Return string completions for indexed access types

src/compiler/utilities.ts

@@ -4403,7 +4403,7 @@ namespace ts {
         return node.kind === SyntaxKind.RegularExpressionLiteral;
     }
 
-    export function isNoSubstitutionTemplateLiteral(node: Node): node is LiteralExpression {
+    export function isNoSubstitutionTemplateLiteral(node: Node): node is NoSubstitutionTemplateLiteral {
         return node.kind === SyntaxKind.NoSubstitutionTemplateLiteral;
     }
 

src/services/completions.ts

@@ -264,7 +264,8 @@ namespace ts.Completions {
             // }
             // let a: A;
             // a['/*completion position*/']
-            return getStringLiteralCompletionEntriesFromElementAccess(node.parent, typeChecker, compilerOptions.target, log);
+            const type = typeChecker.getTypeAtLocation(node.parent.expression);
+            return getStringLiteralCompletionEntriesFromElementAccessOrIndexedAccess(node, type, typeChecker, compilerOptions.target, log);
         }
         else if (node.parent.kind === SyntaxKind.ImportDeclaration || node.parent.kind === SyntaxKind.ExportDeclaration
             || isRequireCall(node.parent, /*checkArgumentIsStringLiteral*/ false) || isImportCall(node.parent)
@@ -278,6 +279,16 @@ namespace ts.Completions {
             const entries = PathCompletions.getStringLiteralCompletionsFromModuleNames(node, compilerOptions, host, typeChecker);
             return pathCompletionsInfo(entries);
         }
+        else if (isIndexedAccessTypeNode(node.parent.parent)) {
+            // Get all apparent property names
+            // i.e. interface Foo {
+            //          foo: string;
+            //          bar: string;
+            //      }
+            //      let x: Foo["/*completion position*/"]
+            const type = typeChecker.getTypeFromTypeNode(node.parent.parent.objectType);
+            return getStringLiteralCompletionEntriesFromElementAccessOrIndexedAccess(node, type, typeChecker, compilerOptions.target, log);
+        }
         else {
             const argumentInfo = SignatureHelp.getImmediatelyContainingArgumentInfo(node, position, sourceFile);
             if (argumentInfo) {
@@ -334,11 +345,10 @@ namespace ts.Completions {
         return undefined;
     }
 
-    function getStringLiteralCompletionEntriesFromElementAccess(node: ElementAccessExpression, typeChecker: TypeChecker, target: ScriptTarget, log: Log): CompletionInfo | undefined {
-        const type = typeChecker.getTypeAtLocation(node.expression);
+    function getStringLiteralCompletionEntriesFromElementAccessOrIndexedAccess(stringLiteralNode: StringLiteral | NoSubstitutionTemplateLiteral, type: Type, typeChecker: TypeChecker, target: ScriptTarget, log: Log): CompletionInfo | undefined {
         const entries: CompletionEntry[] = [];
         if (type) {
-            getCompletionEntriesFromSymbols(type.getApparentProperties(), entries, node, /*performCharacterChecks*/ false, typeChecker, target, log, /*allowStringLiteral*/ true);
+            getCompletionEntriesFromSymbols(type.getApparentProperties(), entries, stringLiteralNode, /*performCharacterChecks*/ false, typeChecker, target, log, /*allowStringLiteral*/ true);
             if (entries.length) {
                 return { isGlobalCompletion: false, isMemberCompletion: true, isNewIdentifierLocation: true, entries };
             }
@@ -1583,7 +1593,7 @@ namespace ts.Completions {
                 switch (contextToken.kind) {
                     case SyntaxKind.OpenParenToken:
                     case SyntaxKind.CommaToken:
-                        return  isConstructorDeclaration(contextToken.parent) && contextToken.parent;
+                        return isConstructorDeclaration(contextToken.parent) && contextToken.parent;
 
                     default:
                         if (isConstructorParameterCompletion(contextToken)) {

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2911,7 +2911,7 @@ declare namespace ts {
     function isStringLiteral(node: Node): node is StringLiteral;
     function isJsxText(node: Node): node is JsxText;
     function isRegularExpressionLiteral(node: Node): node is RegularExpressionLiteral;
-    function isNoSubstitutionTemplateLiteral(node: Node): node is LiteralExpression;
+    function isNoSubstitutionTemplateLiteral(node: Node): node is NoSubstitutionTemplateLiteral;
     function isTemplateHead(node: Node): node is TemplateHead;
     function isTemplateMiddle(node: Node): node is TemplateMiddle;
     function isTemplateTail(node: Node): node is TemplateTail;

tests/baselines/reference/api/typescript.d.ts

@@ -2964,7 +2964,7 @@ declare namespace ts {
     function isStringLiteral(node: Node): node is StringLiteral;
     function isJsxText(node: Node): node is JsxText;
     function isRegularExpressionLiteral(node: Node): node is RegularExpressionLiteral;
-    function isNoSubstitutionTemplateLiteral(node: Node): node is LiteralExpression;
+    function isNoSubstitutionTemplateLiteral(node: Node): node is NoSubstitutionTemplateLiteral;
     function isTemplateHead(node: Node): node is TemplateHead;
     function isTemplateMiddle(node: Node): node is TemplateMiddle;
     function isTemplateTail(node: Node): node is TemplateTail;

tests/cases/fourslash/completionForStringLiteralInIndexedAccess01.ts

@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts'/>
+
+////interface Foo {
+////    foo: string;
+////    bar: string;
+////}
+////
+////let x: Foo["/*1*/"]
+
+goTo.marker("1");
+verify.completionListContains("foo");
+verify.completionListContains("bar");
+verify.completionListCount(2);