Transfer all declared symbols onto the type from the interface that extends another

src/compiler/checker.ts

@@ -12829,7 +12829,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const baseTypes = getBaseTypes(source);
         if (baseTypes.length) {
             if (source.symbol && members === getMembersOfSymbol(source.symbol)) {
-                members = createSymbolTable(source.declaredProperties);
+                const symbolTable = createSymbolTable();
+                // copy all symbols (except type parameters), including the ones with internal names like `InternalSymbolName.Index`
+                for (const symbol of members.values()) {
+                    if (!(symbol.flags & SymbolFlags.TypeParameter)) {
+                        symbolTable.set(symbol.escapedName, symbol);
+                    }
+                }
+                members = symbolTable;
             }
             setStructuredTypeMembers(type, members, callSignatures, constructSignatures, indexInfos);
             const thisArgument = lastOrUndefined(typeArguments);

tests/baselines/reference/classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.symbols

@@ -0,0 +1,75 @@
+//// [tests/cases/compiler/classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts] ////
+
+=== classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts ===
+interface IObserver {
+>IObserver : Symbol(IObserver, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 0, 0))
+
+	handleChange<T, TChange>(observable: IObservable<T, TChange>, change: TChange): void;
+>handleChange : Symbol(IObserver.handleChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 0, 21))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 14))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 16))
+>observable : Symbol(observable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 26))
+>IObservable : Symbol(IObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 2, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 14))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 16))
+>change : Symbol(change, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 62))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 1, 16))
+}
+
+interface IObservable<T, TChange = unknown> {
+>IObservable : Symbol(IObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 2, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 22))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 24), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 5, 10))
+
+	get(): T;
+>get : Symbol(IObservable.get, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 45))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 22))
+
+	readonly TChange: TChange;
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 24), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 5, 10))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 4, 24), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 5, 10))
+}
+
+export interface IReader {
+>IReader : Symbol(IReader, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 7, 1))
+
+	readObservable<T>(observable: IObservable<T, any>): T;
+>readObservable : Symbol(IReader.readObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 9, 26))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 10, 16))
+>observable : Symbol(observable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 10, 19))
+>IObservable : Symbol(IObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 2, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 10, 16))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 10, 16))
+}
+
+export abstract class ConvenientObservable<T, TChange> implements IObservable<T, TChange> {
+>ConvenientObservable : Symbol(ConvenientObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 11, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 43))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 45), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 91))
+>IObservable : Symbol(IObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 2, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 43))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 45), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 91))
+
+	get TChange(): TChange { return null!; }
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 45), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 91))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 45), Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 91))
+
+	public abstract get(): T;
+>get : Symbol(ConvenientObservable.get, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 14, 41))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 13, 43))
+}
+
+export abstract class BaseObservable<T, TChange = void> extends ConvenientObservable<T, TChange> {
+>BaseObservable : Symbol(BaseObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 16, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 18, 37))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 18, 39))
+>ConvenientObservable : Symbol(ConvenientObservable, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 11, 1))
+>T : Symbol(T, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 18, 37))
+>TChange : Symbol(TChange, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 18, 39))
+
+	protected readonly observers = new Set<IObserver>();
+>observers : Symbol(BaseObservable.observers, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 18, 98))
+>Set : Symbol(Set, Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.collection.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+>IObserver : Symbol(IObserver, Decl(classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts, 0, 0))
+}
+

tests/baselines/reference/classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.types

@@ -0,0 +1,45 @@
+//// [tests/cases/compiler/classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts] ////
+
+=== classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts ===
+interface IObserver {
+	handleChange<T, TChange>(observable: IObservable<T, TChange>, change: TChange): void;
+>handleChange : <T, TChange>(observable: IObservable<T, TChange>, change: TChange) => void
+>observable : IObservable<T, TChange>
+>change : TChange
+}
+
+interface IObservable<T, TChange = unknown> {
+	get(): T;
+>get : () => T
+
+	readonly TChange: TChange;
+>TChange : TChange
+}
+
+export interface IReader {
+	readObservable<T>(observable: IObservable<T, any>): T;
+>readObservable : <T>(observable: IObservable<T, any>) => T
+>observable : IObservable<T, any>
+}
+
+export abstract class ConvenientObservable<T, TChange> implements IObservable<T, TChange> {
+>ConvenientObservable : ConvenientObservable<T, TChange>
+
+	get TChange(): TChange { return null!; }
+>TChange : TChange
+>null! : never
+
+	public abstract get(): T;
+>get : () => T
+}
+
+export abstract class BaseObservable<T, TChange = void> extends ConvenientObservable<T, TChange> {
+>BaseObservable : BaseObservable<T, TChange>
+>ConvenientObservable : ConvenientObservable<T, TChange>
+
+	protected readonly observers = new Set<IObserver>();
+>observers : Set<IObserver>
+>new Set<IObserver>() : Set<IObserver>
+>Set : SetConstructor
+}
+

tests/cases/compiler/classExtendingAbstractClassWithMemberCalledTheSameAsItsOwnTypeParam.ts

@@ -0,0 +1,25 @@
+// @strict: true
+// @lib: esnext
+// @noEmit: true
+
+interface IObserver {
+	handleChange<T, TChange>(observable: IObservable<T, TChange>, change: TChange): void;
+}
+
+interface IObservable<T, TChange = unknown> {
+	get(): T;
+	readonly TChange: TChange;
+}
+
+export interface IReader {
+	readObservable<T>(observable: IObservable<T, any>): T;
+}
+
+export abstract class ConvenientObservable<T, TChange> implements IObservable<T, TChange> {
+	get TChange(): TChange { return null!; }
+	public abstract get(): T;
+}
+
+export abstract class BaseObservable<T, TChange = void> extends ConvenientObservable<T, TChange> {
+	protected readonly observers = new Set<IObserver>();
+}

tests/cases/fourslash/quickInfoOnPropDeclaredUsingIndexSignatureOnInterfaceWithBase.ts

@@ -0,0 +1,12 @@
+/// <reference path="fourslash.ts" />
+
+// https://github.com/microsoft/TypeScript/issues/55251
+
+//// interface P {}
+//// interface B extends P {
+////   [k: string]: number;
+//// }
+//// declare const b: B;
+//// b.t/*1*/est = 10;
+
+verify.quickInfoAt("1", "(index) B[string]: number");