add snippet sequence

src/compiler/emitter.ts

@@ -1942,6 +1942,11 @@ namespace ts {
                 case SnippetKind.TabStop:
                     emitTabStop(snippet);
                     break;
+                case SnippetKind.Sequence:
+                    emitSequence(snippet);
+                    break;
+                default:
+                    return Debug.fail("Unsupported SnippetKind.");
             }
         }
 
@@ -1956,6 +1961,12 @@ namespace ts {
             nonEscapingWrite(`\$${snippet.order}`);
         }
 
+        function emitSequence(snippet: SnippetSequence) {
+            for (const s of snippet.snippets) {
+                emitTabStop(s);
+            }
+        }
+
         //
         // Identifiers
         //

src/compiler/types.ts

@@ -6828,7 +6828,7 @@ namespace ts {
     }
 
     /* @internal */
-    export type SnippetElement = TabStop | Placeholder;
+    export type SnippetElement = TabStop | Placeholder | SnippetSequence;
 
     /* @internal */
     export interface TabStop {
@@ -6842,6 +6842,12 @@ namespace ts {
         order: number;
     }
 
+    /* @internal */
+    export interface SnippetSequence {
+        kind: SnippetKind.Sequence;
+        snippets: TabStop[];
+    }
+
     // Reference: https://code.visualstudio.com/docs/editor/userdefinedsnippets#_snippet-syntax
     /* @internal */
     export const enum SnippetKind {
@@ -6849,6 +6855,7 @@ namespace ts {
         Placeholder,                            // `${1:foo}`
         Choice,                                 // `${1|one,two,three|}`
         Variable,                               // `$name`, `${name:default}`
+        Sequence,                               // A sequence of tabstops, e.g. `$1$0`
     }
 
     export const enum EmitFlags {

src/services/completions.ts

@@ -852,12 +852,19 @@ namespace ts.Completions {
         let tabstopStart = 1;
         if (preferences.includeCompletionsWithSnippetText) {
             isSnippet = true;
-            // We are adding a final tabstop (i.e. $0) in the body of the suggested member, if it has one.
+            // We are adding an initial and final tabstop (i.e. `$1$0`) in the body of the suggested member,
+            // if it has one.
             // Note: this assumes we won't have more than one body in the completion nodes, which should be the case.
-            const emptyStatement1 = factory.createExpressionStatement(factory.createIdentifier(""));
-            setSnippetElement(emptyStatement1, { kind: SnippetKind.TabStop, order: 1 });
+            const emptyStatement = factory.createExpressionStatement(factory.createIdentifier(""));
+            setSnippetElement(emptyStatement, {
+                kind: SnippetKind.Sequence,
+                snippets: [
+                    { kind: SnippetKind.TabStop, order: 1 },
+                    { kind: SnippetKind.TabStop, order: 0 },
+                ],
+            });
             tabstopStart = 2;
-            body = factory.createBlock([emptyStatement1], /* multiline */ true);
+            body = factory.createBlock([emptyStatement], /* multiline */ true);
         }
         else {
             body = factory.createBlock([], /* multiline */ true);

tests/cases/fourslash/completionsOverridingMethod2.ts

@@ -30,7 +30,7 @@ verify.completions({
             },
             isSnippet: true,
             insertText:
-"\"\\$usd\"(${2:a}: ${3:number}): ${4:number} {\n    $1\n}\n",
+"\"\\$usd\"(${2:a}: ${3:number}): ${4:number} {\n    $1$0\n}\n",
         }
     ],
 });