Add a test for a corner case missed by #41978.

A member reference to a function with a dynamic 'Self' result type
can introduce a covariant return expression into the AST. This is
exposed by the (already deeply cursed) -self method on NSObject(Protocol).
Add a regression test and said cursed member to the mock SDK.

Author: CodaFi

lib/AST/Expr.cpp

@@ -1906,6 +1906,12 @@ Expr *AutoClosureExpr::getUnwrappedCurryThunkExpr() const {
     return expr;
   };
 
+  auto maybeUnwrapConversions = [](Expr *expr) {
+    if (auto *covariantReturn = dyn_cast<CovariantReturnConversionExpr>(expr))
+      expr = covariantReturn->getSubExpr();
+    return expr;
+  };
+
   switch (getThunkKind()) {
   case AutoClosureExpr::Kind::None:
   case AutoClosureExpr::Kind::AsyncLet:
@@ -1916,6 +1922,7 @@ Expr *AutoClosureExpr::getUnwrappedCurryThunkExpr() const {
     body = body->getSemanticsProvidingExpr();
     body = maybeUnwrapOpenExistential(body);
     body = maybeUnwrapOptionalEval(body);
+    body = maybeUnwrapConversions(body);
 
     if (auto *outerCall = dyn_cast<ApplyExpr>(body)) {
       return outerCall->getFn();
@@ -1934,6 +1941,7 @@ Expr *AutoClosureExpr::getUnwrappedCurryThunkExpr() const {
       innerBody = innerBody->getSemanticsProvidingExpr();
       innerBody = maybeUnwrapOpenExistential(innerBody);
       innerBody = maybeUnwrapOptionalEval(innerBody);
+      innerBody = maybeUnwrapConversions(innerBody);
 
       if (auto *outerCall = dyn_cast<ApplyExpr>(innerBody)) {
         if (auto *innerCall = dyn_cast<ApplyExpr>(outerCall->getFn())) {

test/Index/index_curry_thunk_objc.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk) -enable-objc-interop -print-indexed-symbols -source-filename %s | %FileCheck %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+@objc
+class Foo: NSObject {
+  // CHECK-DAG: constructor/Swift | init(object:)
+  init(object: Any?) {}
+}
+
+extension Foo {
+  // CHECK-DAG: static-property/Swift | boom
+  static let boom = Foo(object: self)
+}

test/Inputs/clang-importer-sdk/usr/include/objc/NSObject.h

@@ -6,6 +6,7 @@
 @class NSString;
 
 @protocol NSObject
+- (instancetype)self;
 @property (readonly, copy) NSString *description;
 - (instancetype)retain OBJC_ARC_UNAVAILABLE;
 - (Class)class;