putty-style ED2 sequence handling as terminal option

Author: Blashaq

src/common/InputHandler.test.ts

@@ -438,6 +438,37 @@ describe('InputHandler', () => {
       inputHandler.eraseInLine(Params.fromArray([2]));
       assert.equal(bufferService.buffer.lines.get(2)!.isWrapped, false);
     });
+    it('ED2 with scrollOnDisplayErase turned on', async () => {
+      const inputHandler = new TestInputHandler(
+        bufferService,
+        new MockCharsetService(),
+        new MockCoreService(),
+        new MockLogService(),
+        new MockOptionsService({ scrollOnDisplayErase: true }),
+        new MockOscLinkService(),
+        new MockCoreMouseService(),
+        new MockUnicodeService()
+      );
+      const aLine = Array(bufferService.cols + 1).join('a');
+      // add 2 full lines of text.
+      await inputHandler.parseP(aLine);
+      await inputHandler.parseP(aLine);
+
+      inputHandler.eraseInDisplay(Params.fromArray([2]));
+      // those 2 lines should have been pushed to scrollback.
+      assert.equal(bufferService.rows + 2, bufferService.buffer.lines.length);
+      assert.equal(bufferService.buffer.ybase, 2);
+      assert.equal(bufferService.buffer.lines.get(0)?.translateToString(), aLine);
+      assert.equal(bufferService.buffer.lines.get(1)?.translateToString(), aLine);
+
+      // Move to last line and add more text.
+      bufferService.buffer.y = bufferService.rows - 1;
+      bufferService.buffer.x = 0;
+      await inputHandler.parseP(aLine);
+      inputHandler.eraseInDisplay(Params.fromArray([2]));
+      // Screen should have been scrolled by a full screen size.
+      assert.equal(bufferService.rows * 2 + 2, bufferService.buffer.lines.length);
+    });
     it('eraseInDisplay', async () => {
       const bufferService = new MockBufferService(80, 7);
       const inputHandler = new TestInputHandler(

src/common/InputHandler.ts

@@ -1220,12 +1220,30 @@ export class InputHandler extends Disposable implements IInputHandler {
         this._dirtyRowTracker.markDirty(0);
         break;
       case 2:
-        j = this._bufferService.rows;
-        this._dirtyRowTracker.markDirty(j - 1);
-        while (j--) {
-          this._resetBufferLine(j, respectProtect);
+        if (this._optionsService.rawOptions.scrollOnDisplayErase) {
+          let fouldLastLineToKeep = false;
+          j = this._bufferService.rows;
+          const x = this._activeBuffer.getBlankLine(this._eraseAttrData());
+          while (j > 0 && !fouldLastLineToKeep) {
+            j--;
+            const currentLine = this._activeBuffer.lines.get(this._activeBuffer.ybase + j);
+            if (currentLine?.translateToString() !== x.translateToString()) {
+              fouldLastLineToKeep = true;
+              this._dirtyRowTracker.markRangeDirty(0, j);
+            }
+          }
+          for (; j >= 0; j--) {
+            this._bufferService.scroll(this._eraseAttrData());
+          }
+        }
+        else {
+          j = this._bufferService.rows;
+          this._dirtyRowTracker.markDirty(j - 1);
+          while (j--) {
+            this._resetBufferLine(j, respectProtect);
+          }
+          this._dirtyRowTracker.markDirty(0);
         }
-        this._dirtyRowTracker.markDirty(0);
         break;
       case 3:
         // Clear scrollback (everything not in viewport)

src/common/services/OptionsService.ts

@@ -54,7 +54,8 @@ export const DEFAULT_OPTIONS: Readonly<Required<ITerminalOptions>> = {
   convertEol: false,
   termName: 'xterm',
   cancelEvents: false,
-  overviewRuler: {}
+  overviewRuler: {},
+  scrollOnDisplayErase: false
 };
 
 const FONT_WEIGHT_OPTIONS: Extract<FontWeight, string>[] = ['normal', 'bold', '100', '200', '300', '400', '500', '600', '700', '800', '900'];

typings/xterm-headless.d.ts

@@ -248,6 +248,12 @@ declare module '@xterm/headless' {
      * All features are disabled by default for security reasons.
      */
     windowOptions?: IWindowOptions;
+
+     /**
+     * If enabled ED2 (clear screen) escape sequence will push erased text to scrollback.
+     * This emulates PuTTY default clear screen behaviour.
+     */
+     scrollOnDisplayErase?: boolean
   }
 
   /**

typings/xterm.d.ts

@@ -331,6 +331,12 @@ declare module '@xterm/xterm' {
      * decorations underneath the scroll bar.
      */
     overviewRuler?: IOverviewRulerOptions;
+
+    /**
+     * If enabled ED2 (clear screen) escape sequence will push erased text to scrollback.
+     * This emulates PuTTY default clear screen behaviour.
+     */
+    scrollOnDisplayErase?: boolean
   }
 
   /**