fix(40322): bad completions for string literal type as indexed access type object

src/services/stringCompletions.ts

@@ -130,7 +130,11 @@ namespace ts.Completions.StringCompletions {
                         //          bar: string;
                         //      }
                         //      let x: Foo["/*completion position*/"]
-                        return stringLiteralCompletionsFromProperties(typeChecker.getTypeFromTypeNode((grandParent as IndexedAccessTypeNode).objectType));
+                        const { indexType, objectType } = grandParent as IndexedAccessTypeNode;
+                        if (!rangeContainsPosition(indexType, position)) {
+                            return undefined;
+                        }
+                        return stringLiteralCompletionsFromProperties(typeChecker.getTypeFromTypeNode(objectType));
                     case SyntaxKind.ImportType:
                         return { kind: StringLiteralCompletionKind.Paths, paths: getStringLiteralCompletionsFromModuleNames(sourceFile, node, compilerOptions, host, typeChecker) };
                     case SyntaxKind.UnionType: {

tests/cases/fourslash/completionListsStringLiteralTypeAsIndexedAccessTypeObject.ts

@@ -0,0 +1,47 @@
+/// <reference path="fourslash.ts" />
+
+//// let firstCase: "a/*case_1*/"["foo"]
+//// let secondCase: "b/*case_2*/"["bar"]
+//// let thirdCase: "c/*case_3*/"["baz"]
+//// let fourthCase: "en/*case_4*/"["qux"]
+//// interface Foo {
+////  bar: string;
+////  qux: string;
+//// }
+//// let fifthCase: Foo["b/*case_5*/"]
+//// let sixthCase: Foo["qu/*case_6*/"]
+
+// fourslash tests for issue 40322
+verify.completions({
+  marker: ["case_1", "case_2", "case_3", "case_4"],
+  exact: undefined,
+  isNewIdentifierLocation: true,
+});
+
+// regression tests
+const test5 = test.marker("case_5");
+const test6 = test.marker("case_6");
+
+verify.completions({
+  marker: "case_5",
+  includes: {
+    name: "bar",
+    replacementSpan: {
+      fileName: test5.fileName,
+      pos: test5.position - 1,
+      end: test5.position,
+    },
+  },
+});
+
+verify.completions({
+  marker: "case_6",
+  includes: {
+    name: "qux",
+    replacementSpan: {
+      fileName: test6.fileName,
+      pos: test6.position - 2,
+      end: test6.position,
+    },
+  },
+});