Load rustdoc's JS search index on-demand.

Instead of being loaded on every page, the JS search index is now
loaded when either (a) there is a `?search=` param, or (b) the search
input is focused.

This saves both CPU and bandwidth. As of Feb 2021,
https://doc.rust-lang.org/search-index1.50.0.js is 273,838 bytes
gzipped or 2,544,939 bytes uncompressed. Evaluating it takes 445 ms
of CPU time in Chrome 88 on a i7-10710U CPU (out of a total ~2,100
ms page reload).

Generate separate JS file with crate names.

This is much smaller than the full search index, and is used in the "hot
path" to draw the page. In particular it's used to crate the dropdown
for the search bar, and to append a list of crates to the sidebar (on
some pages).

Skip early search that can bypass 500ms timeout.

This was occurring when someone had typed some text during the load of
search-index.js. Their query was usually not ready to execute, and the
search itself is fairly expensive, delaying the overall load, which
delayed the input / keyup events, which delayed eventually executing the
query.

1 files changed, 10 insertions, 7 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 58e9e41e6a5..dd531f15102 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1039,10 +1039,12 @@ themePicker.onblur = handleThemeButtonsBlur;
         cx.shared.fs.write(&dst, v.as_bytes())?;
     }
 
-    // Update the search index
+    // Update the search index and crate list.
     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.as_str()), &dst);
     all_indexes.push(search_index);
+    krates.push(krate.name.to_string());
+    krates.sort();
 
     // Sort the indexes by crate so the file will be generated identically even
     // with rustdoc running in parallel.
@@ -1050,11 +1052,15 @@ themePicker.onblur = handleThemeButtonsBlur;
     {
         let mut v = String::from("var searchIndex = JSON.parse('{\\\n");
         v.push_str(&all_indexes.join(",\\\n"));
-        // "addSearchOptions" has to be called first so the crate filtering can be set before the
-        // search might start (if it's set into the URL for example).
-        v.push_str("\\\n}');\naddSearchOptions(searchIndex);initSearch(searchIndex);");
+        v.push_str("\\\n}');\ninitSearch(searchIndex);");
         cx.shared.fs.write(&dst, &v)?;
     }
+
+    let crate_list_dst = cx.dst.join(&format!("crates{}.js", cx.shared.resource_suffix));
+    let crate_list =
+        format!("window.ALL_CRATES = [{}];", krates.iter().map(|k| format!("\"{}\"", k)).join(","));
+    cx.shared.fs.write(&crate_list_dst, &crate_list)?;
+
     if options.enable_index_page {
         if let Some(index_page) = options.index_page.clone() {
             let mut md_opts = options.clone();
@@ -1076,9 +1082,6 @@ themePicker.onblur = handleThemeButtonsBlur;
                 extra_scripts: &[],
                 static_extra_scripts: &[],
             };
-            krates.push(krate.name.to_string());
-            krates.sort();
-            krates.dedup();
 
             let content = format!(
                 "<h1 class=\"fqn\">\