Add --variables subcommand that prints variable names (#608)

Add a subcommand that prints out a space-separated list of the names of
top-level variables in the justfile.

The syntax is:

    $ just --variables
    a b c

This can be used for any purpose, but is mostly intended for completion
scripts, so that they can get the names of variables without using
`--evaluate`.

Additionally:

- Add `bin/generate-completions` script to regenerate checked-in
  completions
- Update dependencies
- Regenerate checked-in completions

completions/just.bash

@@ -20,7 +20,7 @@ _just() {
 
     case "${cmd}" in
         just)
-            opts=" -q -v -e -l -h -V -f -d -s  --dry-run --highlight --no-highlight --quiet --clear-shell-args --verbose --dump --edit --evaluate --init --list --summary --help --version --color --justfile --set --shell --shell-arg --working-directory --completions --show  <ARGUMENTS>... "
+            opts=" -q -v -e -l -h -V -f -d -s  --dry-run --highlight --no-highlight --quiet --clear-shell-args --verbose --dump --edit --evaluate --init --list --summary --variables --help --version --color --justfile --set --shell --shell-arg --working-directory --completions --show  <ARGUMENTS>... "
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 1 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0

completions/just.elvish

@@ -42,6 +42,7 @@ edit:completion:arg-completer[just] = [@words]{
             cand -l 'List available recipes and their arguments'
             cand --list 'List available recipes and their arguments'
             cand --summary 'List names of available recipes'
+            cand --variables 'List names of variables'
             cand -h 'Print help information'
             cand --help 'Print help information'
             cand -V 'Print version information'

completions/just.fish

@@ -18,5 +18,6 @@ complete -c just -n "__fish_use_subcommand" -l evaluate -d 'Print evaluated vari
 complete -c just -n "__fish_use_subcommand" -l init -d 'Initialize new justfile in project root'
 complete -c just -n "__fish_use_subcommand" -s l -l list -d 'List available recipes and their arguments'
 complete -c just -n "__fish_use_subcommand" -l summary -d 'List names of available recipes'
+complete -c just -n "__fish_use_subcommand" -l variables -d 'List names of variables'
 complete -c just -n "__fish_use_subcommand" -s h -l help -d 'Print help information'
 complete -c just -n "__fish_use_subcommand" -s V -l version -d 'Print version information'

completions/just.powershell

@@ -47,6 +47,7 @@ Register-ArgumentCompleter -Native -CommandName 'just' -ScriptBlock {
             [CompletionResult]::new('-l', 'l', [CompletionResultType]::ParameterName, 'List available recipes and their arguments')
             [CompletionResult]::new('--list', 'list', [CompletionResultType]::ParameterName, 'List available recipes and their arguments')
             [CompletionResult]::new('--summary', 'summary', [CompletionResultType]::ParameterName, 'List names of available recipes')
+            [CompletionResult]::new('--variables', 'variables', [CompletionResultType]::ParameterName, 'List names of variables')
             [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
             [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
             [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Print version information')

completions/just.zsh

@@ -42,6 +42,7 @@ _just() {
 '-l[List available recipes and their arguments]' \
 '--list[List available recipes and their arguments]' \
 '--summary[List names of available recipes]' \
+'--variables[List names of variables]' \
 '-h[Print help information]' \
 '--help[Print help information]' \
 '-V[Print version information]' \