stricter definition for what a trival snippet it (#165355)

fixes https://github.com/microsoft/vscode/issues/163808

src/vs/editor/contrib/snippet/browser/snippetParser.ts

@@ -165,6 +165,13 @@ export abstract class Marker {
 		return this._children;
 	}
 
+	get rightMostDescendant(): Marker {
+		if (this._children.length > 0) {
+			return this._children[this._children.length - 1].rightMostDescendant;
+		}
+		return this;
+	}
+
 	get snippet(): TextmateSnippet | undefined {
 		let candidate: Marker = this;
 		while (true) {

src/vs/editor/contrib/snippet/browser/snippetSession.ts

@@ -208,9 +208,23 @@ export class OneSnippet {
 		return this._snippet.placeholders.length > 0;
 	}
 
+	/**
+	 * A snippet is trivial when it has no placeholder or only a final placeholder at
+	 * its very end
+	 */
 	get isTrivialSnippet(): boolean {
-		return this._snippet.placeholders.length === 0
-			|| (this._snippet.placeholders.length === 1 && this._snippet.placeholders[0].isFinalTabstop);
+		if (this._snippet.placeholders.length === 0) {
+			return true;
+		}
+		if (this._snippet.placeholders.length === 1) {
+			const [placeholder] = this._snippet.placeholders;
+			if (placeholder.isFinalTabstop) {
+				if (this._snippet.rightMostDescendant === placeholder) {
+					return true;
+				}
+			}
+		}
+		return false;
 	}
 
 	computePossibleSelections() {

src/vs/editor/contrib/snippet/test/browser/snippetController2.test.ts

@@ -692,4 +692,18 @@ suite('SnippetController2', function () {
 			assert.deepStrictEqual(editor.getSelections(), [new Selection(1, 5, 1, 5), new Selection(1, 10, 1, 10), new Selection(2, 5, 2, 5), new Selection(2, 10, 2, 10)]);
 		});
 	});
+
+	test('Bug: cursor position $0 with user snippets #163808', function () {
+
+		const ctrl = instaService.createInstance(SnippetController2, editor);
+		model.setValue('');
+
+		ctrl.insert('<Element1 Attr1="foo" $1>\n  <Element2 Attr1="$2"/>\n$0"\n</Element1>');
+		assert.deepStrictEqual(editor.getSelections(), [new Selection(1, 23, 1, 23)]);
+
+		ctrl.insert('Qualifier="$0"');
+		assert.strictEqual(model.getValue(), '<Element1 Attr1="foo" Qualifier="">\n  <Element2 Attr1=""/>\n"\n</Element1>');
+		assert.deepStrictEqual(editor.getSelections(), [new Selection(1, 34, 1, 34)]);
+
+	});
 });