Fix AttrSystemInitialValue on overridden properties

Summary:
If its set on the parent prop, but not on the child, we need to
explicitly clear it on the child's property.

Reviewed By: ricklavoie

Differential Revision: D13084126

fbshipit-source-id: 3de06f6239f770efe60a3da582060c5fbab6d4dc

hphp/runtime/vm/class.cpp

@@ -2594,9 +2594,9 @@ void Class::setProperties() {
         if (preProp->attrs() & AttrNoImplicitNullable) {
           prop.attrs |= AttrNoImplicitNullable;
         }
-        if (preProp->attrs() & AttrSystemInitialValue) {
-          prop.attrs |= AttrSystemInitialValue;
-        }
+        attrSetter(prop.attrs,
+                   preProp->attrs() & AttrSystemInitialValue,
+                   AttrSystemInitialValue);
         if (preProp->attrs() & AttrInitialSatisfiesTC) {
           prop.attrs |= AttrInitialSatisfiesTC;
         }
@@ -2651,9 +2651,9 @@ void Class::setProperties() {
         if (preProp->attrs() & AttrNoImplicitNullable) {
           prop.attrs |= AttrNoImplicitNullable;
         }
-        if (preProp->attrs() & AttrSystemInitialValue) {
-          prop.attrs |= AttrSystemInitialValue;
-        }
+        attrSetter(prop.attrs,
+                   preProp->attrs() & AttrSystemInitialValue,
+                   AttrSystemInitialValue);
         if (preProp->attrs() & AttrInitialSatisfiesTC) {
           prop.attrs |= AttrInitialSatisfiesTC;
         }

hphp/test/slow/object_property/system_initial_value.php

@@ -0,0 +1,36 @@
+<?hh
+
+class Y {
+  const A = 'a';
+}
+
+class A {
+  public ImmMap $pub;
+  protected ImmMap $prot;
+}
+
+class X extends A {
+  public ImmMap $pub = ImmMap {
+    Y::A => 42,
+  };
+  protected ImmMap $prot = ImmMap {
+    Y::A => 24,
+  };
+
+  function getPub() { return $this->pub; }
+  function getProt() { return $this->prot; }
+}
+
+function test() {
+  return new X;
+}
+
+function main() {
+  for ($i = 1; $i < 100; $i++) {
+    test();
+  }
+  $x = test();
+  var_dump($x->getPub(), $x->getProt());
+}
+
+main();

hphp/test/slow/object_property/system_initial_value.php.expect

@@ -0,0 +1,8 @@
+object(HH\ImmMap)#202 (1) {
+  ["a"]=>
+  int(42)
+}
+object(HH\ImmMap)#203 (1) {
+  ["a"]=>
+  int(24)
+}