v8: warn in Template::Set() on improper use

The next major release will make it a fatal error to use non-primitive
values in function templates and object templates.

Print a warning that includes the C and JS stack trace to tell people to
upgrade their add-ons.  The C stack trace is only printed on platforms
that support it (the BSDs, OS X and Linux+glibc.)

The warning can be disabled with the new `--nowarn_template_set` flag.

Refs: nodejs#6216
PR-URL: nodejs#6277
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: bnoordhuis

deps/v8/src/api.cc

@@ -1031,6 +1031,16 @@ void Template::Set(v8::Local<Name> name, v8::Local<Data> value,
       i::Handle<i::FunctionTemplateInfo>::cast(templ)->set_do_not_cache(true);
     }
   }
+  if (i::FLAG_warn_template_set &&
+      value_obj->IsJSReceiver() &&
+      !value_obj->IsTemplateInfo()) {
+    base::OS::PrintError(
+        "(node) v8::%sTemplate::Set() with non-primitive values is deprecated\n"
+        "(node) and will stop working in the next major release.\n",
+        templ->IsFunctionTemplateInfo() ? "Function" : "Object");
+    isolate->PrintStack(stderr, i::Isolate::kPrintStackConcise);
+    base::DumpBacktrace();
+  }
   i::ApiNatives::AddDataProperty(isolate, templ, Utils::OpenHandle(*name),
                                  value_obj,
                                  static_cast<i::PropertyAttributes>(attribute));

deps/v8/src/flag-definitions.h

@@ -172,6 +172,9 @@ struct MaybeBoolFlag {
 //
 #define FLAG FLAG_FULL
 
+DEFINE_BOOL(warn_template_set, true,
+            "warn on deprecated v8::Template::Set() use")
+
 DEFINE_BOOL(experimental_extras, false,
             "enable code compiled in via v8_experimental_extra_library_files")