Bug 1730096 part 6: Add AccAttributes::CopyTo to copy an AccAttributes. r=eeejay

This is necessary for two reasons:

1. Leaf text attributes and default text attributes are cached separately, since the caller can choose whether to include defaults or not. This means merging them together.
2. Methods for retrieving attributes currently return a non-const AccAttributes. We might be able to change this in future for some of them, but I didn't want to deal with that in this work.

Differential Revision: https://phabricator.services.mozilla.com/D129472

accessible/base/AccAttributes.cpp

@@ -98,3 +98,51 @@ bool AccAttributes::Equal(const AccAttributes* aOther) const {
   }
   return true;
 }
+
+void AccAttributes::CopyTo(AccAttributes* aDest) const {
+  for (auto iter = mData.ConstIter(); !iter.Done(); iter.Next()) {
+    iter.Data().match(
+        [&iter, &aDest](const bool& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const float& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const double& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const int32_t& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const RefPtr<nsAtom>& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [](const nsTArray<int32_t>& val) {
+          // We don't copy arrays.
+          MOZ_ASSERT_UNREACHABLE(
+              "Trying to copy an AccAttributes containing an array");
+        },
+        [&iter, &aDest](const CSSCoord& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const FontSize& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [&iter, &aDest](const Color& val) {
+          aDest->mData.InsertOrUpdate(iter.Key(), AsVariant(val));
+        },
+        [](const DeleteEntry& val) {
+          // We don't copy DeleteEntry.
+          MOZ_ASSERT_UNREACHABLE(
+              "Trying to copy an AccAttributes containing a DeleteEntry");
+        },
+        [&iter, &aDest](const UniquePtr<nsString>& val) {
+          aDest->SetAttributeStringCopy(iter.Key(), *val);
+        },
+        [](const RefPtr<AccAttributes>& val) {
+          // We don't copy nested AccAttributes.
+          MOZ_ASSERT_UNREACHABLE(
+              "Trying to copy an AccAttributes containing an AccAttributes");
+        });
+  }
+}

accessible/base/AccAttributes.h

@@ -151,6 +151,15 @@ class AccAttributes {
    */
   bool Equal(const AccAttributes* aOther) const;
 
+  /**
+   * Copy attributes from this instance to another instance.
+   * This should only be used in very specific cases; e.g. merging two sets of
+   * cached attributes without modifying the cache. It can only copy simple
+   * value types; e.g. it can't copy array values. Attempting to copy an
+   * AccAttributes with uncopyable values will cause an assertion.
+   */
+  void CopyTo(AccAttributes* aDest) const;
+
   // An entry class for our iterator.
   class Entry {
    public: