Allow users to hide Gen X columns

src/BenchmarkDotNet/Attributes/MemoryDiagnoserAttribute.cs

@@ -9,9 +9,10 @@ public class MemoryDiagnoserAttribute : Attribute, IConfigSource
     {
         public IConfig Config { get; }
 
-        public MemoryDiagnoserAttribute()
+        /// <param name="displayGenColumns">Display Garbage Collections per Generation columns (Gen 0, Gen 1, Gen 2). True by default.</param>
+        public MemoryDiagnoserAttribute(bool displayGenColumns = true)
         {
-            Config = ManualConfig.CreateEmpty().AddDiagnoser(MemoryDiagnoser.Default);
+            Config = ManualConfig.CreateEmpty().AddDiagnoser(new MemoryDiagnoser(new MemoryDiagnoserConfig(displayGenColumns)));
         }
     }
 }

src/BenchmarkDotNet/Configs/ImmutableConfig.cs

@@ -92,7 +92,7 @@ public sealed class ImmutableConfig : IConfig
         public IAnalyser GetCompositeAnalyser() => new CompositeAnalyser(analysers);
         public IDiagnoser GetCompositeDiagnoser() => new CompositeDiagnoser(diagnosers);
 
-        public bool HasMemoryDiagnoser() => diagnosers.Contains(MemoryDiagnoser.Default);
+        public bool HasMemoryDiagnoser() => diagnosers.OfType<MemoryDiagnoser>().Any();
 
         public bool HasThreadingDiagnoser() => diagnosers.Contains(ThreadingDiagnoser.Default);
 

src/BenchmarkDotNet/Diagnosers/MemoryDiagnoser.cs

@@ -15,9 +15,11 @@ public class MemoryDiagnoser : IDiagnoser
     {
         private const string DiagnoserId = nameof(MemoryDiagnoser);
 
-        public static readonly MemoryDiagnoser Default = new MemoryDiagnoser();
+        public static readonly MemoryDiagnoser Default = new MemoryDiagnoser(new MemoryDiagnoserConfig(displayGenColumns: true));
 
-        private MemoryDiagnoser() { } // we want to have only a single instance of MemoryDiagnoser
+        public MemoryDiagnoser(MemoryDiagnoserConfig config) => Config = config;
+
+        public MemoryDiagnoserConfig Config { get; }
 
         public RunMode GetRunMode(BenchmarkCase benchmarkCase) => RunMode.NoOverhead;
 
@@ -33,9 +35,13 @@ public class MemoryDiagnoser : IDiagnoser
 
         public IEnumerable<Metric> ProcessResults(DiagnoserResults diagnoserResults)
         {
-            yield return new Metric(GarbageCollectionsMetricDescriptor.Gen0, diagnoserResults.GcStats.Gen0Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
-            yield return new Metric(GarbageCollectionsMetricDescriptor.Gen1, diagnoserResults.GcStats.Gen1Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
-            yield return new Metric(GarbageCollectionsMetricDescriptor.Gen2, diagnoserResults.GcStats.Gen2Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
+            if (diagnoserResults.GcStats.Gen0Collections > 0 && Config.DisplayGenColumns)
+                yield return new Metric(GarbageCollectionsMetricDescriptor.Gen0, diagnoserResults.GcStats.Gen0Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
+            if (diagnoserResults.GcStats.Gen1Collections > 0 && Config.DisplayGenColumns)
+                yield return new Metric(GarbageCollectionsMetricDescriptor.Gen1, diagnoserResults.GcStats.Gen1Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
+            if (diagnoserResults.GcStats.Gen2Collections > 0 && Config.DisplayGenColumns)
+                yield return new Metric(GarbageCollectionsMetricDescriptor.Gen2, diagnoserResults.GcStats.Gen2Collections / (double)diagnoserResults.GcStats.TotalOperations * 1000);
+
             yield return new Metric(AllocatedMemoryMetricDescriptor.Instance, diagnoserResults.GcStats.BytesAllocatedPerOperation);
         }
 

src/BenchmarkDotNet/Diagnosers/MemoryDiagnoserConfig.cs

@@ -0,0 +1,16 @@
+using JetBrains.Annotations;
+
+namespace BenchmarkDotNet.Diagnosers
+{
+    public class MemoryDiagnoserConfig
+    {
+        /// <param name="displayGenColumns">Display Garbage Collections per Generation columns (Gen 0, Gen 1, Gen 2). True by default.</param>
+        [PublicAPI]
+        public MemoryDiagnoserConfig(bool displayGenColumns = true)
+        {
+            DisplayGenColumns = displayGenColumns;
+        }
+
+        public bool DisplayGenColumns { get; }
+    }
+}