[PROF-7145] Remove support for profiling Ruby 2.2

[ivoanjo]

What does this PR do?:

This PR removes support for profiling Ruby 2.2 using the Continuous Profiling product. Other products shipped in ddtrace (tracing, application security monitoring, CI, etc) are unaffected.

This dropping of support does not impact our customer's ability to install the latest dd-trace-rb on Ruby 2.2. What it does is

1. Skip compilation of the profiling native extension on Ruby 2.2
2. Print a warning message when customers try to enable profiling on Ruby 2.2 (but does not otherwise block or break their application)

The warning message shown to customers is:

W, [2023-02-01T11:42:57.022293 #410738] WARN -- ddtrace: [ddtrace] Profiling was requested but is not supported, profiling disabled: Your ddtrace installation is missing support for the Continuous Profiler because the profiler only supports Ruby 2.3 or newer. Upgrade to a modern Ruby to enable profiling for your app.

(This PR is similar to #2140 where we dropped support for Ruby 2.1)

Motivation:

There is little customer interest on profiling Ruby 2.2, and supporting old Rubies also comes with an extra tax -- just look how much code and complexity is being removed by this PR.

Additional Notes:

(N/A)

How to test the change?:

• Validate that test suite still runs successfully on Ruby 2.2
• Validate that you get the above error message when trying to profile a Ruby 2.2 application

[lloeki]

LGTM!

[lloeki]

Wondering if we should have a helper or two to do these kind of checks instead of ad-hoc winging the checks each time.

This would also make such calls log-able/trackable/grep-able.

[ivoanjo]

I would usually say yes, but given that's additional work done just for the benefit of Ruby 2.1 and 2.2, in this very specific case I don't think it's work the extra effort.

[lloeki]

Here's another ad-hoc pattern.

[ivoanjo]

This pattern shows up in the codebase 3 times:

Searching 2551 files for "RUBY_VERSION.start_with?('2.1.', '2.2.')" (case sensitive)

~/datadog/second-dd-trace-rb/ext/ddtrace_profiling_native_extension/native_extension_helpers.rb:
  267            )
  268  
  269:           ruby_version_not_supported if RUBY_VERSION.start_with?('2.1.', '2.2.')
  270          end
  271  

~/datadog/second-dd-trace-rb/integration/images/include/build_ddtrace_profiling_native_extension.rb:
    2  
    3  if local_gem_path = ENV['DD_DEMO_ENV_GEM_LOCAL_DDTRACE']
    4:   if RUBY_VERSION.start_with?('2.1.', '2.2.')
    5      puts "\n== Skipping build of profiler native extension on Ruby 2.1/2.2 =="
    6    else

~/datadog/second-dd-trace-rb/spec/datadog/profiling/spec_helper.rb:
   35      testcase.skip('Profiling is not supported on JRuby') if PlatformHelpers.jruby?
   36      testcase.skip('Profiling is not supported on TruffleRuby') if PlatformHelpers.truffleruby?
   37:     testcase.skip('Profiling is not supported on Ruby 2.1/2.2') if RUBY_VERSION.start_with?('2.1.', '2.2.')
   38  
   39      # Profiling is not officially supported on macOS due to missing libdatadog binaries,

3 matches across 3 files

...but actually only shows up once in the code shipped to customers.

I'm somewhat hesitant in introducing additional complexity to avoid having duplication in test/scaffolding code, so I'm leaving towards keeping it as-is.

[codecov-commenter]

Codecov Report

Merging #2592 (6b1f5ce) into master (4a1050c) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2592      +/-   ##
==========================================
- Coverage   98.04%   98.04%   -0.01%     
==========================================
  Files        1143     1143              
  Lines       62031    62017      -14     
  Branches     2801     2789      -12     
==========================================
- Hits        60821    60807      -14     
  Misses       1210     1210              

Impacted Files	Coverage Δ
lib/datadog/profiling/stack_recorder.rb	76.66% <ø> (-1.46%)	⬇️
...dog/profiling/collectors/cpu_and_wall_time_spec.rb	97.88% <ø> (-0.02%)	⬇️
...filing/collectors/cpu_and_wall_time_worker_spec.rb	94.71% <ø> (-0.04%)	⬇️
spec/datadog/profiling/http_transport_spec.rb	99.56% <ø> (+0.42%)	⬆️
spec/datadog/profiling/native_extension_spec.rb	98.72% <ø> (-0.02%)	⬇️
...iling_native_extension/native_extension_helpers.rb	96.73% <100.00%> (ø)
...g/profiling/collectors/cpu_and_wall_time_worker.rb	100.00% <100.00%> (ø)
...tadog/profiling/collectors/idle_sampling_helper.rb	93.54% <100.00%> (ø)
lib/datadog/profiling/collectors/old_stack.rb	100.00% <100.00%> (ø)
...pec/datadog/profiling/collectors/old_stack_spec.rb	97.47% <100.00%> (-0.03%)	⬇️
... and 7 more

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[ivoanjo]

Thanks Loic for the review!

One of the system tests is shown as failing, but we're investigating it separately, as it happens with master as well and we don't expect it to be related to this change.

Merging away!