Merge pull request #4625 from timbodeit/SR-1681

[Sema] Fix SR-1681 spurious "unused result" warning

Author: slavapestov

lib/Sema/TypeCheckStmt.cpp

@@ -1080,9 +1080,12 @@ void TypeChecker::checkIgnoredExpr(Expr *E) {
   // If we have an OptionalEvaluationExpr at the top level, then someone is
   // "optional chaining" and ignoring the result.  Produce a diagnostic if it
   // doesn't make sense to ignore it.
-  if (auto *OEE = dyn_cast<OptionalEvaluationExpr>(valueE))
+  if (auto *OEE = dyn_cast<OptionalEvaluationExpr>(valueE)) {
     if (auto *IIO = dyn_cast<InjectIntoOptionalExpr>(OEE->getSubExpr()))
       return checkIgnoredExpr(IIO->getSubExpr());
+    if (auto *C = dyn_cast<CallExpr>(OEE->getSubExpr()))
+      return checkIgnoredExpr(C);
+  }
 
   // Check if we have a call to a function not marked with
   // '@discardableResult'.

test/attr/attr_discardableResult.swift

@@ -42,6 +42,11 @@ class C1 {
 
   func f2() -> Int { }
 
+  @discardableResult
+  func f1Optional() -> Int? { }
+
+  func f2Optional() -> Int? { }
+
   @discardableResult
   func me() -> Self { return self }
 
@@ -68,6 +73,10 @@ func testFunctionsInClass(c1 : C1, c2: C2) {
   c1.f2()           // expected-warning {{result of call to 'f2()' is unused}}
   _ = c1.f2()       // okay
 
+  c1.f1Optional()   // okay
+  c1.f2Optional()   // expected-warning {{result of call to 'f2Optional()' is unused}}
+  _ = c1.f2Optional() // okay
+
   c1.me()           // okay
   c2.me()           // okay
 
@@ -91,6 +100,11 @@ struct S1 {
   func f1() -> Int { }
 
   func f2() -> Int { }
+
+  @discardableResult
+  func f1Optional() -> Int? { }
+
+  func f2Optional() -> Int? { }
 }
 
 func testFunctionsInStruct(s1 : S1) {
@@ -106,6 +120,10 @@ func testFunctionsInStruct(s1 : S1) {
   s1.f1()           // okay
   s1.f2()           // expected-warning {{result of call to 'f2()' is unused}}
   _ = s1.f2()       // okay
+
+  s1.f1Optional()   // okay
+  s1.f2Optional()   // expected-warning {{result of call to 'f2Optional()' is unused}}
+  _ = s1.f2Optional() // okay
 }
 
 protocol P1 {
@@ -138,3 +156,23 @@ class X {
   @objc
   func h() -> Int { }
 }
+
+func testOptionalChaining(c1: C1?, s1: S1?) {
+  c1?.f1()         // okay
+  c1!.f1()         // okay
+  c1?.f1Optional() // okay
+  c1!.f1Optional() // okay
+  c1?.f2()         // expected-warning {{result of call to 'f2()' is unused}}
+  c1!.f2()         // expected-warning {{result of call to 'f2()' is unused}}
+  c1?.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
+  c1!.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
+
+  s1?.f1()         // okay
+  s1!.f1()         // okay
+  s1?.f1Optional() // okay
+  s1!.f1Optional() // okay
+  s1?.f2()         // expected-warning {{result of call to 'f2()' is unused}}
+  s1!.f2()         // expected-warning {{result of call to 'f2()' is unused}}
+  s1?.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
+  s1!.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
+}