Fix race condition in worksheet output

Sometimes, the `ApplyEdits` that we use in the worksheet to insert blank
lines so that the worksheet output fits were reordered. The lead to some
output of the worksheet being lost, with decorations being inserted
after the end of the file.

We know keep track of the edits that we want to apply to the worksheet
and ensure that they are executed in the same order as the messages were
received.

Author: Duhemm

vscode-dotty/src/worksheet.ts

@@ -63,6 +63,14 @@ class Worksheet implements Disposable {
    */
   private canceller?: CancellationTokenSource = undefined
 
+  /**
+   * The edits that should be applied to this worksheet.
+   *
+   * This is used to ensure that the blank lines added to fit the output of the worksheet
+   * are inserted in the same order as the output arrived.
+   */
+  private applyEdits: Promise<void> = Promise.resolve()
+
   constructor(readonly document: vscode.TextDocument, readonly client: BaseLanguageClient) {
   }
 
@@ -73,7 +81,7 @@ class Worksheet implements Disposable {
       this.canceller = undefined
     }
     this._onDidStateChange.dispose()
-	}
+  }
 
   /** Remove all decorations, and resets this worksheet. */
   private reset(): void {
@@ -83,6 +91,7 @@ class Worksheet implements Disposable {
     this.decoratedLines.clear()
     this.runVersion = -1
     this.margin = this.longestLine() + 5
+    this.applyEdits = Promise.resolve()
   }
 
   /**
@@ -111,6 +120,13 @@ class Worksheet implements Disposable {
     return this.canceller != undefined
   }
 
+  /** Display the output in the worksheet's editor. */
+  handleMessage(output: WorksheetPublishOutputParams, editor: vscode.TextEditor) {
+    this.applyEdits = this.applyEdits.then(() => {
+      this.displayAndSaveResult(output.line - 1, output.content, editor)
+    })
+  }
+
   /**
    * Run the worksheet in `document`, if a previous run is in progress, it is
    * cancelled first.
@@ -160,10 +176,10 @@ class Worksheet implements Disposable {
    * @param runResult  The result itself.
    * @param worksheet  The worksheet that receives the result.
    * @param editor     The editor where to display the result.
-   * @return A `Thenable` that will insert necessary lines to fit the output
+   * @return A `Promise` that will insert necessary lines to fit the output
    *         and display the decorations upon completion.
    */
-  public displayAndSaveResult(lineNumber: number, runResult: string, editor: vscode.TextEditor) {
+  public async displayAndSaveResult(lineNumber: number, runResult: string, editor: vscode.TextEditor): Promise<void> {
     const resultLines = runResult.trim().split(/\r\n|\r|\n/g)
 
     // The line where the next decoration should be put.
@@ -183,21 +199,18 @@ class Worksheet implements Disposable {
       this.runVersion += 1
     }
 
-    return vscode.workspace.applyEdit(addNewLinesEdit).then(_ => {
-      for (let line of resultLines) {
-        const decorationPosition = new vscode.Position(actualLine, 0)
-        const decorationMargin = this.margin - editor.document.lineAt(actualLine).text.length
-        const decorationType = this.createDecoration(decorationMargin, line)
-        const decorationOptions = { range: new vscode.Range(decorationPosition, decorationPosition), hoverMessage: line }
-        const decoration = new Decoration(decorationType, decorationOptions)
-
-        this.decoratedLines.add(actualLine)
-        this.decorations.push(decoration)
-
-        editor.setDecorations(decorationType, [decorationOptions])
-        actualLine += 1
-      }
-    })
+    await vscode.workspace.applyEdit(addNewLinesEdit);
+    for (let line of resultLines) {
+      const decorationPosition = new vscode.Position(actualLine, 0);
+      const decorationMargin = this.margin - editor.document.lineAt(actualLine).text.length;
+      const decorationType = this.createDecoration(decorationMargin, line);
+      const decorationOptions = { range: new vscode.Range(decorationPosition, decorationPosition), hoverMessage: line };
+      const decoration = new Decoration(decorationType, decorationOptions);
+      this.decoratedLines.add(actualLine);
+      this.decorations.push(decoration);
+      editor.setDecorations(decorationType, [decorationOptions]);
+      actualLine += 1;
+    }
   }
 
   /**
@@ -409,7 +422,7 @@ export class WorksheetProvider implements Disposable {
    * Handle the result of running part of a worksheet.
    * This is called when we receive a `worksheet/publishOutput`.
    *
-   * @param message The result of running part of a worksheet.
+   * @param output The result of running part of a worksheet.
    */
   private handleMessage(output: WorksheetPublishOutputParams) {
     const editor = vscode.window.visibleTextEditors.find(e => {
@@ -420,7 +433,7 @@ export class WorksheetProvider implements Disposable {
     if (editor) {
       const worksheet = this.worksheetFor(editor.document)
       if (worksheet) {
-        worksheet.displayAndSaveResult(output.line - 1, output.content, editor)
+        worksheet.handleMessage(output, editor)
       }
     }
   }