do not allow to extend same field twice to prevent the error

[ThePlenkov]

Fixing the issue #1783

In the case if we have a call like this:

Protobuf.Root.fromDescriptor(decodedDescriptorSet);

where decodedDescriptorSet constains files which have same field ( extension + original file ) like in my case validation.proto + google_protobuf.proto ( see the example from the referenced issue ).

[alexander-fenster]

@ThePlenkov Would it be possible to add a unit test for this case? Thank you!

[ThePlenkov]

To test the case you need to but a breakpoint here: https://github.com/protobufjs/protobuf.js/blob/62941d4321824a50d79b7487c1fc1b729002ad0e/src/root.js#L278

Then during comp_import_extend.js test you may see that when we load proto and generate the descriptor - it works fine. But when we load one more root from the descriptor - the issue appears.

Probably the root of the problem is deeper - and the descriptor set should be generated differently - but I have no expertise to comment on that.

[ThePlenkov]

Actually I realized what happens - and is not even related to import. It's only about using fromDescriptor with extended fields. I've used a standard test.proto file for that

[ThePlenkov]

@alexander-fenster hi! Did you have a change to look at unit tests for this problem may be? Thank you!

[ThePlenkov]

Hi! May I ask please what's the reason of this change not going through? Thanks!

[jackkav]

Thanks for the fix @ThePlenkov 🙇

[jackkav]

@alexander-fenster is there anything else blocking this PR review? It is responsible for fixing server reflection.