Implement 'ask for a reset' algorithm for <select> elements

[frewsxcv]

https://html.spec.whatwg.org/multipage/#ask-for-a-reset

[frewsxcv]

Relevant FIXME which was added in #7745

[dagnir]

I'm completely new to servo (and any browser engine dev). From looking at the spec, this seems relatively simple. Is this appropriate for a newcomer?

[jdm]

I believe so! You'll probably want to implement HTMLSelectElement's size attribute, followed by the multiple attribute, (both using appropriate macros from macros.rs) and then add a ask_for_reset method. Let us know if anything is unclear!

[jdm]

Looks like the multiple attribute already is implemented: http://mxr.mozilla.org/servo/source/components/script/dom/htmlselectelement.rs#82

[dagnir]

Thank you. I'll get to work on it

[dagnir]

Hi @jdm, here is what I've put together so far dagnir@c6267df. Please let me know what things need fixing before I send a PR

[jdm]

A few useful changes:

• instead of calling Item in a loop, we should be using traverse_preorder and iterating through the results
• uses of match that only act on the Some branch can be written as if let Some( instead
• uses of if something.is_some() { something.unwrap() } can be written as if let Some( instead
• first_enabled and last_selected can probably be Option<Root<HTMLOptionElement>> instead of indexes
• unfortunately the Disabled method is not quite enough; we need to call get_disabled_state instead

Generally it's easier to make comments like these in our review tool; submitting PRs for early feedback is encouraged :)

[dagnir]

@jdm Thanks! I'lll send PRs in the future