rustdoc: Shrink ItemInner a bit more

It's now even smaller than before I added the `doc_value_cache` to
`Attributes`. That's because in addition to boxing the cache field, I
also converted `doc_strings` to be a `ThinVec` like the `other_attrs`
field already is.

Author: camelid

compiler/rustc_resolve/src/rustdoc.rs

@@ -200,10 +200,10 @@ pub fn add_doc_fragment(out: &mut String, frag: &DocFragment) {
 pub fn attrs_to_doc_fragments<'a, A: AttributeExt + Clone + 'a>(
     attrs: impl Iterator<Item = (&'a A, Option<DefId>)>,
     doc_only: bool,
-) -> (Vec<DocFragment>, ThinVec<A>) {
+) -> (ThinVec<DocFragment>, ThinVec<A>) {
     let (min_size, max_size) = attrs.size_hint();
     let size_hint = max_size.unwrap_or(min_size);
-    let mut doc_fragments = Vec::with_capacity(size_hint);
+    let mut doc_fragments = ThinVec::with_capacity(size_hint);
     let mut other_attrs = ThinVec::<A>::with_capacity(if doc_only { 0 } else { size_hint });
     for (attr, item_id) in attrs {
         if let Some((doc_str, fragment_kind)) = attr.doc_str_and_fragment_kind() {

src/librustdoc/clean/types.rs

@@ -1005,14 +1005,14 @@ pub struct RenderedLink {
 #[derive(Clone, Debug, Default)]
 pub(crate) struct Attributes {
     /// IMPORTANT! This should not be mutated since then `doc_value_cache` will be invalid.
-    doc_strings: Vec<DocFragment>,
+    doc_strings: ThinVec<DocFragment>,
     pub(crate) other_attrs: ThinVec<hir::Attribute>,
-    doc_value_cache: OnceLock<Option<String>>,
+    doc_value_cache: Box<OnceLock<Option<Box<str>>>>,
 }
 
 impl Attributes {
-    fn new(doc_strings: Vec<DocFragment>, other_attrs: ThinVec<hir::Attribute>) -> Self {
-        Self { doc_strings, other_attrs, doc_value_cache: OnceLock::new() }
+    fn new(doc_strings: ThinVec<DocFragment>, other_attrs: ThinVec<hir::Attribute>) -> Self {
+        Self { doc_strings, other_attrs, doc_value_cache: Box::new(OnceLock::new()) }
     }
 
     pub(crate) fn doc_strings(&self) -> &[DocFragment] {
@@ -1066,7 +1066,7 @@ impl Attributes {
                         add_doc_fragment(&mut res, frag);
                     }
                     res.pop();
-                    res
+                    res.into_boxed_str()
                 })
             })
             .as_deref()
@@ -2432,7 +2432,7 @@ mod size_asserts {
     static_assert_size!(GenericParamDef, 40);
     static_assert_size!(Generics, 16);
     static_assert_size!(Item, 8);
-    static_assert_size!(ItemInner, 176);
+    static_assert_size!(ItemInner, 136);
     static_assert_size!(ItemKind, 48);
     static_assert_size!(PathSegment, 32);
     static_assert_size!(Type, 32);

src/librustdoc/clean/types/tests.rs

@@ -4,15 +4,15 @@ use rustc_span::create_default_session_globals_then;
 
 use super::*;
 
-fn create_doc_fragment(s: &str) -> Vec<DocFragment> {
-    vec![DocFragment {
+fn create_doc_fragment(s: &str) -> ThinVec<DocFragment> {
+    ThinVec::from([DocFragment {
         span: DUMMY_SP,
         item_id: None,
         doc: Symbol::intern(s),
         kind: DocFragmentKind::Sugared(CommentKind::Line),
         indent: 0,
         from_expansion: false,
-    }]
+    }])
 }
 
 #[track_caller]