There must always be at least one visible line (#44805)

src/vs/editor/common/viewModel/splitLinesCollection.ts

@@ -288,6 +288,7 @@ export class SplitLinesCollection implements IViewModelLinesCollection {
 		let hiddenAreaIdx = -1;
 		let nextLineNumberToUpdateHiddenArea = (hiddenAreaIdx + 1 < hiddenAreas.length) ? hiddenAreaEnd + 1 : this.lines.length + 2;
 
+		let hasVisibleLine = false;
 		for (let i = 0; i < this.lines.length; i++) {
 			let lineNumber = i + 1;
 
@@ -306,6 +307,7 @@ export class SplitLinesCollection implements IViewModelLinesCollection {
 					lineChanged = true;
 				}
 			} else {
+				hasVisibleLine = true;
 				// Line should be visible
 				if (!this.lines[i].isVisible()) {
 					this.lines[i] = this.lines[i].setVisible(true);
@@ -318,6 +320,11 @@ export class SplitLinesCollection implements IViewModelLinesCollection {
 			}
 		}
 
+		if (!hasVisibleLine) {
+			// Cannot have everything be hidden => reveal everything!
+			this.setHiddenAreas([]);
+		}
+
 		return true;
 	}
 
@@ -465,6 +472,10 @@ export class SplitLinesCollection implements IViewModelLinesCollection {
 
 	public acceptVersionId(versionId: number): void {
 		this._validModelVersionId = versionId;
+		if (this.lines.length === 1 && !this.lines[0].isVisible()) {
+			// At least one line must be visible => reset hidden areas
+			this.setHiddenAreas([]);
+		}
 	}
 
 	public getViewLineCount(): number {

src/vs/editor/test/common/viewModel/viewModelImpl.test.ts

@@ -74,6 +74,39 @@ suite('ViewModel', () => {
 		});
 	});
 
+	test('issue #44805: No visible lines via API call', () => {
+		const text = [
+			'line1',
+			'line2',
+			'line3'
+		];
+		testViewModel(text, {}, (viewModel, model) => {
+			assert.equal(viewModel.getLineCount(), 3);
+			viewModel.setHiddenAreas([new Range(1, 1, 3, 1)]);
+			assert.ok(viewModel.getVisibleRanges() !== null);
+		});
+	});
+
+	test('issue #44805: No visible lines via undoing', () => {
+		const text = [
+			''
+		];
+		testViewModel(text, {}, (viewModel, model) => {
+			assert.equal(viewModel.getLineCount(), 1);
+
+			model.pushEditOperations([], [{
+				range: new Range(1, 1, 1, 1),
+				text: 'line1\nline2\nline3'
+			}], () => ([]));
+
+			viewModel.setHiddenAreas([new Range(1, 1, 1, 1)]);
+			assert.equal(viewModel.getLineCount(), 2);
+
+			model.undo();
+			assert.ok(viewModel.getVisibleRanges() !== null);
+		});
+	});
+
 	function assertGetPlainTextToCopy(text: string[], ranges: Range[], emptySelectionClipboard: boolean, expected: string | string[]): void {
 		testViewModel(text, {}, (viewModel, model) => {
 			let actual = viewModel.getPlainTextToCopy(ranges, emptySelectionClipboard);