1 files changed, 56 insertions, 0 deletions
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/union_declaration.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/union_declaration.tmpl
new file mode 100644
index 0000000000..005ba76b61
--- /dev/null
+++ b/mojo/public/tools/bindings/generators/cpp_templates/union_declaration.tmpl
@@ -0,0 +1,56 @@
+{%- set class_name = union.name ~ "_Data" -%}
+{%- set enum_name = union.name ~ "_Tag" -%}
+{%- import "struct_macros.tmpl" as struct_macros %}
+
+class {{class_name}} {
+ public:
+  // Used to identify Mojom Union Data Classes.
+  typedef void MojomUnionDataType;
+
+  {{class_name}}() {}
+  // Do nothing in the destructor since it won't be called when it is a
+  // non-inlined union.
+  ~{{class_name}}() {}
+
+  static {{class_name}}* New(mojo::internal::Buffer* buf) {
+    return new (buf->Allocate(sizeof({{class_name}}))) {{class_name}}();
+  }
+
+  static bool Validate(const void* data,
+                       mojo::internal::ValidationContext* validation_context,
+                       bool inlined);
+
+  bool is_null() const { return size == 0; }
+
+  void set_null() {
+    size = 0U;
+    tag = static_cast<{{enum_name}}>(0);
+    data.unknown = 0U;
+  }
+
+  enum class {{enum_name}} : uint32_t {
+{%  for field in union.fields %}
+    {{field.name|upper}},
+{%- endfor %}
+  };
+
+  // A note on layout:
+  // "Each non-static data member is allocated as if it were the sole member of
+  // a struct." - Section 9.5.2 ISO/IEC 14882:2011 (The C++ Spec)
+  union MOJO_ALIGNAS(8) Union_ {
+{%- for field in union.fields %}
+{%-   if field.kind.spec == 'b' %}
+    uint8_t f_{{field.name}} : 1;
+{%-   else %}
+    {{field.kind|cpp_union_field_type}} f_{{field.name}};
+{%-   endif %}
+{%- endfor %}
+    uint64_t unknown;
+  };
+
+  uint32_t size;
+  {{enum_name}} tag;
+  Union_ data;
+};
+static_assert(sizeof({{class_name}}) == mojo::internal::kUnionDataSize,
+              "Bad sizeof({{class_name}})");