rustdoc-search: shard the search result descriptions

The descriptions are, on almost all crates[^1], the majority
of the size of the search index, even though they aren't really
used for searching. This makes it relatively easy to separate
them into their own files.

This commit also bumps us to ES8. Out of the browsers we support,
all of them support async functions according to caniuse.

https://caniuse.com/async-functions

[^1]:
    <https://microsoft.github.io/windows-docs-rs/>, a crate with
    44MiB of pure names and no descriptions for them, is an outlier
    and should not be counted.

1 files changed, 29 insertions, 2 deletions

diff --git a/src/librustdoc/html/render/write_shared.rs b/src/librustdoc/html/render/write_shared.rs
index fbd45b2b48e..c806bf1cc66 100644
--- a/src/librustdoc/html/render/write_shared.rs
+++ b/src/librustdoc/html/render/write_shared.rs
@@ -24,6 +24,7 @@ use crate::formats::cache::Cache;
 use crate::formats::item_type::ItemType;
 use crate::formats::Impl;
 use crate::html::format::Buffer;
+use crate::html::render::search_index::SerializedSearchIndex;
 use crate::html::render::{AssocItemLink, ImplRenderingParameters};
 use crate::html::{layout, static_files};
 use crate::visit::DocVisitor;
@@ -46,7 +47,7 @@ use crate::{try_err, try_none};
 pub(super) fn write_shared(
     cx: &mut Context<'_>,
     krate: &Crate,
-    search_index: String,
+    search_index: SerializedSearchIndex,
     options: &RenderOptions,
 ) -> Result<(), Error> {
     // Write out the shared files. Note that these are shared among all rustdoc
@@ -312,7 +313,7 @@ pub(super) fn write_shared(
     let dst = cx.dst.join(&format!("search-index{}.js", cx.shared.resource_suffix));
     let (mut all_indexes, mut krates) =
         try_err!(collect_json(&dst, krate.name(cx.tcx()).as_str()), &dst);
-    all_indexes.push(search_index);
+    all_indexes.push(search_index.index);
     krates.push(krate.name(cx.tcx()).to_string());
     krates.sort();
 
@@ -335,6 +336,32 @@ else if (window.initSearch) window.initSearch(searchIndex);
         Ok(v.into_bytes())
     })?;
 
+    let search_desc_dir = cx.dst.join(format!("search.desc/{krate}", krate = krate.name(cx.tcx())));
+    if Path::new(&search_desc_dir).exists() {
+        try_err!(std::fs::remove_dir_all(&search_desc_dir), &search_desc_dir);
+    }
+    try_err!(std::fs::create_dir_all(&search_desc_dir), &search_desc_dir);
+    let kratename = krate.name(cx.tcx()).to_string();
+    for (i, (_, data)) in search_index.desc.into_iter().enumerate() {
+        let output_filename = static_files::suffix_path(
+            &format!("{kratename}-desc-{i}-.js"),
+            &cx.shared.resource_suffix,
+        );
+        let path = search_desc_dir.join(output_filename);
+        try_err!(
+            std::fs::write(
+                &path,
+                &format!(
+                    r##"searchState.loadedDescShard({kratename}, {i}, {data})"##,
+                    kratename = serde_json::to_string(&kratename).unwrap(),
+                    data = serde_json::to_string(&data).unwrap(),
+                )
+                .into_bytes()
+            ),
+            &path
+        );
+    }
+
     write_invocation_specific("crates.js", &|| {
         let krates = krates.iter().map(|k| format!("\"{k}\"")).join(",");
         Ok(format!("window.ALL_CRATES = [{krates}];").into_bytes())