fix https://github.com/microsoft/vscode/issues/187779

src/vs/editor/contrib/suggest/browser/suggestModel.ts

@@ -635,6 +635,12 @@ export class SuggestModel implements IDisposable {
 			return;
 		}
 
+		if (!ctx.leadingLineContent.startsWith(this._context.leadingLineContent) && !this._context.leadingLineContent.startsWith(ctx.leadingLineContent)) {
+			// e.g. happens when line prefix changes, e.g delete while suggest is showing
+			this.cancel();
+			return;
+		}
+
 		if (getLeadingWhitespace(ctx.leadingLineContent) !== getLeadingWhitespace(this._context.leadingLineContent)) {
 			// cancel IntelliSense when line start changes
 			// happens when the current word gets outdented

src/vs/editor/contrib/suggest/test/browser/suggestController.test.ts

@@ -32,6 +32,7 @@ import { IWorkspaceContextService } from 'vs/platform/workspace/common/workspace
 import { LanguageFeaturesService } from 'vs/editor/common/services/languageFeaturesService';
 import { ILanguageFeaturesService } from 'vs/editor/common/services/languageFeatures';
 import { IEnvironmentService } from 'vs/platform/environment/common/environment';
+import { DeleteLinesAction } from 'vs/editor/contrib/linesOperations/browser/linesOperations';
 
 suite('SuggestController', function () {
 
@@ -579,4 +580,38 @@ suite('SuggestController', function () {
 		controller.acceptSelectedSuggestion(false, false);
 		assert.strictEqual(editor.getValue(), 'for');
 	});
+
+	test('Suggest widget gets orphaned in editor #187779', async function () {
+
+		disposables.add(languageFeaturesService.completionProvider.register({ scheme: 'test-ctrl' }, {
+			_debugDisplayName: 'test',
+			provideCompletionItems(doc, pos) {
+
+				const word = doc.getLineContent(pos.lineNumber);
+				const range = new Range(pos.lineNumber, 1, pos.lineNumber, pos.column);
+
+				return {
+					suggestions: [{
+						kind: CompletionItemKind.Text,
+						label: word,
+						insertText: word,
+						range
+					}]
+				};
+			}
+		}));
+
+		editor.setValue(`console.log(example.)\nconsole.log(EXAMPLE.not)`);
+		editor.setSelection(new Selection(1, 21, 1, 21));
+
+		const p1 = Event.toPromise(controller.model.onDidSuggest);
+		controller.triggerSuggest();
+
+		await p1;
+
+		const p2 = Event.toPromise(controller.model.onDidCancel);
+		new DeleteLinesAction().run(null!, editor);
+
+		await p2;
+	});
 });