feat: Gauge metrics exporter encoding

exporter/otlp-metrics/lib/opentelemetry/exporter/otlp/metrics/metrics_exporter.rb

@@ -214,18 +214,17 @@ def encode(metrics_data)
           end
 
           # metrics_pb has following type of data: :gauge, :sum, :histogram, :exponential_histogram, :summary
-          # current metric sdk only implements instrument: :counter -> :sum, :histogram -> :histogram
+          # current metric sdk only implements instrument: :counter -> :sum, :histogram -> :histogram, :gauge -> :gauge
           #
           # metrics [MetricData]
           def as_otlp_metrics(metrics)
             case metrics.instrument_kind
-            when :observable_gauge
+            when :observable_gauge, :gauge
               Opentelemetry::Proto::Metrics::V1::Metric.new(
                 name: metrics.name,
                 description: metrics.description,
                 unit: metrics.unit,
                 gauge: Opentelemetry::Proto::Metrics::V1::Gauge.new(
-                  aggregation_temporality: as_otlp_aggregation_temporality(metrics.aggregation_temporality),
                   data_points: metrics.data_points.map do |ndp|
                     number_data_point(ndp)
                   end

exporter/otlp-metrics/test/opentelemetry/exporter/otlp/metrics/metrics_exporter_test.rb

@@ -576,11 +576,16 @@
       stub_request(:post, 'http://localhost:4318/v1/metrics').to_return(status: 200)
       meter_provider.add_metric_reader(exporter)
       meter   = meter_provider.meter('test')
+
       counter = meter.create_counter('test_counter', unit: 'smidgen', description: 'a small amount of something')
       counter.add(5, attributes: { 'foo' => 'bar' })
 
       histogram = meter.create_histogram('test_histogram', unit: 'smidgen', description: 'a small amount of something')
       histogram.record(10, attributes: { 'oof' => 'rab' })
+
+      gauge = meter.create_gauge('test_gauge', unit: 'smidgen', description: 'a small amount of something')
+      gauge.record(15, attributes: { 'baz' => 'qux' })
+
       exporter.pull
       meter_provider.shutdown
 
@@ -644,6 +649,24 @@
                         ],
                         aggregation_temporality: Opentelemetry::Proto::Metrics::V1::AggregationTemporality::AGGREGATION_TEMPORALITY_DELTA
                       )
+                    ),
+                    Opentelemetry::Proto::Metrics::V1::Metric.new(
+                      name: 'test_gauge',
+                      description: 'a small amount of something',
+                      unit: 'smidgen',
+                      gauge: Opentelemetry::Proto::Metrics::V1::Gauge.new(
+                        data_points: [
+                          Opentelemetry::Proto::Metrics::V1::NumberDataPoint.new(
+                            attributes: [
+                              Opentelemetry::Proto::Common::V1::KeyValue.new(key: 'baz', value: Opentelemetry::Proto::Common::V1::AnyValue.new(string_value: 'qux'))
+                            ],
+                            as_int: 15,
+                            start_time_unix_nano: 1_699_593_427_329_946_585,
+                            time_unix_nano: 1_699_593_427_329_946_586,
+                            exemplars: nil
+                          )
+                        ]
+                      )
                     )
                   ]
                 )

exporter/otlp-metrics/test/test_helper.rb

@@ -26,6 +26,7 @@ def collect(start_time, end_time, data_points)
 
 OpenTelemetry::SDK::Metrics::Aggregation::Sum.prepend(MockSum)
 OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.prepend(MockSum)
+OpenTelemetry::SDK::Metrics::Aggregation::LastValue.prepend(MockSum)
 
 def create_metrics_data(name: '', description: '', unit: '', instrument_kind: :counter, resource: nil,
                         instrumentation_scope: OpenTelemetry::SDK::InstrumentationScope.new('', 'v0.0.1'),