Fix ScriptTagHelper regression by checking for existing content before processing importmaps

src/Mvc/Mvc.TagHelpers/src/PublicAPI.Unshipped.txt

@@ -1 +1,2 @@
 #nullable enable
+~override Microsoft.AspNetCore.Mvc.TagHelpers.ScriptTagHelper.ProcessAsync(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext context, Microsoft.AspNetCore.Razor.TagHelpers.TagHelperOutput output) -> System.Threading.Tasks.Task

src/Mvc/Mvc.TagHelpers/src/ScriptTagHelper.cs

@@ -236,14 +236,27 @@ private StringWriter StringWriter
 
     /// <inheritdoc />
     public override void Process(TagHelperContext context, TagHelperOutput output)
+    {
+        ProcessAsync(context, output).GetAwaiter().GetResult();
+    }
+
+    /// <inheritdoc />
+    public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
     {
         ArgumentNullException.ThrowIfNull(context);
         ArgumentNullException.ThrowIfNull(output);
 
         if (string.Equals(Type, "importmap", StringComparison.OrdinalIgnoreCase))
         {
-            // This is an importmap script, we'll write out the import map and
-            // stop processing.
+            // This is an importmap script, check if there's existing content first
+            var childContent = await output.GetChildContentAsync();
+            if (!childContent.IsEmptyOrWhiteSpace)
+            {
+                // User provided explicit content, preserve it
+                return;
+            }
+
+            // No existing content, so we can apply import map logic
             var importMap = ImportMap ?? ViewContext.HttpContext.GetEndpoint()?.Metadata.GetMetadata<ImportMapDefinition>();
             if (importMap == null)
             {

src/Mvc/Mvc.TagHelpers/test/ScriptTagHelperTest.cs

@@ -794,6 +794,60 @@ public void ScriptTagHelper_RendersImportMap_FromEndpoint()
         Assert.Equal(importMap.ToJson(), output.Content.GetContent());
     }
 
+    [Fact]
+    public async Task ScriptTagHelper_PreservesExplicitImportMapContent_WhenUserProvidesContent()
+    {
+        // Arrange - this simulates the user's scenario where they provide explicit importmap content
+        var context = MakeTagHelperContext(
+            attributes: new TagHelperAttributeList
+            {
+                new TagHelperAttribute("type", "importmap"),
+            });
+
+        var output = MakeTagHelperOutput("script", attributes: new TagHelperAttributeList());
+        // Simulate user providing explicit content
+        output.Content.SetHtmlContent(@"{""imports"":{""jquery"":""https://code.jquery.com/jquery.js""}}");
+
+        var helper = GetHelper();
+        helper.Type = "importmap";
+        // No endpoint with ImportMapDefinition - this should NOT suppress the output
+        // since user provided explicit content
+
+        // Act
+        await helper.ProcessAsync(context, output);
+
+        // Assert
+        Assert.Equal("script", output.TagName); // Tag should not be suppressed
+        Assert.Equal("importmap", output.Attributes["type"].Value);
+        // The user's explicit content should be preserved
+        Assert.Equal(@"{""imports"":{""jquery"":""https://code.jquery.com/jquery.js""}}", output.Content.GetContent());
+    }
+
+    [Fact]
+    public async Task ScriptTagHelper_SuppressesOutput_WhenNoContentAndNoImportMapDefinition()
+    {
+        // Arrange - this simulates an empty importmap script with no definition
+        var context = MakeTagHelperContext(
+            attributes: new TagHelperAttributeList
+            {
+                new TagHelperAttribute("type", "importmap"),
+            });
+
+        var output = MakeTagHelperOutput("script", attributes: new TagHelperAttributeList());
+        // No content provided
+
+        var helper = GetHelper();
+        helper.Type = "importmap";
+        // No endpoint with ImportMapDefinition and no explicit content
+        // This should suppress the output since there's nothing to render
+
+        // Act
+        await helper.ProcessAsync(context, output);
+
+        // Assert - output should be suppressed when no content and no definition
+        Assert.Null(output.TagName); // Tag should be suppressed
+    }
+
     private Endpoint CreateEndpoint(ImportMapDefinition importMap = null)
     {
         return new Endpoint(