feat: support OTEL_ATTRIBUTE_{COUNT,VALUE_LENGTH}_LIMIT env vars (#1292)

Fixes #1251 by additionally supporting `OTEL_ATTRIBUTE_COUNT_LIMIT` and
`OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT` as ways to configure span limits. As
per spec, the existing model-specific limits (eg: `OTEL_SPAN_ATTRIBUTE_...`
env vars) are preferred when they are present.

The easiest way to do this was to re-use the handy `config_opt` method
in `opentelemetry-common` package, on which we already depend. It made
the lines even longer, which is gross, but it works pretty nicely.

Co-authored-by: Francis Bogsanyi <francis.bogsanyi@shopify.com>

sdk/lib/opentelemetry/sdk/trace/span_limits.rb

@@ -31,13 +31,12 @@ class SpanLimits
         #
         # @return [SpanLimits] with the desired values.
         # @raise [ArgumentError] if any of the max numbers are not positive.
-        def initialize(attribute_count_limit: Integer(ENV.fetch('OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT', 128)), # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
-                       attribute_length_limit: ENV.fetch('OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT',
-                                                         ENV['OTEL_RUBY_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT']),
-                       event_count_limit: Integer(ENV.fetch('OTEL_SPAN_EVENT_COUNT_LIMIT', 128)),
-                       link_count_limit: Integer(ENV.fetch('OTEL_SPAN_LINK_COUNT_LIMIT', 128)),
-                       event_attribute_count_limit: Integer(ENV.fetch('OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT', 128)),
-                       link_attribute_count_limit: Integer(ENV.fetch('OTEL_LINK_ATTRIBUTE_COUNT_LIMIT', 128)))
+        def initialize(attribute_count_limit: Integer(OpenTelemetry::Common::Utilities.config_opt('OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT', 'OTEL_ATTRIBUTE_COUNT_LIMIT', default: 128)), # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+                       attribute_length_limit: OpenTelemetry::Common::Utilities.config_opt('OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT', 'OTEL_RUBY_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT', 'OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT'),
+                       event_count_limit: Integer(OpenTelemetry::Common::Utilities.config_opt('OTEL_SPAN_EVENT_COUNT_LIMIT', default: 128)),
+                       link_count_limit: Integer(OpenTelemetry::Common::Utilities.config_opt('OTEL_SPAN_LINK_COUNT_LIMIT', default: 128)),
+                       event_attribute_count_limit: Integer(OpenTelemetry::Common::Utilities.config_opt('OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT', default: 128)),
+                       link_attribute_count_limit: Integer(OpenTelemetry::Common::Utilities.config_opt('OTEL_LINK_ATTRIBUTE_COUNT_LIMIT', default: 128)))
           raise ArgumentError, 'attribute_count_limit must be positive' unless attribute_count_limit.positive?
           raise ArgumentError, 'attribute_length_limit must not be less than 32' unless attribute_length_limit.nil? || Integer(attribute_length_limit) >= 32
           raise ArgumentError, 'event_count_limit must be positive' unless event_count_limit.positive?

sdk/test/opentelemetry/sdk/trace/span_limits_test.rb

@@ -54,6 +54,7 @@
         _(config.link_attribute_count_limit).must_equal 6
       end
     end
+
     it 'reflects explicit overrides' do
       OpenTelemetry::TestHelpers.with_env('OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT' => '1',
                                           'OTEL_SPAN_EVENT_COUNT_LIMIT' => '2',
@@ -76,5 +77,25 @@
         _(config.attribute_length_limit).must_equal 32
       end
     end
+
+    it 'reflects generic attribute env vars' do
+      OpenTelemetry::TestHelpers.with_env('OTEL_ATTRIBUTE_COUNT_LIMIT' => '1',
+                                          'OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT' => '32') do
+        config = subject.new
+        _(config.attribute_count_limit).must_equal 1
+        _(config.attribute_length_limit).must_equal 32
+      end
+    end
+
+    it 'prefers model-specific attribute env vars over generic attribute env vars' do
+      OpenTelemetry::TestHelpers.with_env('OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT' => '1',
+                                          'OTEL_ATTRIBUTE_COUNT_LIMIT' => '2',
+                                          'OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT' => '32',
+                                          'OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT' => '33') do
+        config = subject.new
+        _(config.attribute_count_limit).must_equal 1
+        _(config.attribute_length_limit).must_equal 32
+      end
+    end
   end
 end