Revert "Revert "feat: Use an empty frozen hash as default advice""

This reverts commit ed4ceca.

Author: kaylareopelle

metrics_api/lib/opentelemetry/internal/proxy_instrument.rb

@@ -8,7 +8,7 @@ module OpenTelemetry
   module Internal
     # @api private
     class ProxyInstrument
-      def initialize(kind, name, unit, desc, callable, advice = nil)
+      def initialize(kind, name, unit, desc, callable, advice = Metrics::Meter::EMPTY_ADVICE)
         @kind = kind
         @name = name
         @unit = unit

metrics_api/lib/opentelemetry/metrics/meter.rb

@@ -15,6 +15,8 @@ class Meter
       UP_DOWN_COUNTER = Instrument::UpDownCounter.new
       OBSERVABLE_UP_DOWN_COUNTER = Instrument::ObservableUpDownCounter.new
 
+      EMPTY_ADVICE = {}.freeze
+
       NAME_REGEX = /\A[a-zA-Z][-.\w]{0,62}\z/
 
       private_constant(:COUNTER, :OBSERVABLE_COUNTER, :HISTOGRAM, :OBSERVABLE_GAUGE, :UP_DOWN_COUNTER, :OBSERVABLE_UP_DOWN_COUNTER)
@@ -33,7 +35,7 @@ def create_counter(name, unit: nil, description: nil)
         create_instrument(:counter, name, unit, description, nil) { COUNTER }
       end
 
-      def create_histogram(name, unit: nil, description: nil, advice: nil)
+      def create_histogram(name, unit: nil, description: nil, advice: EMPTY_ADVICE)
         create_instrument(:histogram, name, unit, description, nil, advice) { HISTOGRAM }
       end
 
@@ -55,7 +57,7 @@ def create_observable_up_down_counter(name, callback:, unit: nil, description: n
 
       private
 
-      def create_instrument(kind, name, unit, description, callback, advice = nil)
+      def create_instrument(kind, name, unit, description, callback, advice = EMPTY_ADVICE)
         raise InstrumentNameError if name.nil?
         raise InstrumentNameError if name.empty?
         raise InstrumentNameError unless NAME_REGEX.match?(name)

metrics_sdk/lib/opentelemetry/sdk/metrics/instrument/histogram.rb

@@ -10,7 +10,7 @@ module Metrics
       module Instrument
         # {Histogram} is the SDK implementation of {OpenTelemetry::Metrics::Histogram}.
         class Histogram < OpenTelemetry::SDK::Metrics::Instrument::SynchronousInstrument
-          def initialize(name, unit, description, instrumentation_scope, meter_provider, advice = nil)
+          def initialize(name, unit, description, instrumentation_scope, meter_provider, advice = OpenTelemetry::Metrics::Meter::EMPTY_ADVICE)
             @advice = advice
 
             super

metrics_sdk/lib/opentelemetry/sdk/metrics/instrument/synchronous_instrument.rb

@@ -11,7 +11,7 @@ module Instrument
         # {SynchronousInstrument} contains the common functionality shared across
         # the synchronous instruments SDK instruments.
         class SynchronousInstrument
-          def initialize(name, unit, description, instrumentation_scope, meter_provider, advice = nil)
+          def initialize(name, unit, description, instrumentation_scope, meter_provider, advice = OpenTelemetry::Metrics::Meter::EMPTY_ADVICE)
             @name = name
             @unit = unit
             @description = description

metrics_sdk/lib/opentelemetry/sdk/metrics/meter.rb

@@ -33,7 +33,7 @@ def add_metric_reader(metric_reader)
           end
         end
 
-        def create_instrument(kind, name, unit, description, callback, advice = nil)
+        def create_instrument(kind, name, unit, description, callback, advice = OpenTelemetry::Metrics::Meter::EMPTY_ADVICE)
           super do
             case kind
             when :counter then OpenTelemetry::SDK::Metrics::Instrument::Counter.new(name, unit, description, @instrumentation_scope, @meter_provider)

metrics_sdk/test/opentelemetry/sdk/metrics/meter_test.rb

@@ -34,7 +34,7 @@
     it 'does not require advice' do
       instrument = meter.create_histogram('histogram', description: 'stuff', unit: 'things')
 
-      assert_nil instrument.instance_variable_get(:@advice)
+      assert_equal({}, instrument.instance_variable_get(:@advice))
     end
   end