Suggestion: support inline previews of tab completions

[mklement0]

^{Note: The suggested feature may have to be constrained to certain types of completions, and it is debatable whether it should be the default behavior or opt-in via a new option, but overall I think it would greatly streamline the tab-completion experience.}

Imagine if PSReadLine showed you a preview of what the token you're currently typing would expand to if you pressed Tab at that moment; e.g.:

That is, having typed parameter-name prefix -Fo, PSReadLine would show you, via the differently colored - "rce" part, that if you pressed Tab at that moment you'd end up with -Force.

If the preview doesn't indicate the desired parameter, simply keep typing until the desired one is suggested; e.g., additionally type an l to make the preview show "lowSymlink" to inform you that pressing Tab then would complete to -FollowSymlink.

This makes for a very convenient experience if you know what exactly what completion you're looking for : just keep typing - without interruption - until you see what you want, then press Tab.

A challenge is how to handle transitioning to reviewing all possible completions at a given point, given that pressing Tab in this scenario would have to result in instant completion (whereas currently you can use it to cycle through the candidate completions).

• If technically feasible, pressing Tab right after a completion would still be aware of what prefix was actually typed and would still allow cycling through the possible completions.

• Alternatively / complementarily, a separate key chord such as Ctrl + Tabcould be used to show all possibly completions in a menu, via built-in function MenuComplete.

---

As an aside: If someone prefers the current tab-completion behavior in principle, but would like to show a menu of possible completions in case of ambiguity, they can add the following to your $PROFILE:

Set-PSReadlineKeyHandler -Key Tab -Function MenuComplete

Environment data

PS version: 6.1.0-preview.4
PSReadline version: 2.0.0-beta2
os: 10.0.16299.15 (WinBuild.160101.0800)
PS file version: 6.1.0

[felixfbecker]

Duplicate of #687

[mklement0]

Thanks, @felixfbecker - hadn't seen yours. Certainly closely related, but your suggestion is about completions from the history, whereas this one is about the standard, syntax-based tab completions.

Both behaviors are useful, but I'm unclear on if and how they could be rolled into a single feature: when would you choose which completion source?

[TBBle]

It appears that https://github.com/PowerShell/CompletionPredictor delivers this feature via Prediction. The default keys are different because it's Prediction (being fed from Completion) rather than Completion, but that does also resolve the question in #741 (comment), because you get suggestions from both history and plugins by default, and in the list view (but not inline, see #1945) it tells you where the prediction came from.

[daxian-dbw]

The ask of this issue can be achieved by using the CompletionPredictor module along with PSReadLine 2.2+. Especially, the predictive intellisense feature is enabled by default in v2.2.6 release of PSReadLine.

Here is a GIF to show the asked behavior (using Windows edit mode and HistoryAndPlugin as the PredictionSource):

Given this, I will mark the issue as fixed.

[TBBle]

The plugin https://github.com/PowerShell/CompletionPredictor adds (If I understand correctly) "syntax-based completions". In PSReadLine 2.2.6, Set-PSReadLineOption -PredictionSource HistoryAndPlugin is the default, so installing and importing that module should be sufficient to resolve this ticket.

(And I can see that's happening in parallel as I comment)

[mklement0]

One more thing, because it may not be obvious (should someone in the future stumble upon this thread): plugins (completer modules) must be imported explicitly into every session (via $PROFILE) - PSReadLine, at last as of v2.2.6, does not try to discover and load them automatically (for performance reasons, I presume).