feat: support Go comments within HTML tag attributes

[jackielii]

Summary

Implements support for single-line (//) and multi-line (/* */) Go comments within HTML element attributes, addressing issue #866.

Problem

Previously, templ did not allow Go comments within HTML tag attributes, requiring developers to place comments above the element which wasn't always convenient for documenting specific attributes.

Solution

This PR adds support for Go-style comments directly within HTML tag attributes. The comments are parsed and stored in the AST but excluded from the generated output.

Example

<form
  class="flex"
  // This comment explains why the following attribute is necessary
  action="javascript:void(0)"
  /* Multi-line comment
     for more detailed explanations */
  method="post"
>

Changes

• Added AttributeComment type to represent comments within attributes
• Updated parser to recognize and handle comments between attributes
• Updated generator to skip comments during code generation
• Added comprehensive test coverage in generator/test-attribute-comments/

Testing

• Added test case following the existing test pattern in the generator folder
• Test verifies that comments are properly excluded from generated output
• All existing tests continue to pass

Fixes #866

[jackielii]

@a-h @joerdav anything else you need for this PR?

[joerdav]

Besides the 1 comment I think this looks good, @a-h any thoughts?

[joerdav]

Maybe could do with some tests with attribute values that contain // just to ensure no odd edge cases!

[jackielii]

Maybe could do with some tests with attribute values that contain // just to ensure no odd edge cases!

added edge case tests in https://github.com/jackielii/templ/blob/feat/attribute-comments/generator/test-attribute-comments/template.templ#L41-L68

[jackielii]

@a-h anything else you need?

[b0ch3nski]

This is a really cool feature! Do we need anything else here?

[a-h]

@joerdav - we discussed this one last Friday, right?

IIRC, we said we'd merge it.

I was a bit reluctant because it's hard to walk something back once you've added it, and it changes the syntax highlighting and some other stuff.

[jackielii]

I've been using this patch over a year now. I'm exclusive Neovim user, the treesitter already supports this. I think it's a natural extension to existing syntax: support commenting inside the HTML tag is less unexpected than not supporting it.

[a-h]

Agreed. I'm merging this today, just fixing the conflicts.