bind-gen: Simplify the implementation of the union name

It turned out that concatenating the member type names is not
helpful to save APK size (it's slightly worse).  So, changes
it to a simple string literal.

Bug: 839389
Change-Id: I846ed6942460b2d8bb87b34065015686675a13f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2880934
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880773}

third_party/blink/renderer/bindings/scripts/bind_gen/union.py

@@ -408,9 +408,8 @@ def symbol_definition_constructor(symbol_node):
     else:
         # 19. Throw a TypeError.
         body.append(
-            T("${exception_state}.ThrowTypeError("
-              "ExceptionMessages::ValueNotOfType("
-              "UnionNameInIDL().Ascii().c_str()));"))
+            T("ThrowTypeErrorNotOfType"
+              "(${exception_state}, UnionNameInIDL());"))
         body.append(T("return nullptr;"))
 
     return func_decl, func_def
@@ -701,23 +700,19 @@ def make_name_function(cg_context):
 
     func_def = CxxFuncDefNode(name="UnionNameInIDL",
                               arg_decls=[],
-                              return_type="String",
-                              static=True)
+                              return_type="const char*",
+                              static=True,
+                              constexpr=True)
     func_def.set_base_template_vars(cg_context.template_bindings())
     body = func_def.body
 
-    body.extend([
-        TextNode("static constexpr const char* const member_names[] = {"),
-        ListNode(list(
-            map(
-                lambda name: TextNode("\"{}\"".format(name)),
-                sorted(
-                    map(lambda idl_type: idl_type.syntactic_form,
-                        cg_context.union.flattened_member_types)))),
-                 separator=", "),
-        TextNode("};"),
-        TextNode("return ProduceUnionNameInIDL(member_names);"),
-    ])
+    member_type_names = sorted(
+        map(lambda idl_type: idl_type.syntactic_form,
+            cg_context.union.flattened_member_types))
+    body.append(
+        TextNode("return \"({}){}\";".format(
+            " or ".join(member_type_names),
+            "?" if cg_context.union.does_include_nullable_type else "")))
 
     return func_def, None
 

third_party/blink/renderer/platform/bindings/union_base.cc

@@ -4,28 +4,18 @@
 
 #include "third_party/blink/renderer/platform/bindings/union_base.h"
 
-#include "third_party/blink/renderer/platform/wtf/text/string_builder.h"
+#include "third_party/blink/renderer/platform/bindings/exception_messages.h"
+#include "third_party/blink/renderer/platform/bindings/exception_state.h"
 
 namespace blink {
 
 namespace bindings {
 
 // static
-String UnionBase::ProduceUnionNameInIDL(
-    const base::span<const char* const>& member_names) {
-  DCHECK_GE(member_names.size(), 2u);
-
-  StringBuilder builder;
-
-  builder.Append("(");
-  builder.Append(member_names[0]);
-  for (size_t i = 1; i < member_names.size(); ++i) {
-    builder.Append(" or ");
-    builder.Append(member_names[i]);
-  }
-  builder.Append(")");
-
-  return builder.ToString();
+void UnionBase::ThrowTypeErrorNotOfType(ExceptionState& exception_state,
+                                        const char* expected_type) {
+  exception_state.ThrowTypeError(
+      ExceptionMessages::ValueNotOfType(expected_type));
 }
 
 }  // namespace bindings

third_party/blink/renderer/platform/bindings/union_base.h

@@ -13,6 +13,7 @@
 
 namespace blink {
 
+class ExceptionState;
 class ScriptState;
 
 namespace bindings {
@@ -32,8 +33,9 @@ class PLATFORM_EXPORT UnionBase : public GarbageCollected<UnionBase> {
   virtual void Trace(Visitor*) const {}
 
  protected:
-  static String ProduceUnionNameInIDL(
-      const base::span<const char* const>& member_names);
+  // Helper function to reduce the binary size of the generated bindings.
+  static void ThrowTypeErrorNotOfType(ExceptionState& exception_state,
+                                      const char* expected_type);
 
   UnionBase() = default;
 };