fix(39346): show completion in inherited classes from the composited base interface

src/services/completions.ts

@@ -2432,7 +2432,7 @@ namespace ts.Completions {
                 !existingMemberNames.has(propertySymbol.escapedName) &&
                 !!propertySymbol.declarations &&
                 !(getDeclarationModifierFlagsFromSymbol(propertySymbol) & ModifierFlags.Private) &&
-                !isPrivateIdentifierPropertyDeclaration(propertySymbol.valueDeclaration));
+                !(propertySymbol.valueDeclaration && isPrivateIdentifierPropertyDeclaration(propertySymbol.valueDeclaration)));
         }
 
         /**

tests/cases/fourslash/completionListInheritedClassMembers.ts

@@ -0,0 +1,43 @@
+/// <reference path="fourslash.ts"/>
+
+// @filename: a.ts
+////interface I {
+////    m2(): void;
+////    m3(): void;
+////}
+////
+////type T1 = I;
+////export interface A1 extends T1 {
+////    m1(): void;
+////}
+////export class A1 {}
+////
+////type T2 = Partial<I>
+////export interface A2 extends T2 {
+////    m1(): void;
+////}
+////export class A2 {}
+////
+////type T3 = Pick<I, "m3">
+////export interface A3 extends T3 {
+////    m1(): void;
+////}
+////export class A3 {}
+
+// @filename: b.ts
+////import { A1, A2, A3 } from './a';
+////class B1 extends A1 {
+////    /*1*/
+////}
+////class B2 extends A2 {
+////    /*2*/
+////}
+////class B3 extends A3 {
+////    /*3*/
+////}
+
+verify.completions(
+    { marker: "1", exact: ["m1", "m2", "m3", ...completion.classElementKeywords], isNewIdentifierLocation: true },
+    { marker: "2", exact: ["m1", "m2", "m3", ...completion.classElementKeywords], isNewIdentifierLocation: true },
+    { marker: "3", exact: ["m1", "m3", ...completion.classElementKeywords], isNewIdentifierLocation: true }
+);