rustdoc: Merge "Structs", "Enums", "Unions", and "Type Definitions" sections on module pages

[camelid]

Summary

Merge the following sections that appear on module (and crate) pages into a single "Types" section:

• Structs
• Enums
• Unions
• Type Definitions

Why?

• Usually, the exact kind of type something is doesn't matter when you're looking at an overview.
• It can be confusing to have to so many sections, and it creates more places where you have to look for what you want.
• After the recent color reduction PR (rustdoc: use smaller number of colors to distinguish items #91480), the types are no longer colored differently, so it makes more sense to merge their sections.

[camelid]

cc @jsha

[jsha]

Terrific idea!

[GuillaumeGomez]

I'm not completely sold on the idea. Something about it is bothering me but I can't put the finger on it... Well, for now let's say I'm neutral.

[wackbyte]

I find the current layout simpler than what's being proposed here. I can understand the reasoning behind it, but each kind of type is fundamentally different in a way where it's quite useful to see them laid out separately.

[redgoldlace]

I understand that the intent here is to simplify the sidebar and make things seem less verbose, but (particularly relating to type definitions) I'm not really a fan of the change. It can be very helpful to know when something falls into a specific "class" of type - without having to jump to its position in the documentation or inspect the source - and I would really hate to lose that. I wouldn't be opposed to making it some sort of a configurable option, but I do think such a proposal does more harm to documentation than good.

I suppose one alternative would be to merge them into a Types section, but add a prefix to each name in the sidebar such as struct, enum, union and etc. That way you can have your cake and eat it too - there isn't a loss of information, but things do get unified nicely. One issue with that idea is the amount of horizontal space taken up by the sidebar, but I'm not sure how much of an impact that would have.

[ThePuzzlemaker]

I support what @kaylynn234 suggests.

I feel like doing this would be counterproductive. I've found that I've had many cases where I need to looking over a module and need to find a specific enum or struct but don't remember the name. And I can't necessarily search for it with enum: if I don't know the name, as doing something like just enum: doesn't work.

Take, for example, an AST module. If designed in a certain way, e.g. Rust's AST/HIR, it will have main structures Foo as well as FooKind enum. Often the module is already quite cluttered, and the structures usually don't contain all the information that you need, instead the enums. If the sections were combined it would become even harder to find a specific enum that you need, so either you have to search through a mess of types to find a struct and then navigate to the enum, or try to guess the name that you need.

For most people, this change will probably not have much effect. But for me, it honestly would likely decrease my ability to navigate certain docs, especially in my programming language projects.

I've already found that removing the color difference between structs and enums and etc. (from #91480) has impacted my ability to navigate through documentation. While I'll likely get used to this, combining the sections would amplify this problem.

[camelid]

Hmm, okay. I won't make this change then. What about just moving the sections so they're all next to each other? Currently, the type alias section is at the bottom, while the others are at the top. Instead, I think they should all be at the top.