Fix scrollback going missing when increase size on Windows

src/Terminal.ts

@@ -1469,6 +1469,10 @@ export class Terminal extends Disposable implements ITerminal, IDisposable, IInp
       this._charSizeService.measure();
     }
 
+    // Sync the scroll area to make sure scroll events don't fire and scroll the viewport to an
+    // invalid location
+    this.viewport.syncScrollArea(true);
+
     this.refresh(0, this.rows - 1);
     this._onResize.fire({ cols: x, rows: y });
   }

src/browser/Types.d.ts

@@ -35,7 +35,7 @@ export interface IPartialColorSet {
 
 export interface IViewport extends IDisposable {
   scrollBarWidth: number;
-  syncScrollArea(): void;
+  syncScrollArea(immediate?: boolean): void;
   getLinesScrolled(ev: WheelEvent): number;
   onWheel(ev: WheelEvent): boolean;
   onTouchStart(ev: TouchEvent): void;

src/browser/Viewport.ts

@@ -61,7 +61,14 @@ export class Viewport extends Disposable implements IViewport {
    * Refreshes row height, setting line-height, viewport height and scroll area height if
    * necessary.
    */
-  private _refresh(): void {
+  private _refresh(immediate: boolean): void {
+    if (immediate) {
+      this._innerRefresh();
+      if (this._refreshAnimationFrame !== null) {
+        cancelAnimationFrame(this._refreshAnimationFrame);
+      }
+      return;
+    }
     if (this._refreshAnimationFrame === null) {
       this._refreshAnimationFrame = requestAnimationFrame(() => this._innerRefresh());
     }
@@ -89,40 +96,39 @@ export class Viewport extends Disposable implements IViewport {
 
     this._refreshAnimationFrame = null;
   }
-
   /**
    * Updates dimensions and synchronizes the scroll area if necessary.
    */
-  public syncScrollArea(): void {
+  public syncScrollArea(immediate: boolean = false): void {
     // If buffer height changed
     if (this._lastRecordedBufferLength !== this._bufferService.buffer.lines.length) {
       this._lastRecordedBufferLength = this._bufferService.buffer.lines.length;
-      this._refresh();
+      this._refresh(immediate);
       return;
     }
 
     // If viewport height changed
     if (this._lastRecordedViewportHeight !== this._renderService.dimensions.canvasHeight) {
-      this._refresh();
+      this._refresh(immediate);
       return;
     }
 
     // If the buffer position doesn't match last scroll top
     const newScrollTop = this._bufferService.buffer.ydisp * this._currentRowHeight;
     if (this._lastScrollTop !== newScrollTop) {
-      this._refresh();
+      this._refresh(immediate);
       return;
     }
 
     // If element's scroll top changed, this can happen when hiding the element
     if (this._lastScrollTop !== this._viewportElement.scrollTop) {
-      this._refresh();
+      this._refresh(immediate);
       return;
     }
 
     // If row height changed
     if (this._renderService.dimensions.scaledCellHeight / window.devicePixelRatio !== this._currentRowHeight) {
-      this._refresh();
+      this._refresh(immediate);
       return;
     }
   }

src/common/buffer/Buffer.ts

@@ -167,19 +167,25 @@ export class Buffer implements IBuffer {
       if (this._rows < newRows) {
         for (let y = this._rows; y < newRows; y++) {
           if (this.lines.length < newRows + this.ybase) {
-            if (this.ybase > 0 && this.lines.length <= this.ybase + this.y + addToY + 1) {
-              // There is room above the buffer and there are no empty elements below the line,
-              // scroll up
-              this.ybase--;
-              addToY++;
-              if (this.ydisp > 0) {
-                // Viewport is at the top of the buffer, must increase downwards
-                this.ydisp--;
-              }
-            } else {
-              // Add a blank line if there is no buffer left at the top to scroll to, or if there
-              // are blank lines after the cursor
+            if (this._optionsService.options.windowsMode) {
+              // Just add the new missing rows on Windows as conpty reprints the screen with it's
+              // view of the world. Once a line enters scrollback for conpty it remains there
               this.lines.push(new BufferLine(newCols, nullCell));
+            } else {
+              if (this.ybase > 0 && this.lines.length <= this.ybase + this.y + addToY + 1) {
+                // There is room above the buffer and there are no empty elements below the line,
+                // scroll up
+                this.ybase--;
+                addToY++;
+                if (this.ydisp > 0) {
+                  // Viewport is at the top of the buffer, must increase downwards
+                  this.ydisp--;
+                }
+              } else {
+                // Add a blank line if there is no buffer left at the top to scroll to, or if there
+                // are blank lines after the cursor
+                this.lines.push(new BufferLine(newCols, nullCell));
+              }
             }
           }
         }