Bug 1610066 - Make nsTArray::SafeElementAt not require the complete type for smart pointers. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D60338

--HG--
extra : moz-landing-system : lando

xpcom/ds/nsTArray.h

@@ -264,12 +264,20 @@ struct nsTArray_SafeElementAtSmartPtrHelper {
   typedef size_t index_type;
 
   elem_type SafeElementAt(index_type aIndex) {
-    return static_cast<Derived*>(this)->SafeElementAt(aIndex, nullptr);
+    auto* derived = static_cast<Derived*>(this);
+    if (aIndex < derived->Length()) {
+      return derived->Elements()[aIndex];
+    }
+    return nullptr;
   }
 
   // XXX: Probably should return const_elem_type, but callsites must be fixed.
   elem_type SafeElementAt(index_type aIndex) const {
-    return static_cast<const Derived*>(this)->SafeElementAt(aIndex, nullptr);
+    auto* derived = static_cast<const Derived*>(this);
+    if (aIndex < derived->Length()) {
+      return derived->Elements()[aIndex];
+    }
+    return nullptr;
   }
 };
 
@@ -290,26 +298,8 @@ class OwningNonNull;
 }  // namespace mozilla
 
 template <class E, class Derived>
-struct nsTArray_SafeElementAtHelper<mozilla::OwningNonNull<E>, Derived> {
+struct nsTArray_SafeElementAtHelper<mozilla::OwningNonNull<E>, Derived>
-  typedef E* elem_type;
+    : public nsTArray_SafeElementAtSmartPtrHelper<E, Derived> {};
-  typedef const E* const_elem_type;
-  typedef size_t index_type;
-
-  elem_type SafeElementAt(index_type aIndex) {
-    if (aIndex < static_cast<Derived*>(this)->Length()) {
-      return static_cast<Derived*>(this)->ElementAt(aIndex);
-    }
-    return nullptr;
-  }
-
-  // XXX: Probably should return const_elem_type, but callsites must be fixed.
-  elem_type SafeElementAt(index_type aIndex) const {
-    if (aIndex < static_cast<const Derived*>(this)->Length()) {
-      return static_cast<const Derived*>(this)->ElementAt(aIndex);
-    }
-    return nullptr;
-  }
-};
 
 // Servo bindings.
 extern "C" void Gecko_EnsureTArrayCapacity(void* aArray, size_t aCapacity,

xpcom/tests/gtest/TestTArray.cpp

@@ -7,6 +7,7 @@
 #include "nsTArray.h"
 #include "gtest/gtest.h"
 #include "mozilla/ArrayUtils.h"
+#include "mozilla/RefPtr.h"
 
 using namespace mozilla;
 
@@ -461,4 +462,17 @@ TEST(TArray, MakeBackInserter)
   ASSERT_EQ(expected, dst);
 }
 
+// This should compile:
+struct RefCounted;
+
+class Foo {
+  ~Foo(); // Intentionally out of line
+
+  nsTArray<RefPtr<RefCounted>> mArray;
+
+  const RefCounted* GetFirst() const {
+    return mArray.SafeElementAt(0);
+  }
+};
+
 }  // namespace TestTArray