Consider providing a convenient accessor for custom options from Desc* types

[Jayatubi]

It looks like getExtension could only be used on Message instance but not Descriptors as findCustomScalarOption used to do.

What if I want to get the options without creating a new instance but only with the Descriptors, such as get options from an enum?

It would be better if these extension related interfaces could be used with Types, aka Descriptors, instead of instances.

[timostamm]

It is correct that getExtension can only be used on Message instances. A custom option extends one of the option messages defined in descriptor.proto.

For example, a Protobuf enum is described by the message google.protobuf.EnumDescriptorProto, and it has the following field:

message EnumDescriptorProto {
  // ...
  optional EnumOptions options = 3;
  // ...
} 

If you define an enum option, you extend google.protobuf.EnumOptions, and the Protobuf compiler will set the value as an extension on this message field.

You can retrieve the option value again from this message field. Here is how you would do it for an enum:

declare const descEnum: DescEnum;
if (descEnum.proto.options && hasExtension(descEnum.proto.options, my_option)) {
  const myOption = getExtension(descEnum.proto.options, my_option);
  // ...

We have a full tutorial here, which also links to a runnable example.

getExtension is not a direct replacement for findCustomScalarOption. findCustomScalarOption accepts DescEnum as an argument, and looks up proto.options for you, which can be convenient. It would be nice if we had a direct replacement for findCustom*Option that uses extensions under the hood. Let's use this issue to track this addition.

[Jayatubi]

I use protobuf-es not only with the generated types but also with DescriptorSet, from protoc -o. I used to use findCustom*Option with hard coded option number since the previous version of protoc-gen-es skipped all the extensions which were defined in proto files. such as:

const descriptorSet = createDescriptorSet(/* read this file... */);

for (const [name, descriptor] of descriptorSet.messages) {
  if (findCustomScalarOption(descriptor, /* magic number */ 1234567, ScalarType.BOOL)) {
    // Do something with the message which has a specified option
  }
}

It would be better that to keep findCustom*Option not to be deprecated and then replace the hard coded number by generated code from proto file by the new version protoc-gen-es.

[timostamm]

This is implemented for V2 in #828