[sema] Look through OpenExistentialExpr in checkIgnoreExpr()

Author: Suyash Srijan

lib/Sema/TypeCheckStmt.cpp

@@ -1312,6 +1312,8 @@ void TypeChecker::checkIgnoredExpr(Expr *E) {
       return checkIgnoredExpr(IIO->getSubExpr());
     if (auto *C = dyn_cast<CallExpr>(OEE->getSubExpr()))
       return checkIgnoredExpr(C);
+    if (auto *OE = dyn_cast<OpenExistentialExpr>(OEE->getSubExpr()))
+      return checkIgnoredExpr(OE);
   }
 
   if (auto *LE = dyn_cast<LiteralExpr>(valueE)) {

test/attr/attr_discardableResult.swift

@@ -194,3 +194,20 @@ class SR7562_B : SR7562_A {}
 
 SR7562_A(input: 10) // okay
 SR7562_B(input: 10) // okay
+
+protocol FooProtocol {}
+
+extension FooProtocol {
+  @discardableResult
+  static func returnSomething() -> Bool? {
+    return true
+  }
+}
+
+class Foo {
+  var myOptionalFooProtocol: FooProtocol.Type?
+  
+  func doSomething() {
+    myOptionalFooProtocol?.returnSomething() // okay
+  }
+}