[MiscDiagnostics] Suppress KVO warning when the property has an explicit setter (swiftlang#30098)

Author: theblixguy

lib/Sema/MiscDiagnostics.cpp

@@ -4337,7 +4337,10 @@ static void maybeDiagnoseCallToKeyValueObserveMethod(const Expr *E,
       auto property = lastComponent.getDeclRef().getDecl();
       if (!property)
         return;
-      if (property->isObjCDynamic())
+      auto propertyVar = cast<VarDecl>(property);
+      if (propertyVar->isObjCDynamic() ||
+          (propertyVar->isObjC() &&
+           propertyVar->getParsedAccessor(AccessorKind::Set)))
         return;
       C.Diags
           .diagnose(expr->getLoc(),

test/expr/primary/keypath/keypath-observe-objc.swift

@@ -8,6 +8,10 @@ class Foo: NSObject {
   dynamic var number2 = 2
   @objc var number3 = 3
   @objc dynamic var number4 = 4
+  @objc var number5: Int {
+    get { return 5 }
+    set {}
+  }
 }
 
 class Bar: NSObject {
@@ -35,5 +39,9 @@ class Bar: NSObject {
     _ = observe(\.foo.number4, options: [.new]) { _, change in // Okay
       print("observer4")
     }
+
+    _ = observe(\.foo.number5, options: [.new]) { _, change in // Okay
+      print("observer4")
+    }
   }
 }