watchexec/completions/powershell

using namespace System.Management.Automation
using namespace System.Management.Automation.Language

Register-ArgumentCompleter -Native -CommandName 'watchexec' -ScriptBlock {
    param($wordToComplete, $commandAst, $cursorPosition)

    $commandElements = $commandAst.CommandElements
    $command = @(
        'watchexec'
        for ($i = 1; $i -lt $commandElements.Count; $i++) {
            $element = $commandElements[$i]
            if ($element -isnot [StringConstantExpressionAst] -or
                $element.StringConstantType -ne [StringConstantType]::BareWord -or
                $element.Value.StartsWith('-') -or
                $element.Value -eq $wordToComplete) {
                break
        }
        $element.Value
    }) -join ';'

    $completions = @(switch ($command) {
        'watchexec' {
            [CompletionResult]::new('-w', '-w', [CompletionResultType]::ParameterName, 'Watch a specific file or directory')
            [CompletionResult]::new('--watch', '--watch', [CompletionResultType]::ParameterName, 'Watch a specific file or directory')
            [CompletionResult]::new('-W', '-W ', [CompletionResultType]::ParameterName, 'Watch a specific directory, non-recursively')
            [CompletionResult]::new('--watch-non-recursive', '--watch-non-recursive', [CompletionResultType]::ParameterName, 'Watch a specific directory, non-recursively')
            [CompletionResult]::new('-F', '-F ', [CompletionResultType]::ParameterName, 'Watch files and directories from a file')
            [CompletionResult]::new('--watch-file', '--watch-file', [CompletionResultType]::ParameterName, 'Watch files and directories from a file')
            [CompletionResult]::new('-c', '-c', [CompletionResultType]::ParameterName, 'Clear screen before running command')
            [CompletionResult]::new('--clear', '--clear', [CompletionResultType]::ParameterName, 'Clear screen before running command')
            [CompletionResult]::new('-o', '-o', [CompletionResultType]::ParameterName, 'What to do when receiving events while the command is running')
            [CompletionResult]::new('--on-busy-update', '--on-busy-update', [CompletionResultType]::ParameterName, 'What to do when receiving events while the command is running')
            [CompletionResult]::new('-s', '-s', [CompletionResultType]::ParameterName, 'Send a signal to the process when it''s still running')
            [CompletionResult]::new('--signal', '--signal', [CompletionResultType]::ParameterName, 'Send a signal to the process when it''s still running')
            [CompletionResult]::new('--stop-signal', '--stop-signal', [CompletionResultType]::ParameterName, 'Signal to send to stop the command')
            [CompletionResult]::new('--stop-timeout', '--stop-timeout', [CompletionResultType]::ParameterName, 'Time to wait for the command to exit gracefully')
            [CompletionResult]::new('--map-signal', '--map-signal', [CompletionResultType]::ParameterName, 'Translate signals from the OS to signals to send to the command')
            [CompletionResult]::new('-d', '-d', [CompletionResultType]::ParameterName, 'Time to wait for new events before taking action')
            [CompletionResult]::new('--debounce', '--debounce', [CompletionResultType]::ParameterName, 'Time to wait for new events before taking action')
            [CompletionResult]::new('--delay-run', '--delay-run', [CompletionResultType]::ParameterName, 'Sleep before running the command')
            [CompletionResult]::new('--poll', '--poll', [CompletionResultType]::ParameterName, 'Poll for filesystem changes')
            [CompletionResult]::new('--shell', '--shell', [CompletionResultType]::ParameterName, 'Use a different shell')
            [CompletionResult]::new('--emit-events-to', '--emit-events-to', [CompletionResultType]::ParameterName, 'Configure event emission')
            [CompletionResult]::new('-E', '-E ', [CompletionResultType]::ParameterName, 'Add env vars to the command')
            [CompletionResult]::new('--env', '--env', [CompletionResultType]::ParameterName, 'Add env vars to the command')
            [CompletionResult]::new('--wrap-process', '--wrap-process', [CompletionResultType]::ParameterName, 'Configure how the process is wrapped')
            [CompletionResult]::new('--color', '--color', [CompletionResultType]::ParameterName, 'When to use terminal colours')
            [CompletionResult]::new('--project-origin', '--project-origin', [CompletionResultType]::ParameterName, 'Set the project origin')
            [CompletionResult]::new('--workdir', '--workdir', [CompletionResultType]::ParameterName, 'Set the working directory')
            [CompletionResult]::new('-e', '-e', [CompletionResultType]::ParameterName, 'Filename extensions to filter to')
            [CompletionResult]::new('--exts', '--exts', [CompletionResultType]::ParameterName, 'Filename extensions to filter to')
            [CompletionResult]::new('-f', '-f', [CompletionResultType]::ParameterName, 'Filename patterns to filter to')
            [CompletionResult]::new('--filter', '--filter', [CompletionResultType]::ParameterName, 'Filename patterns to filter to')
            [CompletionResult]::new('--filter-file', '--filter-file', [CompletionResultType]::ParameterName, 'Files to load filters from')
            [CompletionResult]::new('-j', '-j', [CompletionResultType]::ParameterName, '[experimental] Filter programs')
            [CompletionResult]::new('--filter-prog', '--filter-prog', [CompletionResultType]::ParameterName, '[experimental] Filter programs')
            [CompletionResult]::new('-i', '-i', [CompletionResultType]::ParameterName, 'Filename patterns to filter out')
            [CompletionResult]::new('--ignore', '--ignore', [CompletionResultType]::ParameterName, 'Filename patterns to filter out')
            [CompletionResult]::new('--ignore-file', '--ignore-file', [CompletionResultType]::ParameterName, 'Files to load ignores from')
            [CompletionResult]::new('--fs-events', '--fs-events', [CompletionResultType]::ParameterName, 'Filesystem events to filter to')
            [CompletionResult]::new('--completions', '--completions', [CompletionResultType]::ParameterName, 'Generate a shell completions script')
            [CompletionResult]::new('--log-file', '--log-file', [CompletionResultType]::ParameterName, 'Write diagnostic logs to a file')
            [CompletionResult]::new('-r', '-r', [CompletionResultType]::ParameterName, 'Restart the process if it''s still running')
            [CompletionResult]::new('--restart', '--restart', [CompletionResultType]::ParameterName, 'Restart the process if it''s still running')
            [CompletionResult]::new('--stdin-quit', '--stdin-quit', [CompletionResultType]::ParameterName, 'Exit when stdin closes')
            [CompletionResult]::new('--no-vcs-ignore', '--no-vcs-ignore', [CompletionResultType]::ParameterName, 'Don''t load gitignores')
            [CompletionResult]::new('--no-project-ignore', '--no-project-ignore', [CompletionResultType]::ParameterName, 'Don''t load project-local ignores')
            [CompletionResult]::new('--no-global-ignore', '--no-global-ignore', [CompletionResultType]::ParameterName, 'Don''t load global ignores')
            [CompletionResult]::new('--no-default-ignore', '--no-default-ignore', [CompletionResultType]::ParameterName, 'Don''t use internal default ignores')
            [CompletionResult]::new('--no-discover-ignore', '--no-discover-ignore', [CompletionResultType]::ParameterName, 'Don''t discover ignore files at all')
            [CompletionResult]::new('--ignore-nothing', '--ignore-nothing', [CompletionResultType]::ParameterName, 'Don''t ignore anything at all')
            [CompletionResult]::new('-p', '-p', [CompletionResultType]::ParameterName, 'Wait until first change before running command')
            [CompletionResult]::new('--postpone', '--postpone', [CompletionResultType]::ParameterName, 'Wait until first change before running command')
            [CompletionResult]::new('-n', '-n', [CompletionResultType]::ParameterName, 'Shorthand for ''--shell=none''')
            [CompletionResult]::new('--no-environment', '--no-environment', [CompletionResultType]::ParameterName, 'Deprecated shorthand for ''--emit-events=none''')
            [CompletionResult]::new('--only-emit-events', '--only-emit-events', [CompletionResultType]::ParameterName, 'Only emit events to stdout, run no commands')
            [CompletionResult]::new('--no-process-group', '--no-process-group', [CompletionResultType]::ParameterName, 'Don''t use a process group')
            [CompletionResult]::new('-1', '-1', [CompletionResultType]::ParameterName, 'Testing only: exit Watchexec after the first run')
            [CompletionResult]::new('-N', '-N ', [CompletionResultType]::ParameterName, 'Alert when commands start and end')
            [CompletionResult]::new('--notify', '--notify', [CompletionResultType]::ParameterName, 'Alert when commands start and end')
            [CompletionResult]::new('--timings', '--timings', [CompletionResultType]::ParameterName, 'Print how long the command took to run')
            [CompletionResult]::new('-q', '-q', [CompletionResultType]::ParameterName, 'Don''t print starting and stopping messages')
            [CompletionResult]::new('--quiet', '--quiet', [CompletionResultType]::ParameterName, 'Don''t print starting and stopping messages')
            [CompletionResult]::new('--bell', '--bell', [CompletionResultType]::ParameterName, 'Ring the terminal bell on command completion')
            [CompletionResult]::new('--no-meta', '--no-meta', [CompletionResultType]::ParameterName, 'Don''t emit fs events for metadata changes')
            [CompletionResult]::new('--print-events', '--print-events', [CompletionResultType]::ParameterName, 'Print events that trigger actions')
            [CompletionResult]::new('--manual', '--manual', [CompletionResultType]::ParameterName, 'Show the manual page')
            [CompletionResult]::new('-v', '-v', [CompletionResultType]::ParameterName, 'Set diagnostic log level')
            [CompletionResult]::new('--verbose', '--verbose', [CompletionResultType]::ParameterName, 'Set diagnostic log level')
            [CompletionResult]::new('-h', '-h', [CompletionResultType]::ParameterName, 'Print help (see more with ''--help'')')
            [CompletionResult]::new('--help', '--help', [CompletionResultType]::ParameterName, 'Print help (see more with ''--help'')')
            [CompletionResult]::new('-V', '-V ', [CompletionResultType]::ParameterName, 'Print version')
            [CompletionResult]::new('--version', '--version', [CompletionResultType]::ParameterName, 'Print version')
            break
        }
    })

    $completions.Where{ $_.CompletionText -like "$wordToComplete*" } |
        Sort-Object -Property ListItemText
}