Auto merge of #142634 - lolbinarycat:rustdoc-OrderedJson-writer, r=<try>

alternate interface for OrderedJson to reduce allocations

inspired by #142380 (comment)

r? `@GuillaumeGomez`
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Author: rust-bors[bot]

src/librustdoc/html/render/ordered_json.rs

@@ -32,6 +32,10 @@ impl OrderedJson {
         let items = items.into_iter().format_with(",", |item, f| f(item.borrow()));
         Self(format!("[{items}]"))
     }
+
+    pub(crate) fn array_builder() -> OrderedJsonBuilder {
+        OrderedJsonBuilder::default()
+    }
 }
 
 impl fmt::Display for OrderedJson {
@@ -79,5 +83,32 @@ impl fmt::Display for EscapedJson {
     }
 }
 
+/// Builds an json array.
+#[derive(Default)]
+pub(crate) struct OrderedJsonBuilder {
+    partial: Vec<u8>,
+}
+
+impl OrderedJsonBuilder {
+    pub(crate) fn push(&mut self, item: impl Serialize) -> &mut Self {
+        if self.partial.is_empty() {
+            self.partial.push(b'[');
+        } else {
+            self.partial.push(b',');
+        }
+        serde_json::to_writer(&mut self.partial, &item).expect("serialization failed");
+        self
+    }
+
+    pub(crate) fn build(&mut self) -> OrderedJson {
+        let mut out = std::mem::take(&mut self.partial);
+        if out.is_empty() {
+            return OrderedJson("[]".to_string());
+        }
+        out.push(b']');
+        OrderedJson(String::from_utf8(out).expect("serialization bug: json is invalid utf8"))
+    }
+}
+
 #[cfg(test)]
 mod tests;

src/librustdoc/html/render/search_index.rs

@@ -796,10 +796,8 @@ pub(crate) fn build_index(
         desc_index,
         empty_desc,
     };
-    let index = OrderedJson::array_unsorted([
-        OrderedJson::serialize(crate_name.as_str()).unwrap(),
-        OrderedJson::serialize(data).unwrap(),
-    ]);
+
+    let index = OrderedJson::array_builder().push(crate_name.as_str()).push(data).build();
     SerializedSearchIndex { index, desc }
 }
 

src/librustdoc/html/static/js/rustdoc.d.ts

@@ -129,7 +129,7 @@ declare namespace rustdoc {
 
     /**
      * A single parsed "atom" in a search query. For example,
-     * 
+     *
      *     std::fmt::Formatter, Write -> Result<()>
      *     ┏━━━━━━━━━━━━━━━━━━  ┌────    ┏━━━━━┅┅┅┅┄┄┄┄┄┄┄┄┄┄┄┄┄┄┐
      *     ┃                    │        ┗ QueryElement {        ┊