Go to Definition on tag helper doesn't work for wildcard attributes

[davidwengier]

Then there is a bug if the tag already has other tag helpers.

This works:

<label for="test" foo="1">test</label>

This does not:

<label asp-for="test" foo="1">test</label>

Sample tag helper:

[HtmlTargetElement("*", Attributes = FooAttributeName)]
public class FooTaghelper: TagHelper
{
    private const string FooAttributeName = "foo";

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.Attributes.Add("foo", "bar");
    }
}

Originally posted by @ChrisVanDijk in #12208

[ChrisVanDijk]

It does work if FooTaghelper is the only tag helper on that tag, also for wildcard attributes. It does not work if there is a asp tag helper.

It also works if you add multiple custom tag helpers (without using the asp helpers), but then it can jump to the wrong tag helper, I will create a new issue for that.

[davidwengier]

Oh, its probably not the wildcard then, its probably the tag helper for the label tag confusing it. Or the combination of both. Either way, clearly we need some more exhaustive tests, so any scenarios you find are much appreciated!

[davidwengier]

Oh yeah, debugged into it, the code is still just designed for components, so its assuming all attributes belong to the same "tag helper" as the tag itself. If its easier, feel free to just add more comments here with other scenarios, I'll try to get them all at once as they're probably similar fixes, if not the same.

[ChrisVanDijk]

I just created #12211 for the issue with 2 or more custom tag helpers. If you want I can close it and put the example in this issue.

[davidwengier]

No, that's fine. In fact, I probably shouldn't have said anything. More issues is always good, its easy to close two issues with one PR, but hard to know what to do when one PR only fixes half an issue :)

[ChrisVanDijk]

The problem with the example from this issue is caused by the asp helper. If you remove it, it works. So it looks like it doesn't like tag helpers that are in an external assembly.

To test that idea:

• I created a Razor Class Library called DemoTagHelpers with a simple tag helper:

namespace DemoTagHelpers;

[HtmlTargetElement("label", Attributes = BarAttributeName)]
public class ExternalTestTaghelper : TagHelper
{
    private const string BarAttributeName = "externaltest";

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.Attributes.Add("externaltest", "I like VS 2026 so far");
    }
}

• In my MVC demo project: added a assembly reference to the dll we just build (so not the project)
• Imported the reference in _ViewImports.cshtml (@addTagHelper *, DemoTagHelpers)
• Added a label with the attribute to a view:

<label for="test" externaltest="external">test</label>

• Verified that when you hover with your mouse cursor mouse the popup shows "DemoTagHelpers.ExternalTestTaghelper"
• Pressed F12 when on the attribute
• Nothing happens

Then we add another tag helper, a internal one, the foo helper to the tag:

<label for="test" externaltest="external" foo="1">test</label>

And I think because of #12211 it doesn't jump to the foo helper.

If I remove the externaltest attribute so we end up with <label for="test" foo="1">test</label>, it jumps correctly to the foo helper.