[rustdoc] Sort items alphabetically in the sidebar

[GuillaumeGomez]

Currently, the items on the rustdoc pages are sorted in the order of apparition in the source code. I think it'd be nicer to have them sorted alphabetically.

cc @rust-lang/docs @rust-lang/rustdoc @Geal

[the8472]

Items that are related may be grouped in the source, sorting would remove that association. E.g. you can find Vec::new and Vec::with_capacity next to each other and on top since those are likely the first method you'll need.

[QuietMisdreavus]

Items on module pages are already sorted - the --sort-modules-by-appearance flag disables this behavior.

If we start sorting things on other pages - methods, fields, variants, etc - it needs to be more intelligent than "alphabetically". For example, there have been requests in the past for sorting "static methods" (that don't take self) above others. In this case we'd also have to account for the fact that associated methods are also groups up by impl block, and we treat separate impl blocks independently. If we're going to sort things between blocks, or group them in a different manner, we need to approach that first.

[QuietMisdreavus]

One thing i would like to see is grouping things that aren't methods (e.g. associated consts, i don't know if there's anything else you can associate to a type right now) separately from methods. We already break out associated types for traits, it seems right to break out associated consts from the "Methods" section.

[nagisa]

Re-sorting alphabetically something that is often carefully sorted by the author already (in source) seems… wrong. At the very least there is a good reason why constructing methods appear first in the source, then many of the deconstructing methods, then first and last, first_mut and last_mut etc close together, etc.

Adding extra heuristics will help with some of the groupings and orderings but not the others.

[GuillaumeGomez]

That's a lot of things I didn't think about. Also, if there is already a flag to disable it, then it's all fine.

[Geal]

@GuillaumeGomez @QuietMisdreavus sorry I couldn't participate on this last night, but I have something to add: keeping the declaration order is nice, but what I would really like is that the index on the left of the page be sorted.
Keeping methods close to each other when they're related in the main content is useful. But an unsorted index is a bit awkward to use.

[GuillaumeGomez]

@Geal On this point I agree. I reopen the issue with this purpose.

[nox]

It would be nice to at least order trait implementations alphabetically, the current order doesn't even seem to relate in any way with the order of the things in source code.