Switch to Register-ArgumentCompleter for tab expansion

[cspotcode]

I saw talk of switching to the more modern Register-ArgumentCompleter for tab completion. This is the most minimal implementation of such a switch. Completion logic is the same. We register ourselves as a -Native completer for git, gitk, and tgit. When invoked, we convert the command AST into a string, trim it to match what the old completion logic is expecting, and pass it along.

[rkeithhill]

Does this actually work on Windows PowerShell? My experience with the built-in Register-ArgumentCompleter in Windows PowerShell 5.1 is that it won't auto-complete native parameters that start with - or --. This would be a serious problem for Git.

[cspotcode]

Whoops, you're correct, it does not work. :( I'll post context.

[dahlbyk]

So it sounds like we want to use Register-ArgumentCompleter on PS 6+, and fall back on the previous behavior for PS 5.1?

[cspotcode]

I didn't realize the built-in Register-ArgumentCompleter on Windows PowerShell has a bug where it doesn't tab-complete arguments that begin with a hyphen.

MicrosoftDocs/PowerShell-Docs#1979
PowerShell/PowerShell#2912

So I guess this is only useful if you want posh-git to get the benefits of built-in Register-ArgumentCompleter on new-enough versions of Powershell and fallback to the old logic on e.g. Windows PowerShell. The benefits of built-in Register-ArgumentCompleter are that you can tab complete e.g. after the "b" in this example:

echo $branches | ? { git b<# <-- cursor here #> } | Out-Null

[rkeithhill]

I've been looking at this. I think the following could work:

if ($PSVersionTable.PSVersion.Major -ge 6) {
    Register-ArgumentCompleter -CommandName git,tgit,gitk -Native -ScriptBlock {
        param($wordToComplete, $commandAst, $cursorPosition)

        Expand-GitCommand $commandAst.Extent.Text
    }
}
else {
    $PowerTab_RegisterTabExpansion = if (Get-Module -Name powertab) { Get-Command Register-TabExpansion -Module powertab -ErrorAction SilentlyContinue }
    if ($PowerTab_RegisterTabExpansion) {
        & $PowerTab_RegisterTabExpansion "git.exe" -Type Command {
            param($Context, [ref]$TabExpansionHasOutput, [ref]$QuoteSpaces)  # 1:

            $line = $Context.Line
            $lastBlock = [regex]::Split($line, '[|;]')[-1].TrimStart()
            $TabExpansionHasOutput.Value = $true
            Expand-GitCommand $lastBlock
        }
        return
    }

    if (Test-Path Function:\TabExpansion) {
        Rename-Item Function:\TabExpansion TabExpansionBackup
    }

    function TabExpansion($line, $lastWord) {
        $lastBlock = [regex]::Split($line, '[|;]')[-1].TrimStart()

        switch -regex ($lastBlock) {
            # Execute git tab completion for all git-related commands
            "^$(Get-AliasPattern git) (.*)" { Expand-GitCommand $lastBlock }
            "^$(Get-AliasPattern tgit) (.*)" { Expand-GitCommand $lastBlock }
            "^$(Get-AliasPattern gitk) (.*)" { Expand-GitCommand $lastBlock }

            # Fall back on existing tab expansion
            default {
                if (Test-Path Function:\TabExpansionBackup) {
                    TabExpansionBackup $line $lastWord
                }
            }
        }
    }
}

If you'd like to make this change, then I will accept and merge it. Also, in looking at the completer impl, I wasn't sure why we needed the padding/substring calls. Register-ArgumentCompleter seems to do a pretty good job of supplying just the command up to the param to complete in $commandAst.Extent.Text.

If you don't have time for this, I can submit a PR to do the above but I'll make sure you get credit for this in the changelog.

@dahlbyk I think it would be good to do one more beta drop with this change.

[rkeithhill]

Close in favor of #711 @cspotcode I'll make sure you get the credit for this in the changelog. Thanks for investigating this and doing the work!!