make write_section_heading return impl fmt::Display

Author: yotamofek

src/librustdoc/html/render/mod.rs

@@ -1208,29 +1208,29 @@ impl<'a> AssocItemLink<'a> {
     }
 }
 
-pub fn write_section_heading(
-    w: &mut impl fmt::Write,
-    title: &str,
-    id: &str,
-    extra_class: Option<&str>,
-    extra: impl fmt::Display,
-) {
-    let (extra_class, whitespace) = match extra_class {
-        Some(extra) => (extra, " "),
-        None => ("", ""),
-    };
-    write!(
-        w,
-        "<h2 id=\"{id}\" class=\"{extra_class}{whitespace}section-header\">\
+pub fn write_section_heading<'a>(
+    title: &'a str,
+    id: &'a str,
+    extra_class: Option<&'a str>,
+    extra: impl fmt::Display + 'a,
+) -> impl fmt::Display + 'a {
+    fmt::from_fn(move |w| {
+        let (extra_class, whitespace) = match extra_class {
+            Some(extra) => (extra, " "),
+            None => ("", ""),
+        };
+        write!(
+            w,
+            "<h2 id=\"{id}\" class=\"{extra_class}{whitespace}section-header\">\
             {title}\
             <a href=\"#{id}\" class=\"anchor\">§</a>\
          </h2>{extra}",
-    )
-    .unwrap();
+        )
+    })
 }
 
-fn write_impl_section_heading(w: &mut impl fmt::Write, title: &str, id: &str) {
-    write_section_heading(w, title, id, None, "")
+fn write_impl_section_heading<'a>(title: &'a str, id: &'a str) -> impl fmt::Display + 'a {
+    write_section_heading(title, id, None, "")
 }
 
 pub(crate) fn render_all_impls(
@@ -1247,24 +1247,32 @@ pub(crate) fn render_all_impls(
         buf
     };
     if !impls.is_empty() {
-        write_impl_section_heading(&mut w, "Trait Implementations", "trait-implementations");
-        write!(w, "<div id=\"trait-implementations-list\">{impls}</div>").unwrap();
+        write!(
+            w,
+            "{}<div id=\"trait-implementations-list\">{impls}</div>",
+            write_impl_section_heading("Trait Implementations", "trait-implementations")
+        )
+        .unwrap();
     }
 
     if !synthetic.is_empty() {
-        write_impl_section_heading(
-            &mut w,
-            "Auto Trait Implementations",
-            "synthetic-implementations",
-        );
-        w.write_str("<div id=\"synthetic-implementations-list\">").unwrap();
+        write!(
+            w,
+            "{}<div id=\"synthetic-implementations-list\">",
+            write_impl_section_heading("Auto Trait Implementations", "synthetic-implementations",)
+        )
+        .unwrap();
         render_impls(cx, &mut w, synthetic, containing_item, false);
         w.write_str("</div>").unwrap();
     }
 
     if !blanket_impl.is_empty() {
-        write_impl_section_heading(&mut w, "Blanket Implementations", "blanket-implementations");
-        w.write_str("<div id=\"blanket-implementations-list\">").unwrap();
+        write!(
+            w,
+            "{}<div id=\"blanket-implementations-list\">",
+            write_impl_section_heading("Blanket Implementations", "blanket-implementations")
+        )
+        .unwrap();
         render_impls(cx, &mut w, blanket_impl, containing_item, false);
         w.write_str("</div>").unwrap();
     }
@@ -1301,25 +1309,34 @@ fn render_assoc_items_inner(
         let mut tmp_buf = String::new();
         let (render_mode, id, class_html) = match what {
             AssocItemRender::All => {
-                write_impl_section_heading(&mut tmp_buf, "Implementations", "implementations");
+                write_str(
+                    &mut tmp_buf,
+                    format_args!(
+                        "{}",
+                        write_impl_section_heading("Implementations", "implementations")
+                    ),
+                );
                 (RenderMode::Normal, "implementations-list".to_owned(), "")
             }
             AssocItemRender::DerefFor { trait_, type_, deref_mut_ } => {
                 let id =
                     cx.derive_id(small_url_encode(format!("deref-methods-{:#}", type_.print(cx))));
                 let derived_id = cx.derive_id(&id);
-                tmp_buf.push_str("<details class=\"toggle big-toggle\" open><summary>");
                 close_tags.push("</details>");
-                write_impl_section_heading(
+                write_str(
                     &mut tmp_buf,
-                    &format!(
-                        "<span>Methods from {trait_}&lt;Target = {type_}&gt;</span>",
-                        trait_ = trait_.print(cx),
-                        type_ = type_.print(cx),
+                    format_args!(
+                        "<details class=\"toggle big-toggle\" open><summary>{}</summary>",
+                        write_impl_section_heading(
+                            &format!(
+                                "<span>Methods from {trait_}&lt;Target = {type_}&gt;</span>",
+                                trait_ = trait_.print(cx),
+                                type_ = type_.print(cx),
+                            ),
+                            &id,
+                        )
                     ),
-                    &id,
                 );
-                tmp_buf.push_str("</summary>");
                 if let Some(def_id) = type_.def_id(cx.cache()) {
                     cx.deref_id_map.borrow_mut().insert(def_id, id);
                 }