Do not override existing web.config during IIS publish

src/Components/WebAssembly/Build/src/targets/Publish.targets

@@ -15,25 +15,31 @@
     Condition="'$(BlazorPrunePublishOutput)' != 'false'">
 
     <ItemGroup>
-      <!-- Delete stray contents from the root of the the app. -->
+      <!-- Delete stray DLLs from the application. -->
       <ResolvedFileToPublish
         Remove="%(ResolvedFileToPublish.Identity)"
-        Condition="!$([System.String]::Copy('%(ResolvedFileToPublish.RelativePath)').Replace('\','/').StartsWith('wwwroot/'))"/>
+        Condition="$([System.String]::Copy('%(ResolvedFileToPublish.RelativePath)').EndsWith('dll'))"/>
+      <!--Remove stray debugging files.-->
+      <ResolvedFileToPublish
+        Remove="%(ResolvedFileToPublish.Identity)"
+        Condition="$([System.String]::Copy('%(ResolvedFileToPublish.RelativePath)').EndsWith('pdb'))"/>
+      <!--Remove excluded static assets.-->
+      <ResolvedFileToPublish
+        Remove="%(ResolvedFileToPublish.Identity)"
+        Condition="$([System.String]::Copy('%(ResolvedFileToPublish.RelativePath)').Replace('\','/').StartsWith('Excluded-Static-Web-Assets/'))"/>
     </ItemGroup>
   </Target>
 
+  <!--After moving the resolved files to the publish directory, we can determine
+  whether or not to copy the standalone config if the user has not provided
+  their own.-->
   <Target
       Name="_BlazorCopyStandaloneWebConfig"
-      AfterTargets="_BlazorCleanupPublishOutput;ComputeResolvedFilesToPublishList">
+      AfterTargets="CopyFilesToPublishDirectory"
-
+      Condition="!Exists('$(PublishDir)web.config')">
-    <ItemGroup>
+    <WriteLinesToFile
-      <ResolvedFileToPublish Include="$(MSBuildThisFileDirectory)Standalone.Web.config">
+      File="$(PublishDir)web.config"
-        <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
+      Lines="$([System.IO.File]::ReadAllText('$(MSBuildThisFileDirectory)Standalone.Web.config'))" />
-        <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
-        <RelativePath>web.config</RelativePath>
-      </ResolvedFileToPublish>
-    </ItemGroup>
-
   </Target>
 
 </Project>

src/Components/WebAssembly/Build/test/BuildIntegrationTests/PublishIntegrationTest.cs

@@ -101,6 +101,29 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
             Assert.FileCountEquals(result, 1, publishDirectory, "*", SearchOption.TopDirectoryOnly);
         }
 
+        [Fact]
+        public async Task Publish_WithExistingWebConfig_Works()
+        {
+            // Arrange
+            using var project = ProjectDirectory.Create("standalone", additionalProjects: new[] { "razorclasslibrary", "LinkBaseToWebRoot" });
+            project.Configuration = "Release";
+
+            var webConfigContents = "test webconfig contents";
+            AddFileToProject(project, "web.config", webConfigContents);
+
+            var result = await MSBuildProcessManager.DotnetMSBuild(project, "Publish");
+
+            Assert.BuildPassed(result);
+
+            var publishDirectory = project.PublishOutputDirectory;
+
+            var blazorPublishDirectory = Path.Combine(publishDirectory, "wwwroot");
+
+            // Verify web.config
+            Assert.FileExists(result, publishDirectory, "web.config");
+            Assert.FileContains(result, Path.Combine(publishDirectory, "web.config"), webConfigContents);
+        }
+
         [Fact]
         public async Task Publish_WithNoBuild_Works()
         {
@@ -392,6 +415,13 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Build
             File.WriteAllText(path, updated);
         }
 
+        private static void AddFileToProject(ProjectDirectory project, string filename, string content)
+        {
+            var path = Path.Combine(project.DirectoryPath, filename);
+            File.WriteAllText(path, content);
+        }
+
+
         private static void VerifyBootManifestHashes(MSBuildResult result, string blazorPublishDirectory)
         {
             var bootManifestResolvedPath = Assert.FileExists(result, blazorPublishDirectory, "_framework", "blazor.boot.json");