librustdoc: lazily format some paths

Author: yotamofek

src/librustdoc/html/format.rs

@@ -709,19 +709,22 @@ fn resolved_path(
     if w.alternate() {
         write!(w, "{}{:#}", last.name, last.args.print(cx))?;
     } else {
-        let path = if use_absolute {
-            if let Ok((_, _, fqp)) = href(did, cx) {
-                format!(
-                    "{path}::{anchor}",
-                    path = join_with_double_colon(&fqp[..fqp.len() - 1]),
-                    anchor = anchor(did, *fqp.last().unwrap(), cx)
-                )
+        let path = fmt::from_fn(|f| {
+            if use_absolute {
+                if let Ok((_, _, fqp)) = href(did, cx) {
+                    write!(
+                        f,
+                        "{path}::{anchor}",
+                        path = join_with_double_colon(&fqp[..fqp.len() - 1]),
+                        anchor = anchor(did, *fqp.last().unwrap(), cx)
+                    )
+                } else {
+                    write!(f, "{}", last.name)
+                }
             } else {
-                last.name.to_string()
+                write!(f, "{}", anchor(did, last.name, cx))
             }
-        } else {
-            anchor(did, last.name, cx).to_string()
-        };
+        });
         write!(w, "{path}{args}", args = last.args.print(cx))?;
     }
     Ok(())
@@ -749,16 +752,20 @@ fn primitive_link_fragment(
         match m.primitive_locations.get(&prim) {
             Some(&def_id) if def_id.is_local() => {
                 let len = cx.current.len();
-                let path = if len == 0 {
-                    let cname_sym = ExternalCrate { crate_num: def_id.krate }.name(cx.tcx());
-                    format!("{cname_sym}/")
-                } else {
-                    "../".repeat(len - 1)
-                };
+                let path = fmt::from_fn(|f| {
+                    if len == 0 {
+                        let cname_sym = ExternalCrate { crate_num: def_id.krate }.name(cx.tcx());
+                        write!(f, "{cname_sym}/")?;
+                    } else {
+                        for _ in 0..(len - 1) {
+                            f.write_str("../")?;
+                        }
+                    }
+                    Ok(())
+                });
                 write!(
                     f,
-                    "<a class=\"primitive\" href=\"{}primitive.{}.html{fragment}\">",
-                    path,
+                    "<a class=\"primitive\" href=\"{path}primitive.{}.html{fragment}\">",
                     prim.as_sym()
                 )?;
                 needs_termination = true;

src/librustdoc/html/render/context.rs

@@ -266,12 +266,12 @@ impl<'tcx> Context<'tcx> {
                     // preventing an infinite redirection loop in the generated
                     // documentation.
 
-                    let mut path = String::new();
-                    for name in &names[..names.len() - 1] {
-                        path.push_str(name.as_str());
-                        path.push('/');
-                    }
-                    let _ = write!(path, "{}", item_path(ty, names.last().unwrap().as_str()));
+                    let path = fmt::from_fn(|f| {
+                        for name in &names[..names.len() - 1] {
+                            write!(f, "{name}/")?;
+                        }
+                        write!(f, "{}", item_path(ty, names.last().unwrap().as_str()))
+                    });
                     match self.shared.redirections {
                         Some(ref redirections) => {
                             let mut current_path = String::new();