NLog · snakefoot · Jun 20, 2022 · Jun 20, 2022
diff --git a/src/NLog/LayoutRenderers/ApplicationEnvironment/AssemblyVersionLayoutRenderer.cs b/src/NLog/LayoutRenderers/ApplicationEnvironment/AssemblyVersionLayoutRenderer.cs
@@ -52,14 +52,6 @@ namespace NLog.LayoutRenderers
    [ThreadAgnostic]
    public class AssemblyVersionLayoutRenderer : LayoutRenderer
    {
-        /// <summary>
-        /// Initializes a new instance of the <see cref="AssemblyVersionLayoutRenderer" /> class.
-        /// </summary>
-        public AssemblyVersionLayoutRenderer()
-        {
-            _format = DefaultFormat;
-        }
-
        /// <summary>
        /// The (full) name of the assembly. If <c>null</c>, using the entry assembly.
        /// </summary>
@@ -77,9 +69,12 @@ public AssemblyVersionLayoutRenderer()
        /// <docgen category='Layout Options' order='10' />
        public AssemblyVersionType Type { get; set; } = AssemblyVersionType.Assembly;

-        private const string DefaultFormat = "major.minor.build.revision";
-
-        private string _format;
+        ///<summary>
+        /// The default value to render if the Version is not available
+        ///</summary>
+        /// <docgen category='Layout Options' order='10' />
+        public string Default { get => _default ?? GenerateDefaultValue(); set => _default = value; }
+        private string _default;

        /// <summary>
        /// Gets or sets the custom format of the assembly version output.
@@ -94,8 +89,11 @@ public AssemblyVersionLayoutRenderer()
        public string Format
        {
            get => _format;
-            set => _format = value?.ToLowerInvariant();
+            set => _format = value?.ToLowerInvariant() ?? string.Empty;
        }
+        private string _format = DefaultFormat;
+
+        private const string DefaultFormat = "major.minor.build.revision";

        /// <inheritdoc/>
        protected override void InitializeLayoutRenderer()
@@ -117,17 +115,26 @@ protected override void CloseLayoutRenderer()
        protected override void Append(StringBuilder builder, LogEventInfo logEvent)
        {
            var version = _assemblyVersion ?? (_assemblyVersion = ApplyFormatToVersion(GetVersion()));
-
-            if (string.IsNullOrEmpty(version))
-            {
-                version = $"Could not find value for {(string.IsNullOrEmpty(Name) ? "entry" : Name)} assembly and version type {Type}";
-            }
-
+            if (version is null)
+                version = GenerateDefaultValue();
            builder.Append(version);
        }

        private string ApplyFormatToVersion(string version)
        {
+            if (version is null)
+            {
+                return _default;
+            }
+            else if (StringHelpers.IsNullOrWhiteSpace(version))
+            {
+                return _default ?? GenerateDefaultValue();
+            }
+            else if (version == "0.0.0.0" && _default != null)
+            {
+                return _default;
+            }
+
            if (Format.Equals(DefaultFormat, StringComparison.OrdinalIgnoreCase) || string.IsNullOrEmpty(version))
            {
                return version;
@@ -142,6 +149,11 @@ private string ApplyFormatToVersion(string version)
            return version;
        }

+        private string GenerateDefaultValue()
+        {
+            return $"Could not find value for {(string.IsNullOrEmpty(Name) ? "entry" : Name)} assembly and version type {Type}";
+        }
+
 #if NETSTANDARD1_3

        private string GetVersion()
@@ -166,8 +178,18 @@ private System.Reflection.Assembly GetAssembly()

        private string GetVersion()
        {
-            var assembly = GetAssembly();
-            return GetVersion(assembly);
+            try
+            {
+                var assembly = GetAssembly();
+                return GetVersion(assembly) ?? string.Empty;
+            }
+            catch (Exception ex)
+            {
+                NLog.Common.InternalLogger.Warn(ex, "${assembly-version} - Failed to load assembly {0}", Name);
+                if (ex.MustBeRethrown())
+                    throw;
+                return null;
+            }
        }

        /// <summary>

diff --git a/src/NLog/LayoutRenderers/ApplicationEnvironment/AssemblyVersionType.cs b/src/NLog/LayoutRenderers/ApplicationEnvironment/AssemblyVersionType.cs
@@ -49,7 +49,7 @@ public enum AssemblyVersionType
        File,

        /// <summary>
-        /// Gets additional version information.
+        /// Gets the product version, extracted from the additional version information.
        /// </summary>
        Informational
    }

diff --git a/tests/NLog.UnitTests/LayoutRenderers/ApplicationEnvironment/AssemblyVersionTests.cs b/tests/NLog.UnitTests/LayoutRenderers/ApplicationEnvironment/AssemblyVersionTests.cs
@@ -63,12 +63,30 @@ public void EntryAssemblyVersionTest()
            AssertLayoutRendererOutput("${assembly-version}", assemblyVersion);
        }

+        [Fact]
+        public void EntryAssemblyVersionDefaultTest()
+        {
+            var assembly = Assembly.GetEntryAssembly();
+            var assemblyVersion = assembly is null
+                ? "1.2.3.4"
+                : assembly.GetName().Version.ToString();
+            AssertLayoutRendererOutput("${assembly-version:default=1.2.3.4}", assemblyVersion);
+        }
+
        [Fact]
        public void AssemblyNameVersionTest()
        {
            AssertLayoutRendererOutput("${assembly-version:NLogAutoLoadExtension}", "2.0.0.0");
        }

+        [Fact]
+        public void AssemblyNameUnknownVersionTest()
+        {
+            using (new NoThrowNLogExceptions())
+                AssertLayoutRendererOutput("${assembly-version:FooBar:default=1.2.3.4}", "1.2.3.4");
+        }
+
+
        [Fact]
        public void AssemblyNameVersionTypeTest()
        {