[plug-in] Harden and polish the Plug-in System

[ashumilova]

The first implementation phase of Plug-in system has been finished, and it included all the essential APIs needed for the start to interact with Theia components from plug-ins.

Just to revise, they are the following: Preferences, Commands, Notifications, Editor, Status bar, Terminal, Open/Save/Input Dialogs and Output channel APIs. Also new namespace - environment was introduced.

The next step is to make our Plug-ins API model tougher and more clearly defined and used.

It could be divided in following sections, which could also be split in separate epics.

Fill-in the missing pieces:

There the APIs, that are still missing, and the list could really increase during work being in progress.
(Note: the order is not prioritized)

• Workspace Folder Pick API Introduce Workspace Folder Pick API #2337
• Tree + Tree view + Tree data provider [plug-in] Add Tree View and Tree Data Provider APIs #2782
• File system watcher creator (needed for LS)
• Find files
• Apply edit (workspace) (needed for LS) [plug-in] Add API to apply workspace edit #2784
• Configuration and Defaults contribution
• Languages [lsp][plug-in] Ease the integration of a new LSP into Eclipse Che with plug-ins eclipse-che/che#10206 [plug-in] Languages API #2341
• Debugger API (bigger)
• Extensions API [plug-in] Implement Plugin API #2561
• WebView API

Low priority:

• syntax highlight APIs
• Register task provider
• Register file system provider [plug-in] API for register a filesystem provider #2861
• Version control system management APIs

Nice to have

• Themes management
• Snippets
• Menu Plugin API [plug-in] Menu Plugin API  #2785
• Register text document content provider [plug-in] API for registering Text Document Content Provider  #2786
• Key bindings [plug-in] Keyboard Shortcuts Plugin API  #2783
• API endpoint for window.showTextDocument [plug-in] API endpoint for window.showTextDocument #2801
• API endpoint window.withProgress [plug-in] API endpoint for window.withProgress #2802

Plug-in Model documentation

• Provide the detailed documentation on all the existing APIs
• Provide the tutorial for plugin writers

Move existing extensions to plugin model

• SSH extension
• GitHub extension

[AlexTugarev]

can this be considered too? #2258

[ashumilova]

@AlexTugarev yes, sure

[vince-fugnitto]

I believe this issue is now outdated, and we can safely close. We have other "epics" which describe improvements to the plugin-system and vscode support.