fix: Coerce aggregation_temporality to symbol

The OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE env var sets the
temporality as a string. However, checks throughout the metrics SDK and
the OTLP exporter expect the temporality to be a symbol.

Now, when aggregations that use this env var are initialized, the
temporality will be coerced into a symbol.

metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram.rb

@@ -26,7 +26,7 @@ def initialize(
             record_min_max: true
           )
             @data_points = {}
-            @aggregation_temporality = aggregation_temporality
+            @aggregation_temporality = aggregation_temporality.to_sym
             @boundaries = boundaries && !boundaries.empty? ? boundaries.sort : nil
             @record_min_max = record_min_max
           end

metrics_sdk/lib/opentelemetry/sdk/metrics/aggregation/sum.rb

@@ -15,7 +15,7 @@ class Sum
 
           def initialize(aggregation_temporality: ENV.fetch('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE', :delta))
             # TODO: the default should be :cumulative, see issue #1555
-            @aggregation_temporality = aggregation_temporality
+            @aggregation_temporality = aggregation_temporality.to_sym
             @data_points = {}
           end
 

metrics_sdk/test/opentelemetry/sdk/metrics/aggregation/explicit_bucket_histogram_test.rb

@@ -21,6 +21,27 @@
   let(:start_time) { (Time.now.to_r * 1_000_000_000).to_i }
   let(:end_time) { ((Time.now + 60).to_r * 1_000_000_000).to_i }
 
+  describe '#initialize' do
+    it 'defaults to the delta aggregation temporality' do
+      exp = OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :delta
+    end
+
+    it 'sets parameters from the environment and converts them to symbols' do
+      exp = OpenTelemetry::TestHelpers.with_env('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE' => 'potato') do
+        OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new
+      end
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :potato
+    end
+
+    it 'prefers explicit parameters rather than the environment and converts them to symbols' do
+      exp = OpenTelemetry::TestHelpers.with_env('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE' => 'potato') do
+        OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new(aggregation_temporality: 'pickles')
+      end
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :pickles
+    end
+  end
+
   describe '#collect' do
     it 'returns all the data points' do
       ebh.update(0, {})

metrics_sdk/test/opentelemetry/sdk/metrics/aggregation/sum_test.rb

@@ -14,6 +14,27 @@
   let(:start_time) { (Time.now.to_r * 1_000_000_000).to_i }
   let(:end_time) { ((Time.now + 60).to_r * 1_000_000_000).to_i }
 
+  describe '#initialize' do
+    it 'defaults to the delta aggregation temporality' do
+      exp = OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :delta
+    end
+
+    it 'sets parameters from the environment and converts them to symbols' do
+      exp = OpenTelemetry::TestHelpers.with_env('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE' => 'potato') do
+        OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new
+      end
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :potato
+    end
+
+    it 'prefers explicit parameters rather than the environment and converts them to symbols' do
+      exp = OpenTelemetry::TestHelpers.with_env('OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE' => 'potato') do
+        OpenTelemetry::SDK::Metrics::Aggregation::ExplicitBucketHistogram.new(aggregation_temporality: 'pickles')
+      end
+      _(exp.instance_variable_get(:@aggregation_temporality)).must_equal :pickles
+    end
+  end
+
   it 'sets the timestamps' do
     sum_aggregation.update(0, {})
     ndp = sum_aggregation.collect(start_time, end_time)[0]