experiment: support tabstops after each case clause

Author: gabritto

Diff for: src/compiler/utilities.ts

@@ -90,7 +90,7 @@ import {
     TypePredicate, TypePredicateKind, TypeReferenceNode, unescapeLeadingUnderscores, UnionOrIntersectionTypeNode,
     ValidImportTypeNode, VariableDeclaration, VariableDeclarationInitializedTo, VariableDeclarationList,
     VariableLikeDeclaration, VariableStatement, version, WhileStatement, WithStatement, WriteFileCallback,
-    WriteFileCallbackData, YieldExpression, ResolutionMode, isIdentifierStart,
+    WriteFileCallbackData, YieldExpression, ResolutionMode, isIdentifierStart, getSnippetElement, SnippetKind,
 } from "./_namespaces/ts";
 
 /** @internal */
@@ -8691,3 +8691,8 @@ export function canUsePropertyAccess(name: string, languageVersion: ScriptTarget
         name.length > 1 && isIdentifierStart(name.charCodeAt(1), languageVersion) :
         isIdentifierStart(firstChar, languageVersion);
 }
+
+/** @internal */
+export function hasTabstop(node: Node): boolean {
+    return getSnippetElement(node)?.kind === SnippetKind.TabStop;
+}

Diff for: src/services/completions.ts

@@ -732,7 +732,12 @@ function getExhaustiveCaseSnippets(
             return undefined;
         }
 
-        const newClauses = map(elements, element => {
+        const newClauses = map(elements, (element, i) => {
+            if (preferences.includeCompletionsWithSnippetText) {
+                const tabstopStmt = factory.createEmptyStatement();
+                setSnippetElement(tabstopStmt, { kind: SnippetKind.TabStop, order: i + 1 });
+                return factory.createCaseClause(element, [tabstopStmt]);
+            }
             return factory.createCaseClause(element, []);
         });
         const printer = createSnippetPrinter({
@@ -752,7 +757,7 @@ function getExhaustiveCaseSnippets(
                 factory.createNodeArray(newClauses),
                 sourceFile);
 
-        const firstClause = printer.printSnippetList(ListFormat.SingleLine, factory.createNodeArray([first(newClauses)!]), sourceFile);
+        const firstClause = printer.printSnippetList(ListFormat.SingleLine, factory.createNodeArray([factory.createCaseClause(first(elements), [])]), sourceFile);
         return {
             entry: {
                 name: `${firstClause} ...`,
@@ -761,6 +766,7 @@ function getExhaustiveCaseSnippets(
                 insertText,
                 hasAction: importAdder.hasFixes() || undefined,
                 source: CompletionSource.SwitchCases,
+                isSnippet: preferences.includeCompletionsWithSnippetText ? true : undefined,
             },
             importAdder,
         };

Diff for: src/services/services.ts

@@ -54,7 +54,7 @@ import {
     TextRange, TextSpan, textSpanEnd, timestamp, TodoComment, TodoCommentDescriptor, Token, toPath, tracing,
     TransformFlags, TransientSymbol, Type, TypeChecker, TypeFlags, TypeNode, TypeParameter, TypePredicate,
     TypeReference, typeToDisplayParts, UnderscoreEscapedMap, UnionOrIntersectionType, UnionType, updateSourceFile,
-    UserPreferences, VariableDeclaration,
+    UserPreferences, VariableDeclaration, hasTabstop,
 } from "./_namespaces/ts";
 
 /** The version of the language service API */
@@ -234,6 +234,9 @@ function addSyntheticNodes(nodes: Push<Node>, pos: number, end: number, parent:
         const textPos = scanner.getTextPos();
         if (textPos <= end) {
             if (token === SyntaxKind.Identifier) {
+                if (hasTabstop(parent)) {
+                    continue;
+                }
                 Debug.fail(`Did not expect ${Debug.formatSyntaxKind(parent.kind)} to have an Identifier in its trivia`);
             }
             nodes.push(createNode(token, pos, textPos, parent));