Rollup merge of #83237 - notriddle:short-links, r=jyn514

rustdoc: use more precise relative URLs

This is a fairly large diff, and will probably conflict with #82815 since it reduces (but does not eliminate) the use of the old depth variable.

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.

src/librustdoc/clean/types.rs

@@ -41,6 +41,7 @@ use crate::core::DocContext;
 use crate::formats::cache::Cache;
 use crate::formats::item_type::ItemType;
 use crate::html::render::cache::ExternalLocation;
+use crate::html::render::Context;
 
 use self::FnRetTy::*;
 use self::ItemKind::*;
@@ -193,19 +194,18 @@ impl Item {
         self.attrs.collapsed_doc_value()
     }
 
-    crate fn links(&self, cache: &Cache) -> Vec<RenderedLink> {
+    crate fn links(&self, cx: &Context<'_>) -> Vec<RenderedLink> {
         use crate::html::format::href;
-        use crate::html::render::CURRENT_DEPTH;
 
-        cache
+        cx.cache()
             .intra_doc_links
             .get(&self.def_id)
             .map_or(&[][..], |v| v.as_slice())
             .iter()
-            .filter_map(|ItemLink { link: s, link_text, did, fragment }| {
+            .filter_map(|ItemLink { link: s, link_text, did, ref fragment }| {
                 match *did {
                     Some(did) => {
-                        if let Some((mut href, ..)) = href(did, cache) {
+                        if let Some((mut href, ..)) = href(did, cx) {
                             if let Some(ref fragment) = *fragment {
                                 href.push('#');
                                 href.push_str(fragment);
@@ -219,16 +219,26 @@ impl Item {
                             None
                         }
                     }
+                    // FIXME(83083): using fragments as a side-channel for
+                    // primitive names is very unfortunate
                     None => {
+                        let relative_to = &cx.current;
                         if let Some(ref fragment) = *fragment {
-                            let url = match cache.extern_locations.get(&self.def_id.krate) {
+                            let url = match cx.cache().extern_locations.get(&self.def_id.krate) {
                                 Some(&(_, _, ExternalLocation::Local)) => {
-                                    let depth = CURRENT_DEPTH.with(|l| l.get());
-                                    "../".repeat(depth)
+                                    if relative_to[0] == "std" {
+                                        let depth = relative_to.len() - 1;
+                                        "../".repeat(depth)
+                                    } else {
+                                        let depth = relative_to.len();
+                                        format!("{}std/", "../".repeat(depth))
+                                    }
+                                }
+                                Some(&(_, _, ExternalLocation::Remote(ref s))) => {
+                                    format!("{}/std/", s.trim_end_matches('/'))
                                 }
-                                Some(&(_, _, ExternalLocation::Remote(ref s))) => s.to_string(),
                                 Some(&(_, _, ExternalLocation::Unknown)) | None => format!(
-                                    "https://doc.rust-lang.org/{}",
+                                    "https://doc.rust-lang.org/{}/std/",
                                     crate::doc_rust_lang_org_channel(),
                                 ),
                             };
@@ -238,9 +248,8 @@ impl Item {
                                 original_text: s.clone(),
                                 new_text: link_text.clone(),
                                 href: format!(
-                                    "{}{}std/primitive.{}.html{}",
+                                    "{}primitive.{}.html{}",
                                     url,
-                                    if !url.ends_with('/') { "/" } else { "" },
                                     &fragment[..tail],
                                     &fragment[tail..]
                                 ),