feat(nvim): ex-commands :! integration (#4)

* feat(nvim): ex-commands `:!` integration

Settings with documentation for using Nushell for:
- filtering buffer content through external commands.
    Now `:!` `:r!` `:w !` work just fine.
- vim diff mode with external diff commands
    `nvim -d {file1} {file2}` with `set diffopt-=internal`
- `:make` and quickfix buffer with `makeprg`

* fix(nvim): reword comments for options

- better clarifications for shelltemp shellredir and shellpipe
- remove extra `NOTE:`

Author: 39555

nvim/init.lua

@@ -21,15 +21,43 @@ if not vim.loop.fs_stat(lazypath) then
 end ---@diagnostic disable-next-line: undefined-field
 vim.opt.rtp:prepend(lazypath)
 
--- INFO: settings to set nushell as the shell
-vim.opt.shellredir = "--stdin < %s"
-vim.opt.shellcmdflag = "-c"
-vim.opt.shellquote = ""
-vim.opt.shellxquote = " "
-vim.opt.shellxescape = ""
+
+-- INFO: settings to set nushell as the shell for the :! command
+-- --
+-- path to the Nushell executable
 vim.opt.sh = "nu"
 
--- NOTE: you can instead uncomment the following to for instance provide custom config paths
+-- WARN: disable the usage of temp files for shell commands
+-- because Nu doesn't support `input redirection` which Neovim uses to send buffer content to a command:
+--      `{shell_command} < {temp_file_with_selected_buffer_content}`
+-- When set to `false` the stdin pipe will be used instead.
+-- NOTE: some info about `shelltemp`: https://github.com/neovim/neovim/issues/1008
+vim.opt.shelltemp = false
+
+-- string to be used to put the output of shell commands in a temp file
+-- 1. when 'shelltemp' is `true` 
+-- 2. in the `diff-mode` (`nvim -d file1 file2`) when `diffopt` is set 
+--    to use an external diff command: `set diffopt-=internal`
+vim.opt.shellredir = "out+err> %s"
+
+-- flags for nu:
+-- * `--stdin`       redirect all input to -c
+-- * `--no-newline`  do not append `\n` to stdout
+-- * `--commands -c` execute a command
+vim.opt.shellcmdflag = "--stdin --no-newline -c"
+
+-- disable all escaping and quoting
+vim.opt.shellxescape = ""
+vim.opt.shellxquote = ""
+vim.opt.shellquote = ""
+
+-- string to be used with `:make` command to:
+-- 1. save the stderr of `makeprg` in the temp file which Neovim reads using `errorformat` to populate the `quickfix` buffer
+-- 2. show the stdout, stderr and the return_code on the screen
+-- NOTE: `ansi strip` removes all ansi coloring from nushell errors
+vim.opt.shellpipe = '| complete | update stderr { ansi strip } | tee { get stderr | save --force --raw %s } | into record'
+
+-- NOTE: you can uncomment the following to for instance provide custom config paths
 -- depending on the OS
 -- In this particular example using vim.env.HOME is also cross-platform