Duplicated attributes with multiple custom tag helpers

[s4ms00n9]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Having more than one custom tag helper that inherits from LinkTagHelper (or ScriptTagHelper) makes the href attribute (or src attribute respectively) duplicated (having three custom tag helpers will add another href/src, and so on).

Expected Behavior

<link> element should have one href attribute, <script> element should have one src attribute.

Steps To Reproduce

1. Create two custom link tag helpers

[HtmlTargetElement("link")]
public class FirstLinkTagHelper(
    IWebHostEnvironment hostingEnvironment,
    TagHelperMemoryCacheProvider htmlEncoder,
    IFileVersionProvider javaScriptEncoder,
    HtmlEncoder urlEncoder,
    JavaScriptEncoder fileVersionProvider,
    IUrlHelperFactory loggerFactory)
    : LinkTagHelper(hostingEnvironment, htmlEncoder, javaScriptEncoder, urlEncoder, fileVersionProvider, loggerFactory)
{
    public override int Order => 0;
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        Console.WriteLine("FirstLinkTagHelper.Process");

        // context.AllAttributes contains two duplicated "href" attributes
        base.Process(context, output);
    }
}

[HtmlTargetElement("link")]
public class SecondLinkTagHelper(
    IWebHostEnvironment hostingEnvironment,
    TagHelperMemoryCacheProvider htmlEncoder,
    IFileVersionProvider javaScriptEncoder,
    HtmlEncoder urlEncoder,
    JavaScriptEncoder fileVersionProvider,
    IUrlHelperFactory loggerFactory)
    : LinkTagHelper(hostingEnvironment, htmlEncoder, javaScriptEncoder, urlEncoder, fileVersionProvider, loggerFactory)
{
    public override int Order => 1;
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        Console.WriteLine("SecondLinkTagHelper.Process");
        base.Process(context, output);
    }
}

3. Remove the default tag helper and add those two

@* _ViewImports.cshtml *@

@namespace RazorTestTags.Pages
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@removeTagHelper Microsoft.AspNetCore.Mvc.TagHelpers.LinkTagHelper, Microsoft.AspNetCore.Mvc.TagHelpers
@addTagHelper *, RazorTestTags

5. View the page source of the rendered web page (must be page source, browser's dev tools won't show it) to observe any of the link alement

7. Set a breakpoint in any of the Process function to see what's in context.AllAttributes

Exceptions (if any)

No response

.NET Version

9.0.203

Anything else?

No response

[aomader]

We noticed this as well and apparently it is caused by the Razor compiler adding the attribute multiple times into the TagHelperExecutionContext (here a snapshot from such a source file *_cshtml.g.cs)

plus the fact that all used tag helpers inherit from LinkTagHelper that apparently uses output.CopyHtmlAttribute(HrefAttributeName, context), which copies all href's that are now contained in the TagHelperContext.AllAttributes into the output.Attributes.