fix #30769

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

@@ -27,6 +27,7 @@ export class OneSnippet {
 	private _placeholderDecorations: Map<Placeholder, string>;
 	private _placeholderGroups: Placeholder[][];
 	private _placeholderGroupsIdx: number;
+	private _syntheticFinalPlaceholderIndexPool: number = 1 << 30;
 
 	private static readonly _decor = {
 		active: ModelDecorationOptions.register({ stickiness: TrackedRangeStickiness.AlwaysGrowsWhenTypingAtEdges, className: 'snippet-placeholder' }),
@@ -173,7 +174,7 @@ export class OneSnippet {
 				// through the placeholders in the correct order
 				for (const nestedPlaceholder of nested._snippet.placeholders) {
 					if (nestedPlaceholder.isFinalTabstop) {
-						nestedPlaceholder.index = placeholder.index + (nested._snippet.placeholders.length / 10);
+						nestedPlaceholder.index = placeholder.index + (this._syntheticFinalPlaceholderIndexPool-- / 10);
 					} else {
 						nestedPlaceholder.index = placeholder.index + (nestedPlaceholder.index / 10);
 					}

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

@@ -433,5 +433,28 @@ suite('SnippetSession', function () {
 		session.prev();
 		assertSelections(editor, new Selection(1, 6, 1, 25));
 	});
+
+	test('Snippet placeholder index incorrect after using 2+ snippets in a row that each end with a placeholder, #30769', function () {
+		editor.getModel().setValue('');
+		editor.setSelection(new Selection(1, 1, 1, 1));
+		const session = new SnippetSession(editor, 'test ${1:replaceme}');
+		session.insert();
+
+		editor.trigger('test', 'type', { text: '1' });
+		editor.trigger('test', 'type', { text: '\n' });
+		assert.equal(editor.getModel().getValue(), 'test 1\n');
+
+		session.merge('test ${1:replaceme}');
+		editor.trigger('test', 'type', { text: '2' });
+		editor.trigger('test', 'type', { text: '\n' });
+
+		assert.equal(editor.getModel().getValue(), 'test 1\ntest 2\n');
+
+		session.merge('test ${1:replaceme}');
+		editor.trigger('test', 'type', { text: '3' });
+		editor.trigger('test', 'type', { text: '\n' });
+
+		assert.equal(editor.getModel().getValue(), 'test 1\ntest 2\ntest 3\n');
+	});
 });