Add custom export attribute that only exports for a named process

This lets us define exports that are available inside Visual Studio but not Blend.

Author: jcansdale

src/GitHub.Exports/Exports/ExportForProcess.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Diagnostics;
+using System.ComponentModel.Composition;
+
+namespace GitHub.Exports
+{
+    /// <summary>
+    /// Only expose export when executing in specific named process.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = true)]
+    public sealed class ExportForProcessAttribute : ExportAttribute
+    {
+        /// <summary>
+        /// Define an export that is only exposed in a specific named process.
+        /// </summary>
+        /// <param name="contractType">The contract type to expose.</param>
+        /// <param name="processName">Name of the process to expose export from (e.g. 'devenv').</param>
+        public ExportForProcessAttribute(Type contractType, string processName) : base(ExportForProcess(contractType, processName))
+        {
+            ProcessName = processName;
+        }
+
+        static Type ExportForProcess(Type contractType, string processName)
+        {
+            return Process.GetCurrentProcess().ProcessName == processName ? contractType : null;
+        }
+
+        /// <summary>
+        /// The process name export will be exposed in.
+        /// </summary>
+        public string ProcessName { get; }
+    }
+}

src/GitHub.Exports/GitHub.Exports.csproj

@@ -129,6 +129,7 @@
     <Reference Include="WindowsBase" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Exports\ExportForProcess.cs" />
     <Compile Include="GlobalCommands.cs" />
     <Compile Include="Models\DiffChangeType.cs" />
     <Compile Include="Models\DiffChunk.cs" />