Remove span_type method call on SpanOperation

[TonyCTHsu]

Closes #4762

Why

Datadog tracer is removing a deprecated method span_type for dd-trace-rb 2+ . This is the PR.

What

• Change the tracing implementation in graphql-ruby from span_type to type.
• Remove constant reference from dd-trace-rb
• Deprecate service option and its default
• Deprecate tracer option

Additional Notes

The test is setup with DataDog/dd-trace-rb#3376

🚨 This change is backward compatible (All graphql-ruby versions works with dd-trace-rb 1+ ). However, graphql-ruby users need to upgrade with this change to use dd-trace-rb 2+.

[rmosolgo]

Just to make sure I understand:

What will dd-trace-rb do with this type: 'custom' argument? Will it ignore it, or 💥 ?

If this code only works with dd-trace-rb 2+, what do you think about adding a version check of some kind in def initialize above? If that's possible, it might be a nicer development experience than troubleshooting the argument error (if span: ... does cause an error, that is).

[TonyCTHsu]

What will dd-trace-rb do with this type: 'custom' argument?

The data model of Span/SpanOperation contains a type field, which can filled by multiple ways.

1. Through Tracing#trace(...), there are both type/span_type as optional keyword arguments. https://github.com/DataDog/dd-trace-rb/blob/master/lib/datadog/tracing/tracer.rb#L131-L132

Both options yields the same outcome.

[2] pry(main)> span = Datadog::Tracing.trace('my_span', span_type: 'custom');
[3] pry(main)> span.type
=> "custom"

[4] pry(main)> span = Datadog::Tracing.trace('my_span', type: 'custom');
[5] pry(main)> span.type
=> "custom"

2. Through attribute setter from the SpanOperation, https://github.com/DataDog/dd-trace-rb/blob/master/lib/datadog/tracing/span_operation.rb#L502
   Since, span_type= is just an alias for type=, the following code are the same.

[3] pry(main)> Datadog::Tracing.trace('my_span') do |span|
[3] pry(main)*   span.span_type = 'custom'
[3] pry(main)*   puts span.type
[3] pry(main)* end
custom

[3] pry(main)> Datadog::Tracing.trace('my_span') do |span|
[3] pry(main)*   span.type = 'custom'
[3] pry(main)*   puts span.type
[3] pry(main)* end
custom

If this code only works with dd-trace-rb 2+

This is not entirely correct. Because the changes basically migrate the deprecated usage to a supported usage, it works on all dd-trace-rb versions.

• dd-trace-rb 1.x supports both span_type= and type=
• dd-trace-rb 2.x only supports type=

The existing graphql-ruby versions without such changes won't work with dd-trace-rb 2+. That is why graphql-ruby users need to upgrade with this change to use dd-trace-rb 2+.