librustdoc: make item_path formatting lazy

Author: yotamofek

src/librustdoc/html/render/context.rs

@@ -1,5 +1,6 @@
 use std::cell::RefCell;
 use std::collections::BTreeMap;
+use std::fmt::Write as _;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::sync::mpsc::{Receiver, channel};
@@ -267,16 +268,20 @@ impl<'tcx> Context<'tcx> {
                         path.push_str(name.as_str());
                         path.push('/');
                     }
-                    path.push_str(&item_path(ty, names.last().unwrap().as_str()));
+                    let _ = write!(path, "{}", item_path(ty, names.last().unwrap().as_str()));
                     match self.shared.redirections {
                         Some(ref redirections) => {
                             let mut current_path = String::new();
                             for name in &self.current {
                                 current_path.push_str(name.as_str());
                                 current_path.push('/');
                             }
-                            current_path.push_str(&item_path(ty, names.last().unwrap().as_str()));
-                            redirections.borrow_mut().insert(current_path, path);
+                            let _ = write!(
+                                current_path,
+                                "{}",
+                                item_path(ty, names.last().unwrap().as_str())
+                            );
+                            redirections.borrow_mut().insert(current_path, path.to_string());
                         }
                         None => {
                             return layout::redirect(&format!(
@@ -851,9 +856,9 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
         if !buf.is_empty() {
             let name = item.name.as_ref().unwrap();
             let item_type = item.type_();
-            let file_name = &item_path(item_type, name.as_str());
+            let file_name = item_path(item_type, name.as_str()).to_string();
             self.shared.ensure_dir(&self.dst)?;
-            let joint_dst = self.dst.join(file_name);
+            let joint_dst = self.dst.join(&file_name);
             self.shared.fs.write(joint_dst, buf)?;
 
             if !self.info.render_redirect_pages {
@@ -870,7 +875,7 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
                         format!("{crate_name}/{file_name}"),
                     );
                 } else {
-                    let v = layout::redirect(file_name);
+                    let v = layout::redirect(&file_name);
                     let redir_dst = self.dst.join(redir_name);
                     self.shared.fs.write(redir_dst, v)?;
                 }

src/librustdoc/html/render/print_item.rs

@@ -2042,11 +2042,11 @@ pub(super) fn full_path(cx: &Context<'_>, item: &clean::Item) -> String {
     s
 }
 
-pub(super) fn item_path(ty: ItemType, name: &str) -> String {
-    match ty {
-        ItemType::Module => format!("{}index.html", ensure_trailing_slash(name)),
-        _ => format!("{ty}.{name}.html"),
-    }
+pub(super) fn item_path(ty: ItemType, name: &str) -> impl Display + '_ {
+    fmt::from_fn(move |f| match ty {
+        ItemType::Module => write!(f, "{}index.html", ensure_trailing_slash(name)),
+        _ => write!(f, "{ty}.{name}.html"),
+    })
 }
 
 fn bounds<'a, 'tcx>(