-linux-gnu/perl/5.30/CORE -lperl -ldl -lm -lpthread -lcrypt  -L/usr/lib/python3.8/config-3.8-x86_64-linux-gnu -lpython3.8 -lcrypt -lpthread -ldl -lutil -lm -lm -L/usr/lib/x86_64-linux-gnu -ltcl8.6 -ldl -lz -lpthread -lm

Answer 1

You can add to your Alacritty configuration file (default: ~/.config/alacritty/alacritty.yml):

env:
  TERM: xterm-256color

Answer 2

There are several ways Vim can recognize mouse events in the Terminal, this is why the --version has a whole bunch of flags starting with mouse: mouse_dec, mouse_xterm, mouse_urxvt, etc. There are all sorts of historical reasons for this.

Judging from this issue, this issue, and several others it seems that Vim doesn't detect the correct method for Alacritty, which should be "sgr". You can explicitly tell Vim which method to use with set ttymouse=sgr.

Personally, I would wrap this in a $TERM check in my vimrc, so it doesn't force this if you try out a different terminal or the like:

if $TERM == 'alacritty'
  set ttymouse=sgr
endif

Also see this Vim issue.