This is a type for efficiently and easily constructing the part of a URL
after the domain: `nightly/core/str/struct.Bytes.html`.
It allows simplifying some code and avoiding some allocations in the
`href_*` functions.
It will also allow making `Cache.paths` et al. use `Symbol` without
having to allocate `String`s in the `href_*` functions. `String`s would
be necessary otherwise because `Symbol::as_str()` returns `SymbolStr`,
whose `Deref<Target = str>` impl requires the `str` to not outlive it.
This is the primary motivation for the addition of `UrlPartsBuilder`.
This commit refactors the implementation of
`markdown_summary_with_limit()`, separating the logic of determining
when the limit has been reached from the actual rendering process.
The main advantage of the new approach is that it guarantees that all
HTML tags are closed, whereas the previous implementation could generate
tags that were never closed. It also ensures that no empty tags are
generated (e.g., `<em></em>`).
The new implementation consists of a general-purpose struct
`HtmlWithLimit` that manages the length-limiting logic and a function
`markdown_summary_with_limit()` that renders Markdown to HTML using the
struct.
Instead of using a depth counter and adding "../" to get to the top,
this commit makes rustdoc actually compare the path of what it's
linking from to the path that it's linking to. This makes the resulting
HTML shorter.
Here's a comparison of one of the largest (non-source) files in the
Rust standard library docs (about 4% improvement before gzipping).
$ wc -c struct.Wrapping.old.html struct.Wrapping.new.html
2387389 struct.Wrapping.old.html
2298538 struct.Wrapping.new.html
Most if it can be efficiently gzipped away.
$ wc -c struct.Wrapping.old.html.gz struct.Wrapping.new.html.gz
70679 struct.Wrapping.old.html.gz
70050 struct.Wrapping.new.html.gz
But it also makes a difference in the final DOM size, reducing it from 91MiB to 82MiB.
Almost all of the modules are crate-private, except for
`rustdoc::json::types`, which I believe is intended to be for public
use; and `rustdoc::html::markdown`, which is used externally by the
error-index generator and so has to be public.
