WIP: alternate interface for OrderedJson to reduce allocations

Author: lolbinarycat

src/librustdoc/html/render/ordered_json.rs

@@ -32,6 +32,25 @@ 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()
+    }
+
+    pub(crate) fn array_unsorted_serialize<T: Serialize, I: IntoIterator<Item = T>>(items: I) -> Self {
+        let mut out = Vec::with_capacity(1024);
+        let mut add_comma = false;
+        out.push(b'[');
+        for item in items {
+            if add_comma {
+                out.push(b',');
+            }
+            // nothing we serialize should be able to fail to serialize.
+            serde_json::to_writer(&mut out, &item).expect("serialization failed");
+        }
+        out.push(b']');
+        Self(String::from_utf8(out).expect("json was not utf8"))
+    }
 }
 
 impl fmt::Display for OrderedJson {
@@ -79,5 +98,24 @@ impl fmt::Display for EscapedJson {
     }
 }
 
+/// Builds an json array.
+#[derive(Default)]
+pub(crate) struct OrderedJsonBuilder {
+    partial: Vec<u8>,
+}
+
+impl OrderedJsonBuilder {
+    fn push(item: impl Serialize) {
+        if self.partial.is_empty() {
+            self.partial.push('[');
+        } else {
+            self.partial.push(',');
+        }
+        serde_json::to_writer(&mut out, &item).expect("serialization failed");
+    }
+}
+
+
+
 #[cfg(test)]
 mod tests;

src/librustdoc/html/render/search_index.rs

@@ -796,6 +796,7 @@ 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(),

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

@@ -3,7 +3,7 @@
 // type checking. See README.md in this directory for more info.
 
 /* eslint-disable */
-declare global {
+declare global {  
     /** Map from crate name to directory structure, for source view */
     declare var srcIndex: Map<string, rustdoc.Dir>;
     /** Defined and documented in `storage.js` */