v8binding: Fix use of zero-length variable length arrays

Fix the bindings generator so that it won't use variable length
arrays with zero sizes, which are forbidden by C++ standard.

Bug: 932489
Change-Id: Ife08fe8be4e6b9907c3c97c8047c0432cdddd4bc
Reviewed-on: https://chromium-review.googlesource.com/c/1490985
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636796}

third_party/blink/renderer/bindings/templates/callback_invoke.cc.tmpl

@@ -192,13 +192,18 @@
   {% set has_variadic_argument = arguments[-1].is_variadic %}
   {% set non_variadic_arguments = arguments | rejectattr('is_variadic') | list %}
   {% set variadic_argument = arguments[-1] if has_variadic_argument else None %}
-  {% set arguments_length = '%d + %s.size()' % (non_variadic_arguments|length, variadic_argument.name) if has_variadic_argument else non_variadic_arguments|length %}
   {% for argument in non_variadic_arguments %}
   v8::Local<v8::Value> {{argument.v8_name}} = {{argument.cpp_value_to_v8_value}};
   {% endfor %}
   {% if has_variadic_argument %}
-  const int argc = {{arguments_length}};
-  v8::Local<v8::Value> argv[argc];
+  // Secure one element at least in |argv| to avoid the following restriction.
+  //
+  // C++14 8.3.4 Arrays
+  // If the constant-expression (5.19) is present, it shall be a converted
+  // constant expression of type std::size_t and its value shall be greater than
+  // zero.
+  const int argc = {{non_variadic_arguments|length}} + {{variadic_argument.name}}.size();
+  v8::Local<v8::Value> argv[std::max(1, argc)];
   {% for argument in non_variadic_arguments %}
   argv[{{loop.index0}}] = {{argument.v8_name}};
   {% endfor %}
@@ -206,7 +211,7 @@
     argv[{{non_variadic_arguments|length}} + i] = ToV8({{variadic_argument.name}}[i], argument_creation_context, GetIsolate());
   }
   {% else %}{# if has_variadic_argument #}
-  constexpr int argc = {{arguments_length}};
+  constexpr int argc = {{non_variadic_arguments|length}};
   v8::Local<v8::Value> argv[] = { {{non_variadic_arguments | join(', ', 'v8_name')}} };
   static_assert(static_cast<size_t>(argc) == base::size(argv), "size mismatch");
   {% endif %}

third_party/blink/renderer/bindings/tests/results/core/v8_any_callback_function_variadic_any_args.cc

@@ -84,8 +84,14 @@ v8::Maybe<ScriptValue> V8AnyCallbackFunctionVariadicAnyArgs::Invoke(bindings::V8
   v8::Local<v8::Object> argument_creation_context =
       callback_relevant_script_state->GetContext()->Global();
   ALLOW_UNUSED_LOCAL(argument_creation_context);
+  // Secure one element at least in |argv| to avoid the following restriction.
+  //
+  // C++14 8.3.4 Arrays
+  // If the constant-expression (5.19) is present, it shall be a converted
+  // constant expression of type std::size_t and its value shall be greater than
+  // zero.
   const int argc = 0 + arguments.size();
-  v8::Local<v8::Value> argv[argc];
+  v8::Local<v8::Value> argv[std::max(1, argc)];
   for (wtf_size_t i = 0; i < arguments.size(); ++i) {
     argv[0 + i] = ToV8(arguments[i], argument_creation_context, GetIsolate());
   }
@@ -185,8 +191,14 @@ v8::Maybe<ScriptValue> V8AnyCallbackFunctionVariadicAnyArgs::Construct(const Vec
   v8::Local<v8::Object> argument_creation_context =
       callback_relevant_script_state->GetContext()->Global();
   ALLOW_UNUSED_LOCAL(argument_creation_context);
+  // Secure one element at least in |argv| to avoid the following restriction.
+  //
+  // C++14 8.3.4 Arrays
+  // If the constant-expression (5.19) is present, it shall be a converted
+  // constant expression of type std::size_t and its value shall be greater than
+  // zero.
   const int argc = 0 + arguments.size();
-  v8::Local<v8::Value> argv[argc];
+  v8::Local<v8::Value> argv[std::max(1, argc)];
   for (wtf_size_t i = 0; i < arguments.size(); ++i) {
     argv[0 + i] = ToV8(arguments[i], argument_creation_context, GetIsolate());
   }