Final: RFC0062 - Predictive IntelliSense (#289)

* updated pr predictive intellisense

* Update 1-Draft/RFC00XX-PredIctive-IntelliSense.md

Co-authored-by: James Truher [MSFT] <[email protected]>

* updated pr predictive intellisense

* updated pr predictive intellisense

* removed reference to plugin as PSRL option

* changed providers to plugins and cleanup

* Corrections

* Merge RFC0062 - Predictive IntelliSense as Final

Co-authored-by: James Truher [MSFT] <[email protected]>
Co-authored-by: Joey Aiello <[email protected]>

Author: 3 people

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+---
+RFC: RFC0062
+Author: Jason Helmick
+Status: Final
+Area: Shell
+Comments Due: 10/31/2020
+---
+
+# Motivation
+
+Tab completion has accelerated the success of both new and experienced PowerShell users. New users
+get the benefit of discovery; seeing available cmdlets and parameters as options while interactively
+typing. Experienced users receive the benefit of acceleration; typing less while using the **<tab>**
+key to quickly complete a command.
+
+The increasing amount of technology translates to an increase in cmdlets and full command
+complexity. Predictive IntelliSense is an addition to the concept of Tab Completion to assist the
+user in successfully completing full commands.
+
+## Predictive IntelliSense
+
+The prediction suggestion appears as colored text following the user’s cursor. This enables new and
+experienced users of PowerShell to discover, edit, and execute full commands based on matching
+predictions from the user’s history or additional plugins.
+
+Additional plugins enhance historic predictions by providing domain specific commands and task
+completions. Predictive IntelliSense includes an extension model to support the registration of
+additional plugins.
+
+Predictions may be displayed in either **InlineView** or **ListView** depending on the user’s
+preference. Below, predictions are displayed with InlineView.
+
+![image](./media/pred-wlc.png)
+
+Below, predictions are displayed with a dropdown in ListView.
+
+![image](./media/pred-listview.png)
+
+## Release plan
+
+Similar to tab completion, Predictive IntelliSense is implemented in both the PowerShell engine and
+presented through the PSReadLine module. In an effort to support the most PowerShell users, the
+presentation of history-based predictions will be available to the following versions:
+
+- Windows Powershell 5.1
+- PowerShell 7.0+
+
+Additional plugins require the the extension framework implemented in the PowerShell engine. Support
+for additional plugins is available in the following versions:
+
+- PowerShell 7.2+
+
+History-based predictions initial preview and ship plan:
+
+- PSReadLine 2.1.0-beta2 currently available for download from PSGallery
+- PSReadLine 2.1.0-GA will ship with PowerShell 7.1
+- PSReadLine 2.1.0-GA will be available for download from PSGallery
+- History based prediction in the **InlineView**
+
+Extension/Plugin support initial preview and ship plan:
+
+- PSReadLine 2.2.0-beta1 planned availability in October 20
+- PSReadline 2.2.0-beta3 planned availability in June 21
+- PSReadLine 2.2.0-GA will ship with PowerShell 7.2
+- PSReadLine 2.2.0-GA will be available for download from PSGallery
+- Includes support for **InlineView** and **ListView**
+- Includes support for additional prediction source **HistoryAndPlugins**
+- Note: Windows PowerShell 5.1 and PowerShell 7.0 will only support prediction source **History**.
+  PowerShell 7.2+ will support prediction sources **History** and **HistoryAndPlugins**
+
+## Goals/Non-Goals
+
+ Goals:
+
+- Provide suggestions from PSReadLine history
+- The user will be able to enable and disable Predictive IntelliSense
+- The user will be able to change between InlineView and ListView
+- The user will have keyboard shortcuts to navigate and edit a prediction
+- The user will be able to register additional plugins when desired
+- The user may customize the color of a prediction to support accessibility needs
+
+Non-goals:
+
+- The extension framework doesn't allow a plugin implementation to call into the Runspace where
+  PSReadLine is running when providing predictive suggestions.
+- VSCode implementation. We agree this is important for a consistent experience and are working to
+  bring this feature in a future release, but the user experience for VS Code is outside the scope of this RFC.
+
+## Specification
+
+The proposal is to add Predictive IntelliSense and an extension model to improve the user
+interactive experience.
+
+### Key Design Considerations Predictive IntelliSense
+
+Predictive IntelliSense displays the most likely match from command history. The prediction may
+change if a better match is found as the user types additional information. The predicted command
+may be accepted, edited, or ignored.
+
+![Prediction - Historical](./media/pred-wlc.png)
+
+### Install and Remove Predictive IntelliSense
+
+Predictive IntelliSense application programming interface (API) is implemented in the PowerShell
+engine and presented through the PSReadLine module. To receive the benefits of Predictive
+IntelliSense based on your PowerShell version, download and install the PSReadLine module from
+PSGallery
+
+The current release is PSReadLine 2.1.0 Beta 2:
+
+```powershell
+Install-Module PSReadLine -RequiredVersion 2.1.0-beta2 -AllowPrerelease
+```
+
+It is possible to unload or uninstall the PSReadLine module to disable Predictive IntelliSense. This
+creates a negative impact to customers as it would remove all features of PSReadLine. For this
+reason, Predictive IntelliSense has its own PSReadLine configuration to enable and disable
+predictions.
+
+Note - When upgrading PowerShell preview versions, it's important to upgrade to the corresponding
+version of PSReadLine. Some beta versions may result in an error when PowerShell starts.
+
+### Enabling and Disabling Predictions
+
+By default, the feature Predictive IntelliSense is disabled. The impact of enabling this feature by
+default may cause new and existing users to become confused at the shell prompt. The feature is
+enabled and disabled with a PSReadLine command Set-PSReadLineOption that is executed at the shell
+prompt or in the user's Profile.
+
+Predictive IntelliSense in PSReadLine 2.1.0-beta2 currently supports the following arguments for
+prediction source;
+
+- None - This option disables Predictive IntelliSense
+- History - This option uses only the PSReadLine history for predictions
+
+Starting with PSReadLine 2.2.0-beta1, Predictive IntelliSense will support the following arguments
+for prediction source;
+
+- None - This option disables Predictive IntelliSense
+- History - This option uses only the PSReadLine history for predictions
+- HistoryAndPlugins - History provides initial completions, plugins provide additional completions.
+
+To enable Predictive IntelliSense, enter the following command in the shell or in the users Profile:
+
+```powershell
+Set-PSReadLineOption -PredictionSource History
+```
+
+To disable Predictive IntelliSense, enter the following command in the shell or in the users Profile:
+
+```powershell
+Set-PSReadLineOption -PredictionSource None
+```
+
+### Changing the Prediction View
+
+Beginning with 2.2.0-beta1, Predictions are displayed in one of two views depending on the user
+preference. The default view is InlineView.
+
+- InlineView – This is the default view and displays the prediction inline with the user’s typing.
+  This view is similar to other shells Fish and ZSH.
+- ListView – ListView provides a dropdown list of predictions below the line the user is typing.
+  Users may quickly scan the list, highlight and select the desired prediction.
+
+Users may change the view at the command line using the keybinding F2 or `Set-PSReadLineOption`. The
+`Set-PSReadLineOption` may be stored in the user's profile.
+
+```powershell
+Set-PSReadLineOption -PredictionViewStyle ListView
+```
+
+### Change the Prediction Color for Accessibility
+
+By default, predictions appear on the same line the user is typing in a different customizable
+color. To support accessibility needs, the prediction color is settable in the shell or user's
+profile.
+
+The default light-grey prediction text color;
+
+```powershell
+Set-PSReadLineOption -Colors @{ InLinePrediction = "`e[38;5;238m"}
+```
+
+Starting with PSReadLine 2.1.0-RC1, `Set-PSReadLineOption -Colors` array will include
+**InLinePrediction** to set the color of predictive text for **InLineView**.
+
+Beginning with PSReadLine 2.2.0-beta1, `Set-PSReadLineOption -Colors` array will include;
+
+- **ListPredictionColor** to set color for '>' and source names in **ListView**
+- **ListPredictionSelectionColor** to set color for the highlighted selection in **ListView**
+
+Examples of user changing prediction color:
+
+![pi-color](./media/pi-color.png)
+![pi-color](./media/pi-color2.png)
+![pi-color](./media/pi-color3-background.png)
+
+```powershell
+Set-PSReadLineOption -Colors @{ InLinePrediction = '#8A0303'}
+Set-PSReadLineOption -Colors @{ InLinePrediction = '#2F7004'}
+Set-PSReadLineOption -Colors @{ InLinePrediction = "`e[36;7;238m"}
+```
+
+Multiple types of color code values are supported in PSReadLine. For more information see
+Set-PSReadLineOption in
+[PSReadLine](https://docs.microsoft.com/en-us/powershell/module/PSReadline/Set-PSReadlineOption?view=powershell-7)
+
+Examples of different color code values:
+
+```powershell
+ # Use a ConsoleColor enum
+Set-PSReadLineOption -Colors @{ InLinePrediction = 'DarkRed'}
+Set-PSReadLineOption -Colors @{ InLinePrediction = [ConsoleColor]::DarkRed}
+
+ # 24 bit color escape sequence on supported terminals
+Set-PSReadLineOption -Colors @{ InLinePrediction = "`e[38;5;100m"}
+
+ # RGB value
+Set-PSReadLineOption -Colors @{ InLinePrediction = "#8181f7"}
+```
+
+### Key Bindings for Predictions
+
+Key bindings control cursor movement and additional features within the prediction. To support users
+running Predictive IntelliSense on multiple platforms, key bindings are user-settable in the shell
+and a user’s PowerShell profile.
+
+Example of setting a key binding in the shell or user’s profile:
+
+```powershell
+Set-PSReadLineOption -HistorySearchCursorMovesToEnd
+Set-PSReadLineKeyHandler -Key UpArrow -Function HistorySearchBackward
+Set-PSReadLineKeyHandler -Key DownArrow -Function HistorySearchForward
+```
+
+List of suggested key bindings defined in **SamplePSReadLineProfile.ps1**
+
+Key Binding   | PSReadLine Function    | Description
+------------- | -------------------    | -----------
+Up Arrow	    | HistorySearchBackward  | Move backward through history
+Down Arrow	  | HistorySearchForward	 | Move forward through history
+F7	          | Profile Code	         | Opens Out-GridView with full history
+F1	          | Profile Code	         | Opens the Help window for the current command or parameter
+F2            | Profile Code           | Switches between InLineView and ListView
+Ctrl-b	      | Profile Code	         | Add command to history
+Ctrl-q	      | TabCompleteNext	       | Windows style Tab for Emacs mode
+Ctrl-Q	      | TabCompletePrevious	   | Windows style Tab for Emacs mode
+Ctrl-c	      | Copy	                 | Clipboard interaction for Emacs mode
+Ctrl-v	      | Paste	                 | Clipboard interaction for Emacs mode
+Ctrl-d,Ctrl-c | CaptureScreen	         | Captures screen for pasting to email or blog
+Alt-d	        | ShellKillWord	         | Token based movement bound to Emacs word movement
+Alt-Backspace | ShellBackwardKillWord  | “
+Alt-b	        | ShellBackwardWord	     | “
+Alt-f	        | ShellForwardWord	     | “
+Alt-B	        | SelectShellBackwardWord| “
+Alt-F	        | SelectShellForwardWord | “
+“ or ‘	      | Profile Code	         | Insert Smart quotes
+( or { or [	  | Profile Code	         | Insert matching braces
+Backspace	    | Profile Code    	     | Delete previous character
+Alt-w	        | Profile Code	         | Save current line in history – don’t execute
+Ctrl-V	      | Profile Code    	     | Paste clipboard as a Here string
+Alt-(	        | Profile Code	         | Insert parenthesis around selection or entire line
+Alt-‘	        | Profile Code	         | Toggle quotes on argument under cursor
+Alt-%	        | Profile Code	         | Replace aliases with resolved commands
+
+### Search history based on cursor location
+
+The history from PSReadLine is searchable when the user begins typing into the shell.
+Users may search the entire prediction history for commands matching under the current cursor
+position. Users may search history based on 'Verb', 'Noun' and 'Parameter' of a cmdlet
+using the up/down arrow keys.
+
+- Searching history from cmdlet verb.
+![Verb](./media/pi-arrow-verb.gif)
+
+- Searching history from cmdlet noun.
+![noun](./media/pi-arrow-noun.gif)
+
+- Searching history from parameter.
+![Param](./media/pi-arrow-param.gif)
+
+### Edit predictions before accepting the prediction
+
+Users may navigate prediction tokens to make changes to parameters, arguments, and additional
+pipeline commands. The prediction model will update the displayed prediction from the closest
+matches in PSReadLine history or added provider.
+
+In the example below, a user navigates the prediction, pausing to change the -Property argument and
+receiving an updated prediction.
+
+![arg change](./media/pi-fb.gif)
+
+## Prediction Extension Model
+
+Additional plugins enhance historic predictions by providing domain specific commands and task
+completions. Plugins register with the PowerShell engine which includes an extension model
+to support the registration.
+
+An RFC for this subsystem will be coming in the future. For more information about the extension
+model, see
+[Initial work of the subsystem plugin model](https://github.com/PowerShell/PowerShell/pull/13186)
+
+## Extension Model Goals/Non-Goals
+
+ Goals:
+
+- Provide extension model to support additional plugins
+- Support the discovery of plugins using `Get-PSSubsystem`
+- Provide Module owners method of registration
+- Provide improvements to the predictors through feedback
+
+Non-goals:
+
+- Register/Unregister-Subsystem cmdlets are not planned because it's targeting binary subsystem
+  implementations, which should deal with registration/unregistration via APIs.
+- Server-side provider privacy is the responsibility of the provider module
+
+## Extension Model Specification
+
+### Discovery of Provider Metadata and Registration
+
+Plugins are registered automatically to the PowerShell engine when the user installs a provider
+module. Removal of registration occurs when the module is removed.
+
+Starting with PowerShell 7.1 Preview 7, and as an experimental feature of PowerShell 7.1-RC.1, the
+`Get-PSSubsystem` cmdlet is an experimental feature of the `PSSubsystemPluginModel`. To enable the
+experimental feature:
+
+```powershell
+Enable-ExperimentalFeature -Name PSSubsystemPluginModel
+```
+
+To list the currently installed plugins and their respective metadata such as version information:
+
+```powershell
+Get-PSSubSystem -Kind CommandPredictor
+```
+
+Example output with no additional plugins registered;
+
+```output
+Kind              SubsystemType   IsRegistered Implementations
+----              -------------   ------------ ---------------
+CommandPredictor  ICommandPredic…        False {}
+```
+
+Example output with an additional provider registered;
+
+```output
+Kind              SubsystemType   IsRegistered Implementations
+----              -------------   ------------ ---------------
+CommandPredictor  ICommandPredic…         True {Az Predictor}
+```