build(contrib): add bash completion for nvim #35843

Two versions of the completion function are provided:
1. Uses bash-completion@2, which is the community standard for Bash
  completions; version >= 2.12 offers a more user-friendly experience.
2. Uses only bash built-in syntax and completes options only.

contrib/nvim.bash

@@ -0,0 +1,105 @@
+#!/usr/bin/env bash
+
+# Provides bash completion for "nvim".
+
+if [[ -n ${BASH_COMPLETION_VERSINFO[*]} ]] \
+  && ((BASH_COMPLETION_VERSINFO[0] > 2 || (\
+  BASH_COMPLETION_VERSINFO[0] == 2 && BASH_COMPLETION_VERSINFO[1] >= 12))); then
+  # use bash-completion >= 2.12
+  _comp_nvim() {
+    local cur prev words cword
+    _comp_initialize -n : -- "$@" || return
+
+    case "$prev" in
+      --listen | --server)
+        _comp_compgen_filedir
+
+        if [[ "$cur" != /* ]]; then
+          _comp_compgen_ip_addresses -a
+          compopt -o nospace
+        fi
+
+        return
+        ;;
+    esac
+
+    if [[ "$cur" =~ ^- ]]; then
+      # Infers args from "nvim --help".
+      _comp_compgen_help
+      _comp_compgen -a -- -W "-c -Es -v -h"
+
+      if [[ ${#COMPREPLY[@]} -eq 1 ]]; then
+        case "${COMPREPLY-}" in
+          -o | -O | -p | -V)
+            compopt -o nospace
+            ;;
+        esac
+      fi
+      return
+    fi
+
+    _comp_compgen_filedir
+  } \
+    && complete -F _comp_nvim nvim
+else
+  _comp_nvim() {
+    local cur prev opts
+    COMPREPLY=()
+    cur="${COMP_WORDS[COMP_CWORD]}"
+    prev="${COMP_WORDS[COMP_CWORD - 1]}"
+
+    opts="
+      --cmd
+      -c
+      -l
+      -S
+      -s
+      -u
+      -d
+      -es -Es
+      -h --help
+      -i
+      -n
+      -o
+      -O
+      -p
+      -R
+      -v --version
+      -V
+      --
+      --api-info
+      --clean
+      --embed
+      --headless
+      --listen
+      --remote
+      --server
+      --startuptime
+      "
+
+    if [[ "$cur" =~ ^- ]]; then
+      # shellcheck disable=SC2207
+      COMPREPLY=($(compgen -W "$opts" -- "$cur"))
+
+      if [[ ${#COMPREPLY[@]} -eq 1 ]]; then
+        case "${COMPREPLY-}" in
+          -o | -O | -p | -V)
+            compopt -o nospace
+            ;;
+        esac
+      fi
+      return
+    fi
+
+    compopt -o default -o bashdefault
+  } \
+    && complete -F _comp_nvim nvim
+fi
+
+# aliases are not expanded by default during completion.
+for cmd in vi vim; do
+  [[ "$(alias $cmd 2> /dev/null)" == "alias $cmd='nvim'" ]] \
+    && type -f _comp_nvim > /dev/null 2>&1 \
+    && ! complete -p $cmd > /dev/null 2>&1 \
+    && complete -F _comp_nvim $cmd
+done