fix(rustdoc): generics search

This commit adds a test case for generics, re-adds generics data
to the search index, and tweaks function indexing to use less space in JSON.

This reverts commit 14ca89446c.

src/librustdoc/html/render/cache.rs

@@ -219,6 +219,7 @@ crate fn get_index_search_type<'tcx>(
 fn get_index_type(clean_type: &clean::Type) -> RenderType {
     RenderType {
         name: get_index_type_name(clean_type, true).map(|s| s.as_str().to_ascii_lowercase()),
+        generics: get_generics(clean_type),
     }
 }
 
@@ -251,6 +252,23 @@ fn get_index_type_name(clean_type: &clean::Type, accept_generic: bool) -> Option
     }
 }
 
+/// Return a list of generic parameters for use in the search index.
+///
+/// This function replaces bounds with types, so that `T where T: Debug` just becomes `Debug`.
+/// It does return duplicates, and that's intentional, since search queries like `Result<usize, usize>`
+/// are supposed to match only results where both parameters are `usize`.
+fn get_generics(clean_type: &clean::Type) -> Option<Vec<String>> {
+    clean_type.generics().and_then(|types| {
+        let r = types
+            .iter()
+            .filter_map(|t| {
+                get_index_type_name(t, false).map(|name| name.as_str().to_ascii_lowercase())
+            })
+            .collect::<Vec<_>>();
+        if r.is_empty() { None } else { Some(r) }
+    })
+}
+
 /// The point of this function is to replace bounds with types.
 ///
 /// i.e. `[T, U]` when you have the following bounds: `T: Display, U: Option<T>` will return

src/librustdoc/html/render/mod.rs

@@ -96,6 +96,7 @@ crate struct IndexItem {
 #[derive(Debug)]
 crate struct RenderType {
     name: Option<String>,
+    generics: Option<Vec<String>>,
 }
 
 /// Full type of functions/methods in the search index.
@@ -149,7 +150,13 @@ impl Serialize for TypeWithKind {
     where
         S: Serializer,
     {
-        (&self.ty.name, self.kind).serialize(serializer)
+        let mut seq = serializer.serialize_seq(None)?;
+        seq.serialize_element(&self.ty.name)?;
+        seq.serialize_element(&self.kind)?;
+        if let Some(generics) = &self.ty.generics {
+            seq.serialize_element(generics)?;
+        }
+        seq.end()
     }
 }