Do not apply ExplicitBucketHistogramConfiguration to non-histograms (#3126)

Author: alanwest

src/OpenTelemetry/CHANGELOG.md

@@ -2,6 +2,12 @@
 
 ## Unreleased
 
+* Fix issue where `ExplicitBucketHistogramConfiguration` could be used to
+  configure metric streams for instruments that are not histograms. Currently,
+  it is not possible to change the aggregation of an instrument with views. This
+  may be possible in the future.
+  ([#3126](https://github.com/open-telemetry/opentelemetry-dotnet/pull/3126))
+
 ## 1.2.0-rc4
 
 Released 2022-Mar-30

src/OpenTelemetry/Metrics/MeterProviderSdk.cs

@@ -162,6 +162,18 @@ internal MeterProviderSdk(
                             try
                             {
                                 metricStreamConfig = viewConfig(instrument);
+
+                                if (metricStreamConfig is ExplicitBucketHistogramConfiguration
+                                    && instrument.GetType().GetGenericTypeDefinition() != typeof(Histogram<>))
+                                {
+                                    metricStreamConfig = null;
+
+                                    OpenTelemetrySdkEventSource.Log.MetricViewIgnored(
+                                        instrument.Name,
+                                        instrument.Meter.Name,
+                                        "The current SDK does not allow aggregating non-Histogram instruments as Histograms.",
+                                        "Fix the view configuration.");
+                                }
                             }
                             catch (Exception ex)
                             {

test/OpenTelemetry.Tests/Metrics/MetricViewTests.cs

@@ -457,6 +457,37 @@ public void ViewToProduceMultipleStreamsWithDuplicatesFromInstrument()
             Assert.Equal("renamedStream2", exportedItems[1].Name);
         }
 
+        [Fact]
+        public void ViewWithHistogramConfiguraionIgnoredWhenAppliedToNonHistogram()
+        {
+            using var meter = new Meter(Utils.GetCurrentMethodName());
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddMeter(meter.Name)
+                .AddView("NotAHistogram", new ExplicitBucketHistogramConfiguration() { Name = "ImAHistogram" })
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            var counter = meter.CreateCounter<long>("NotAHistogram");
+            counter.Add(10);
+            meterProvider.ForceFlush(MaxTimeToAllowForFlush);
+
+            Assert.Single(exportedItems);
+            var metric = exportedItems[0];
+
+            Assert.Equal("NotAHistogram", metric.Name);
+
+            List<MetricPoint> metricPoints = new List<MetricPoint>();
+            foreach (ref readonly var mp in metric.GetMetricPoints())
+            {
+                metricPoints.Add(mp);
+            }
+
+            Assert.Single(metricPoints);
+            var metricPoint = metricPoints[0];
+            Assert.Equal(10, metricPoint.GetSumLong());
+        }
+
         [Fact]
         public void ViewToProduceCustomHistogramBound()
         {