Allow loading grpc/errors.rb before grpc.rb

[blowmage]

As you know, the Ruby gem loads the compiled gRPC library and initializes all system resources when the following is called in a Ruby file:

require 'grpc'

Once the compiled gRPC library is loaded the Ruby process cannot be forked, so it is very common for Ruby apps to delay requiring GRPC until right before it is needed. (See #8798) However, it would be very beneficial for Ruby apps to be able to reference some GRPC code structures before the compiled gRPC library is loaded. For instance, it would be beneficial to be able to register error handlers.

This PR makes a couple small changes. First, it removes the require_relative './grpc' from grpc/errors.rb, allowing the error classes to be loaded before the compiled gRPC library. Now the grpc/errors.rb file behaves the same as the grpc/logconfig.rb file, where require 'grpc/logconfig' can be called before require 'grpc' which loads the compiled gRPC library.

Second, it adds the file grpc/status_codes.rb that defines GPRC::StatusCodes to the gem. GPRC::StatusCodes is the same structure as GPRC::Core::StatusCodes, but the latter is defined in the compiled gRPC library, and therefore can't be used. So GPRC::StatusCodes has been added that defines the same values, with documentation, so it can also be documented as part of the public API. The grpc/errors.rb file now depends on this new grpc/status_codes.rb file.

These changes allow errors to be loaded before the compiled gRPC library and is backwards compatible to previous releases.

[apolcyn]

I'm thinking we can still save the benefits of this change, but without adding the second clone module.

Is it possible to just move the status code definitions in the C extension to this pure ruby file, but keep all of the constants under the same module?

I.e., I'm thinking we could delete this function: https://github.com/grpc/grpc/blob/master/src/ruby/ext/grpc/rb_grpc.c#L158, and then have the new ruby file put the codes under GRPC::Core

Also, can we add a test script to illustrate this; we could probably have a small test script under https://github.com/grpc/grpc/tree/master/src/ruby/end2end, and add it to the list of test scripts invoked from https://github.com/grpc/grpc/blob/master/tools/run_tests/helper_scripts/run_ruby_end2end_tests.sh (these tests are meant to do things that are cleaner ran in their own process).

[blowmage]

I'm thinking we can still save the benefits of this change, but without adding the second clone module.

Funny enough, using StatusCodes before the compiled gRPC library is loaded was my next requested change. We would love to be able to reference those constants.

Is it possible to just move the status code definitions in the C extension to this pure ruby file, but keep all of the constants under the same module?

Yes, that should be possible. I wanted this PR to be as additive as possible, so I didn't want to mess with that existing code. Would you like me to make that change in this PR?

[apolcyn]

Yes, that should be possible. I wanted this PR to be as additive as possible, so I didn't want to mess with that existing code. Would you like me to make that change in this PR?

Yes please, I'd prefer to do this one as an atomic change.

[blowmage]

@apolcyn I think i fixed the copyright problem. Can you restart Kokoro?

[blowmage]

Are those Kokoro failures due to the changes made in this PR?

[blowmage]

@apolcyn The tools scripts that failed on Kokoro pass for me locally. Do you understand why it failed? Should I rebase this PR on latest master?

[blowmage]

Now that I've fixed the copyright failure, should these new files all use 2019?

[apolcyn]

Those errors look unrelated to this change, no need ot rebase

[apolcyn]

@blowmage before merging, can you please squash down the commits into one, e.g. with a git rebase ?

[blowmage]

Squashed.

[apolcyn]

node macos: #19422
objc examples: #19925

[apolcyn]

C/C++ macos: #19819

[blowmage]

@apolcyn Thanks for accepting! This will be released in 1.24.0, right? It isn't going to make it for the upcoming 1.23.0 release?

[apolcyn]

Yes, this will be in the 1.24.0 release. And right, the 1.23.0 branch has been cut (we don't tend to backport larger changes like this).

[blowmage]

K, I was playing with this some more and it looks like Struct::Status is still being defined in grpc_c. I will submit another PR to define that class in Ruby, and add more test coverage to the end2end scripts. But before I create that PR I would like to get some feedback on #19931.