WhenMethodFilter - Support dynamic filtering using lambda

src/NLog/Filters/WhenMethodFilter.cs

@@ -0,0 +1,61 @@
+// 
+// Copyright (c) 2004-2019 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without 
+// modification, are permitted provided that the following conditions 
+// are met:
+// 
+// * Redistributions of source code must retain the above copyright notice, 
+//   this list of conditions and the following disclaimer. 
+// 
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution. 
+// 
+// * Neither the name of Jaroslaw Kowalski nor the names of its 
+//   contributors may be used to endorse or promote products derived from this
+//   software without specific prior written permission. 
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
+// THE POSSIBILITY OF SUCH DAMAGE.
+// 
+
+namespace NLog.Filters
+{
+    using System;
+
+    /// <summary>
+    /// Matches the provided filter-method
+    /// </summary>
+    public class WhenMethodFilter : Filter
+    {
+        private readonly Func<LogEventInfo, FilterResult> _filterMethod;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WhenMethodFilter" /> class.
+        /// </summary>
+        public WhenMethodFilter(Func<LogEventInfo, FilterResult> filterMethod)
+        {
+            if (filterMethod == null)
+                throw new ArgumentNullException(nameof(filterMethod));
+            _filterMethod = filterMethod;
+        }
+
+        /// <inheritdoc/>
+        protected override FilterResult Check(LogEventInfo logEvent)
+        {
+            return _filterMethod(logEvent);
+        }
+    }
+}

src/NLog/Filters/WhenRepeatedFilter.cs

@@ -120,7 +120,7 @@ public class WhenRepeatedFilter : LayoutBasedFilter
         private readonly Stack<KeyValuePair<FilterInfoKey, FilterInfo>> _objectPool = new Stack<KeyValuePair<FilterInfoKey, FilterInfo>>(1000);
 
         /// <summary>
-        /// Constructor
+        /// Initializes a new instance of the <see cref="WhenRepeatedFilter" /> class.
         /// </summary>
         public WhenRepeatedFilter()
         {

tests/NLog.UnitTests/Filters/APITests.cs

@@ -31,10 +31,10 @@
 // THE POSSIBILITY OF SUCH DAMAGE.
 // 
 
-using NLog.Config;
-
 namespace NLog.UnitTests.Filters
 {
+    using System.Linq;
+    using NLog.Config;
     using NLog.Layouts;
     using NLog.Filters;
     using Xunit;
@@ -65,5 +65,27 @@ public void APITest()
             Assert.Equal("zzz", wcf.Substring);
             Assert.Equal(FilterResult.Ignore, wcf.Action);
         }
+
+        [Fact]
+        public void WhenMethodFilterApiTest()
+        {
+            // Stage
+            var logFactory = new LogFactory();
+            var logger1 = logFactory.GetLogger("Hello");
+            var logger2 = logFactory.GetLogger("Goodbye");
+            var config = new LoggingConfiguration(logFactory);
+            var target = new NLog.Targets.DebugTarget() { Layout = "${message}" };
+            config.AddRuleForAllLevels(target);
+            config.LoggingRules.Last().Filters.Add(new WhenMethodFilter((l) => l.LoggerName == logger1.Name ? FilterResult.Ignore : FilterResult.Neutral));
+            logFactory.Configuration = config;
+
+            // Act 1
+            logger1.Info("Hello World");
+            Assert.Empty(target.LastMessage);
+
+            // Act 2
+            logger2.Info("Goodbye World");
+            Assert.Equal("Goodbye World", target.LastMessage);
+        }
     }
 }