Optimize string concatenation in hot paths

crates/rspack_core/src/dependencies_block.rs

@@ -102,10 +102,10 @@ impl AsyncDependenciesBlock {
     Self {
       id: format!(
         "{parent}|dep={}{}{}",
-        dependencies.iter().fold(String::default(), |mut s, dep| {
-          s += dep.resource_identifier().unwrap_or_default();
-          s
-        }),
+        dependencies
+          .iter()
+          .map(|dep| dep.resource_identifier().unwrap_or_default())
+          .collect::<String>(),
         loc_str,
         modifier_str
       )

crates/rspack_core/src/utils/compile_boolean_matcher.rs

@@ -104,11 +104,11 @@ pub(crate) fn items_to_regexp(items_arr: Vec<String>) -> String {
   let mut items = items_arr.iter().cloned().collect::<BTreeSet<_>>();
 
   if count_of_single_char_items > 2 {
-    let mut single_char_items: String = String::new();
+    let mut single_char_items = String::with_capacity(count_of_single_char_items);
     let mut new_items = BTreeSet::new();
     for item in items {
       if item.chars().count() == 1 {
-        single_char_items += &item;
+        single_char_items.push_str(&item);
         continue;
       }
       new_items.insert(item);

crates/rspack_plugin_javascript/src/utils/eval/mod.rs

@@ -278,15 +278,11 @@ impl<'a> BasicEvaluatedExpression<'a> {
       }
       Some(format!("[{}]", arr.join(", ")))
     } else if self.is_template_string() {
-      let mut s = String::new();
-      for p in self.parts() {
-        if let Some(p) = p.as_string() {
-          s += &p;
-        } else {
-          return None;
-        }
-      }
-      Some(s)
+      self
+        .parts()
+        .iter()
+        .map(|p| p.as_string())
+        .collect::<Option<String>>()
     } else {
       None
     }