Don't create shadow copy that already exists

DotNetCorePlugins.sln

@@ -124,6 +124,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "WithOurPluginsPluginA", "te
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "WithOurPluginsPluginB", "test\TestProjects\WithOurPluginsPluginB\WithOurPluginsPluginB.csproj", "{D5B3DA06-E60D-4C85-8835-6A26003365AA}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "NativeDependency", "test\TestProjects\NativeDependency\NativeDependency.csproj", "{2837A894-11D6-4DBF-B140-84C97C385A15}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -638,6 +640,18 @@ Global
 		{D5B3DA06-E60D-4C85-8835-6A26003365AA}.Release|x64.Build.0 = Release|Any CPU
 		{D5B3DA06-E60D-4C85-8835-6A26003365AA}.Release|x86.ActiveCfg = Release|Any CPU
 		{D5B3DA06-E60D-4C85-8835-6A26003365AA}.Release|x86.Build.0 = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|x64.Build.0 = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Debug|x86.Build.0 = Debug|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|Any CPU.Build.0 = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|x64.ActiveCfg = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|x64.Build.0 = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|x86.ActiveCfg = Release|Any CPU
+		{2837A894-11D6-4DBF-B140-84C97C385A15}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -691,6 +705,7 @@ Global
 		{7C7B19F2-5822-4DA2-80D2-E077CE705039} = {98E964A2-55DA-4740-9F2E-B64FDF6715DB}
 		{3A7712FC-9A91-4322-AF7E-4FEC6EB0D845} = {98E964A2-55DA-4740-9F2E-B64FDF6715DB}
 		{D5B3DA06-E60D-4C85-8835-6A26003365AA} = {98E964A2-55DA-4740-9F2E-B64FDF6715DB}
+		{2837A894-11D6-4DBF-B140-84C97C385A15} = {98E964A2-55DA-4740-9F2E-B64FDF6715DB}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {B1AF41DC-A03E-47B1-BBDB-3DC27ABD9F74}

src/Plugins/Loader/ManagedLoadContext.cs

@@ -343,7 +343,10 @@ private string CreateShadowCopy(string dllPath)
             var dllFileName = Path.GetFileName(dllPath);
             var shadowCopyPath = Path.Combine(_unmanagedDllShadowCopyDirectoryPath, dllFileName);
 
-            File.Copy(dllPath, shadowCopyPath);
+            if (!File.Exists(shadowCopyPath))
+            {
+                File.Copy(dllPath, shadowCopyPath);
+            }
 
             return shadowCopyPath;
         }

test/Plugins.Tests/McMaster.NETCore.Plugins.Tests.csproj

@@ -29,6 +29,7 @@
     <TestProject Include="..\TestProjects\XunitSample\XunitSample.csproj" />
     <TestProject Include="..\TestProjects\SqlClientApp\SqlClientApp.csproj" />
     <TestProject Include="..\TestProjects\TransitivePlugin\TransitivePlugin.csproj" />
+    <TestProject Include="..\TestProjects\NativeDependency\NativeDependency.csproj" Condition=" '$(TargetFramework)' == 'netcoreapp3.1' " />
     <PublishedTestProject Include="..\TestProjects\PowerShellPlugin\PowerShellPlugin.csproj" />
     <MultitargetTestProject Include="..\TestProjects\WithOwnPlugins\WithOwnPlugins.csproj" />
   </ItemGroup>

test/Plugins.Tests/ShadowCopyTests.cs

@@ -0,0 +1,28 @@
+#if NETCOREAPP3_1
+
+using Xunit;
+
+namespace McMaster.NETCore.Plugins.Tests
+{
+    public class ShadowCopyTests
+    {
+        [Fact]
+        public void DoesNotThrowWhenLoadingSameNativeDependecyMoreThanOnce()
+        {
+            var samplePath = TestResources.GetTestProjectAssembly("NativeDependency");
+
+            using var loader = PluginLoader
+                .CreateFromAssemblyFile(samplePath, config => config.EnableHotReload = true);
+
+            var nativeDependecyLoadMethod = loader.LoadDefaultAssembly()
+                .GetType("NativeDependency.NativeDependencyLoader")
+                .GetMethod("Load");
+
+            var exception = Record.Exception(() => nativeDependecyLoadMethod.Invoke(null, null));
+
+            Assert.Null(exception);
+        }
+    }
+}
+
+#endif

test/TestProjects/NativeDependency/NativeDependency.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="System.Data.SQLite" Version="1.0.113.1" />
+  </ItemGroup>
+
+</Project>

test/TestProjects/NativeDependency/NativeDependencyLoader.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using System.Data.SQLite;
+
+namespace NativeDependency
+{
+    public static class NativeDependencyLoader
+    {
+        public static void Load()
+        {
+            using var tempFile = new TempFile("db.sqlite");
+            using var dbConnection = new SQLiteConnection($"Data Source={tempFile.FilePath}");
+
+            dbConnection.Open();
+        }
+    }
+
+    public class TempFile : IDisposable
+    {
+        public TempFile(string fileName)
+        {
+            FilePath = Path.Combine(Path.GetTempPath(), fileName);
+        }
+
+        public string FilePath { get; }
+
+        public void Dispose()
+        {
+            if (!File.Exists(FilePath))
+            {
+                return;
+            }
+
+            File.Delete(FilePath);
+        }
+    }
+}