Add an example for LoggerMessageAttribute (#2792)

docs/Directory.Build.props

@@ -4,7 +4,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <!-- https://dotnet.microsoft.com/download/dotnet-core -->
-    <TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>
+    <TargetFrameworks>netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
     <!-- https://dotnet.microsoft.com/download/dotnet-framework -->
     <TargetFrameworks Condition="$(OS) == 'Windows_NT'">$(TargetFrameworks);net461;net462;net47;net471;net472;net48</TargetFrameworks>
   </PropertyGroup>
@@ -14,6 +14,6 @@
       Please sort alphabetically.
       Refer to https://docs.microsoft.com/nuget/concepts/package-versioning for semver syntax.
     -->
-    <MicrosoftExtensionsLoggingPkgVer>[5.0.0,6.0)</MicrosoftExtensionsLoggingPkgVer>
+    <MicrosoftExtensionsLoggingPkgVer>[6.0.0,)</MicrosoftExtensionsLoggingPkgVer>
   </PropertyGroup>
 </Project>

docs/logs/source-generation/FoodSupplyLogs.cs

@@ -0,0 +1,38 @@
+// <copyright file="FoodSupplyLogs.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using Microsoft.Extensions.Logging;
+
+public static partial class FoodSupplyLogs
+{
+    [LoggerMessage(
+        EventId = 1,
+        Level = LogLevel.Information,
+        Message = "Food `{name}` price changed to `{price}`.")]
+    public static partial void FoodPriceChanged(this ILogger logger, string name, double price);
+
+    [LoggerMessage(
+        EventId = 2,
+        Message = "A `{productType}` recall notice was published for `{brandName} {productDescription}` produced by `{companyName}` ({recallReasonDescription}).")]
+    public static partial void FoodRecallNotice(
+        this ILogger logger,
+        LogLevel logLevel,
+        string brandName,
+        string productDescription,
+        string productType,
+        string recallReasonDescription,
+        string companyName);
+}

docs/logs/source-generation/Program.cs

@@ -0,0 +1,47 @@
+// <copyright file="Program.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using Microsoft.Extensions.Logging;
+using OpenTelemetry.Logs;
+
+public class Program
+{
+    public static void Main()
+    {
+        using var loggerFactory = LoggerFactory.Create(builder =>
+        {
+            builder.AddOpenTelemetry(options =>
+            {
+                options.IncludeScopes = true;
+                options.ParseStateValues = true;
+                options.IncludeFormattedMessage = true;
+                options.AddConsoleExporter();
+            });
+        });
+
+        var logger = loggerFactory.CreateLogger<Program>();
+
+        logger.FoodPriceChanged("artichoke", 9.99);
+
+        logger.FoodRecallNotice(
+            logLevel: LogLevel.Critical,
+            brandName: "Contoso",
+            productDescription: "Salads",
+            productType: "Food & Beverages",
+            recallReasonDescription: "due to a possible health risk from Listeria monocytogenes",
+            companyName: "Contoso Fresh Vegetables, Inc.");
+    }
+}

docs/logs/source-generation/README.md

@@ -0,0 +1,8 @@
+# Compile-time logging source generation
+
+.NET 6 has introduced a more usable and performant logging solution with
+[`LoggerMessageAttribute`](https://docs.microsoft.com/dotnet/api/microsoft.extensions.logging.loggermessageattribute).
+
+## References
+
+* [Compile-time logging source generation](https://docs.microsoft.com/dotnet/core/extensions/logger-message-generator)

docs/logs/source-generation/source-generation.csproj

@@ -0,0 +1,6 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="$(MicrosoftExtensionsLoggingPkgVer)" />
+    <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Console\OpenTelemetry.Exporter.Console.csproj" />
+  </ItemGroup>
+</Project>