[Chrome Cleaner] Simplify wstring_embedded_nulls.mojom

This change simplifies wstring_embedded_nulls.mojom by removing the
union and making it a simple struct wrapping an uint16 array.

Bug: 911896
Change-Id: Idd4042f6a7bee8f066f6ce6477d6e5967b4d12be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2320571
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792172}

chrome/chrome_cleaner/mojom/typemaps/wstring_embedded_nulls_mojom_traits.cc

@@ -9,53 +9,21 @@
 namespace mojo {
 
 using chrome_cleaner::WStringEmbeddedNulls;
-using chrome_cleaner::mojom::NullValueDataView;
 using chrome_cleaner::mojom::WStringEmbeddedNullsDataView;
 
-// static
-bool StructTraits<NullValueDataView, nullptr_t>::Read(NullValueDataView data,
-                                                      nullptr_t* value) {
-  *value = nullptr;
-  return true;
-}
-
 // static
 base::span<const uint16_t>
-UnionTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::value(
+StructTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::value(
     const WStringEmbeddedNulls& str) {
-  DCHECK_EQ(WStringEmbeddedNullsDataView::Tag::VALUE, GetTag(str));
-
   // This should only be called by Mojo to get the data to be send through the
   // pipe. When called by Mojo in this case, str will outlive the returned span.
   return base::make_span(str.CastAsUInt16Array(), str.size());
 }
 
 // static
-nullptr_t
-UnionTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::null_value(
-    const chrome_cleaner::WStringEmbeddedNulls& str) {
-  DCHECK_EQ(WStringEmbeddedNullsDataView::Tag::NULL_VALUE, GetTag(str));
-
-  return nullptr;
-}
-
-// static
-chrome_cleaner::mojom::WStringEmbeddedNullsDataView::Tag
-UnionTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::GetTag(
-    const chrome_cleaner::WStringEmbeddedNulls& str) {
-  return str.size() == 0 ? WStringEmbeddedNullsDataView::Tag::NULL_VALUE
-                         : WStringEmbeddedNullsDataView::Tag::VALUE;
-}
-
-// static
-bool UnionTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::Read(
+bool StructTraits<WStringEmbeddedNullsDataView, WStringEmbeddedNulls>::Read(
     WStringEmbeddedNullsDataView str_view,
     WStringEmbeddedNulls* out) {
-  if (str_view.is_null_value()) {
-    *out = WStringEmbeddedNulls();
-    return true;
-  }
-
   ArrayDataView<uint16_t> view;
   str_view.GetValueDataView(&view);
   // Note: Casting is intentional, since the data view represents the string as

chrome/chrome_cleaner/mojom/typemaps/wstring_embedded_nulls_mojom_traits.h

@@ -15,24 +15,13 @@
 
 namespace mojo {
 
-// Defines NullValue as mapped to nullptr_t.
 template <>
-struct StructTraits<chrome_cleaner::mojom::NullValueDataView, nullptr_t> {
-  static bool Read(chrome_cleaner::mojom::NullValueDataView data,
-                   nullptr_t* value);
-};
-
-template <>
-struct UnionTraits<chrome_cleaner::mojom::WStringEmbeddedNullsDataView,
-                   chrome_cleaner::WStringEmbeddedNulls> {
+struct StructTraits<chrome_cleaner::mojom::WStringEmbeddedNullsDataView,
+                    chrome_cleaner::WStringEmbeddedNulls> {
   // This should only be called by Mojo to marshal the object before sending it
   // through the pipe.
   static base::span<const uint16_t> value(
       const chrome_cleaner::WStringEmbeddedNulls& str);
-  static nullptr_t null_value(const chrome_cleaner::WStringEmbeddedNulls& str);
-
-  static chrome_cleaner::mojom::WStringEmbeddedNullsDataView::Tag GetTag(
-      const chrome_cleaner::WStringEmbeddedNulls& str);
 
   static bool Read(chrome_cleaner::mojom::WStringEmbeddedNullsDataView str_view,
                    chrome_cleaner::WStringEmbeddedNulls* out);

chrome/chrome_cleaner/mojom/wstring_embedded_nulls.mojom

@@ -5,20 +5,6 @@
 module chrome_cleaner.mojom;
 
 // Typemapped to chrome_cleaner::WStringEmbeddedNulls.
-//
-// Note: Mojo doesn't allow sending null arrays over the wire, and the strings
-//       represented by this type can be empty (without a null at the end).
-//       Because of that, represented as a union of either something that is
-//       always empty (NullValue) or a non-empty array of uint16.
-union WStringEmbeddedNulls {
-  // The underlying string is a null array (not the same as an empty string,
-  // which has at least one character '\0').
-  NullValue? null_value;
-
-  // The underlying string is either a null-terminated empty string (size is 1),
-  // or a non-empty string that can be either null-terminated or not.
+struct WStringEmbeddedNulls {
   array<uint16> value;
 };
-
-struct NullValue {
-};