Add URL resolving TagHelper to replace Razor ~/ functionality. #2807
Description
This is in reaction to the conversation: aspnet/Razor#427 (comment)
Today Razor special cases ~/ at the beginning of attributes and treats them as "resolve an application relative URL"; however, it does this for every attribute which is overkill/incorrect. After investigating the attributes that have URL capability in Razor the list warrants something less hard coded into the core of Razor to resolve application relative URLs.
The list of HTML5 url based attributes I was able to find are:
- href :
<a>,<area>,<link>,<base> - src :
<audio>,<embed>,<iframe>,<img>,<input>,<script>,<source>,<track>,<video> - action :
<form> - cite :
<blockquote>,<del>,<ins>,<q> - data :
<object> - formaction :
<button>,<input> - icon :
<menuitem> - itemid : everything
- manifest :
<html> - poster :
<video> - archive :
<object>,<applet>
The TagHelper should exist in Microsoft.AspNet.Mvc.Razor and should be auto-added to Razor pages (much like how we auto add @inject directives). It should inspect TagHelperOutput.Attributes and TagHelperOutput.TagName for the various combinations listed above and resolve URLs if they begin with ~/. Lastly, it should have an [EditorBrowsable(EditorBrowsableState.Never)] attribute to prevent excess highlighting in the Razor editor (will work once aspnet/Razor#447 is completed).