Fix #5380: Add documentation for worksheet mode

Author: Duhemm

docs/docs/usage/ide-support.md

@@ -34,14 +34,15 @@ Status
 - Type information on hover
 - Go to definition (in the current project)
 - Find all references
+- Documentation on hover
+- [Worksheet mode](worksheet-mode.html)
 
 ## Partially working features:
 - Completion
 - Renaming
 - Go to definition in external projects
 
 ## Unimplemented features:
-- Documentation on hover
 - Formatting code (requires integrating with scalafmt)
 - Quick fixes (probably by integrating with scalafix)
 

docs/docs/usage/worksheet-mode.md

@@ -0,0 +1,116 @@
+---
+layout: doc-page
+title: "Worksheet mode with Dotty IDE"
+---
+
+A worksheet is a Scala file that is evaluated on save, and the result of each
+expression is shown in a column to the right of your program. Worksheets are
+like a REPL session on steroids, and enjoy 1st class editor support: completion,
+hyperlinking, interactive errors-as-you-type, etc. Worksheet use the extension
+`.sc`.
+
+How to use the worksheets
+=========================
+The only supported client for the Worksheet mode is [Visual Studio
+Code](https://code.visualstudio.com/).
+
+To use the worksheets, start Dotty IDE by [following the
+instruction]("./ide-support.html") and create a new file `MyWorksheet.sc` and
+write some code:
+
+```scala
+val xyz = 123
+println("Hello, worksheets!")
+456 + xyz
+```
+
+On top of the buffer, the message `Run this worksheet` appears. Click it to
+evaluate the code of the worksheet. Each line of output is printed on the right
+of the expression that produced it. The worksheets run with the classes of your
+project and its dependencies on their classpath.
+
+![](../../images/worksheets/worksheet-run.png "Run worksheet")
+
+Note that the worksheet are fully integrated with the rest of Dotty IDE: While
+typing, errors are shown, completions are suggested, and you can use all the
+other features of Dotty IDE such as go to definition, find all references, etc.
+
+![](../../images/worksheets/worksheet-help.png "IDE features in the worksheet")
+
+Implementation details
+======================
+
+In overview, the worksheets extend the Language Server Protocol and rely on the
+Dotty REPL to evaluate code.
+
+## Evaluation
+Each of the individual expressions and statements of the worksheet is extracted
+and passed to the Dotty REPL. After the REPL has finished evaluating one unit of
+input, it emits a special delimiter that indicates the end of the output for
+this input. (See `dotty.tools.languageserver.worksheet.InputStreamConsumer`)
+
+This process continues until all input has been evaluated.
+
+The Dotty REPL is run in a separate JVM. The `Evaluator` (see
+`dotty.tools.languageserver.worksheet.Evaluator`) will re-use a JVM if the
+configuration of the project hasn't changed.
+
+## Communication with the client
+The worksheets extend the Language Server Protocol and add one request and one
+notification.
+
+### Run worksheet request
+The worksheet run request is sent from the client to the server to request that
+the server runs a given worksheet and streams the result.
+
+*Request:*
+
+ - method: `worksheet/run`
+ - params: `WorksheetRunParams` defined as follows:
+   ```typescript
+   interface WorksheetRunParams {
+       /**
+        * The worksheet to evaluate.
+        */
+       textDocument: VersionedTextDocumentIdentifier;
+   }
+   ```
+
+*Response:*
+
+ - result: `WorksheetRunResult` defined as follows:
+   ```typescript
+   interface WorksheetRunResult {
+       /**
+        * Indicates whether evaluation was successful.
+        */
+       success: boolean;
+   }
+   ```
+
+### Worksheet output notification
+The worksheet output notification is sent from the server to the client to
+indicate that worksheet execution has produced some output.
+
+*Notification:*
+
+ - method: `worksheet/publishOutput`
+ - params: `WorksheetRunOutput` defined as follows:
+   ```typescript
+   interface WorksheetRunOutput {
+       /**
+        * The worksheet that produced this output.
+        */
+       textDocument: VersionedTextDocumentIdentifier;
+   
+       /**
+        * The line number of the expression that produced this output.
+        */
+       line: int;
+   
+       /**
+        * The output that has been produced.
+        */
+       content: string;
+   }
+   ```

docs/images/worksheets/worksheet-help.png

@@ -9,6 +9,8 @@ sidebar:
           url: docs/usage/sbt-projects.html
         - title: IDE support for Dotty
           url: docs/usage/ide-support.html
+        - title: Worksheet mode in Dotty IDE
+          url: docs/usage/worksheet-mode.html
         - title: cbt-projects
           url: docs/usage/cbt-projects.html
         - title: Dottydoc