perf: reduce alloc for bailout reason

crates/rspack_core/src/external_module.rs

@@ -349,14 +349,11 @@ impl Module for ExternalModule {
     &self,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
+  ) -> Option<Cow<'static, str>> {
     match self.external_type.as_ref() {
       "amd" | "umd" | "amd-require" | "umd2" | "system" | "jsonp" => {
         // return `${this.externalType} externals can't be concatenated`;
-        Some(format!(
-          "{} externals can't be concatenated",
-          self.external_type
-        ))
+        Some(format!("{} externals can't be concatenated", self.external_type).into())
       }
       _ => None,
     }

crates/rspack_core/src/module.rs

@@ -318,11 +318,14 @@ pub trait Module:
     &self,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
-    Some(format!(
-      "Module Concatenation is not implemented for {}",
-      self.module_type()
-    ))
+  ) -> Option<Cow<'static, str>> {
+    Some(
+      format!(
+        "Module Concatenation is not implemented for {}",
+        self.module_type()
+      )
+      .into(),
+    )
   }
 
   /// Resolve options matched by module rules.

crates/rspack_core/src/normal_module.rs

@@ -689,7 +689,11 @@ impl Module for NormalModule {
     ConnectionState::Bool(true)
   }
 
-  fn get_concatenation_bailout_reason(&self, mg: &ModuleGraph, cg: &ChunkGraph) -> Option<String> {
+  fn get_concatenation_bailout_reason(
+    &self,
+    mg: &ModuleGraph,
+    cg: &ChunkGraph,
+  ) -> Option<Cow<'static, str>> {
     self
       .parser_and_generator
       .get_concatenation_bailout_reason(self, mg, cg)

crates/rspack_core/src/parser_and_generator.rs

@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::borrow::Cow;
 use std::fmt::Debug;
 
 use derivative::Derivative;
@@ -102,7 +103,7 @@ pub trait ParserAndGenerator: Send + Sync + Debug + AsAny {
     _module: &dyn Module,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String>;
+  ) -> Option<Cow<'static, str>>;
 }
 
 impl dyn ParserAndGenerator + '_ {

crates/rspack_plugin_asset/src/lib.rs

@@ -1,6 +1,6 @@
 #![feature(let_chains)]
 
-use std::hash::Hasher;
+use std::{borrow::Cow, hash::Hasher};
 
 use async_trait::async_trait;
 use rayon::prelude::*;
@@ -457,7 +457,7 @@ impl ParserAndGenerator for AssetParserAndGenerator {
     _module: &dyn rspack_core::Module,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
+  ) -> Option<Cow<'static, str>> {
     None
   }
 }

crates/rspack_plugin_css/src/parser_and_generator/mod.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use indexmap::{IndexMap, IndexSet};
 use once_cell::sync::Lazy;
 use regex::Regex;
@@ -479,10 +481,8 @@ impl ParserAndGenerator for CssParserAndGenerator {
     _module: &dyn rspack_core::Module,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
-    Some(String::from(
-      "Module Concatenation is not implemented for CssParserAndGenerator",
-    ))
+  ) -> Option<Cow<'static, str>> {
+    Some("Module Concatenation is not implemented for CssParserAndGenerator".into())
   }
 }
 

crates/rspack_plugin_javascript/src/parser_and_generator/mod.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::sync::Arc;
 
 use itertools::Itertools;
@@ -329,15 +330,15 @@ impl ParserAndGenerator for JavaScriptParserAndGenerator {
     module: &dyn rspack_core::Module,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
+  ) -> Option<Cow<'static, str>> {
     // Only harmony modules are valid for optimization
     if module.build_meta().is_none()
       || module
         .build_meta()
         .map(|meta| meta.exports_type != BuildMetaExportsType::Namespace)
         .unwrap_or_default()
     {
-      return Some(String::from("Module is not an ECMAScript module"));
+      return Some("Module is not an ECMAScript module".into());
     }
 
     if let Some(deps) = module.get_presentational_dependencies() {
@@ -348,16 +349,16 @@ impl ParserAndGenerator for JavaScriptParserAndGenerator {
           .downcast_ref::<HarmonyCompatibilityDependency>()
           .is_some()
       }) {
-        return Some(String::from("Module is not an ECMAScript module"));
+        return Some("Module is not an ECMAScript module".into());
       }
     } else {
-      return Some(String::from("Module is not an ECMAScript module"));
+      return Some("Module is not an ECMAScript module".into());
     }
 
     if let Some(info) = module.build_info()
       && let Some(bailout) = info.module_concatenation_bailout.as_deref()
     {
-      return Some(format!("Module uses {bailout}",));
+      return Some(format!("Module uses {bailout}").into());
     }
     None
   }

crates/rspack_plugin_javascript/src/plugin/module_concatenation_plugin.rs

@@ -1,4 +1,5 @@
 #![allow(clippy::only_used_in_recursion)]
+use std::borrow::Cow;
 use std::collections::hash_map::DefaultHasher;
 use std::collections::VecDeque;
 use std::hash::Hasher;
@@ -98,7 +99,7 @@ impl ConcatConfiguration {
 #[plugin]
 #[derive(Debug, Default)]
 pub struct ModuleConcatenationPlugin {
-  bailout_reason_map: FxDashMap<ModuleIdentifier, String>,
+  bailout_reason_map: FxDashMap<ModuleIdentifier, Cow<'static, str>>,
 }
 
 impl ModuleConcatenationPlugin {
@@ -128,13 +129,18 @@ impl ModuleConcatenationPlugin {
     }
   }
 
-  fn set_bailout_reason(&self, module: &ModuleIdentifier, reason: String, mg: &mut ModuleGraph) {
+  fn set_bailout_reason(
+    &self,
+    module: &ModuleIdentifier,
+    reason: Cow<'static, str>,
+    mg: &mut ModuleGraph,
+  ) {
     self.set_inner_bailout_reason(module, reason.clone());
     mg.get_optimization_bailout_mut(module)
       .push(format_bailout_reason(&reason));
   }
 
-  fn set_inner_bailout_reason(&self, module: &ModuleIdentifier, reason: String) {
+  fn set_inner_bailout_reason(&self, module: &ModuleIdentifier, reason: Cow<'static, str>) {
     self.bailout_reason_map.insert(*module, reason);
   }
 
@@ -145,7 +151,7 @@ impl ModuleConcatenationPlugin {
     dashmap::mapref::one::Ref<
       '_,
       rspack_identifier::Identifier,
-      String,
+      Cow<'static, str>,
       std::hash::BuildHasherDefault<rustc_hash::FxHasher>,
     >,
   > {
@@ -578,7 +584,7 @@ impl ModuleConcatenationPlugin {
           .is_async(&module_id)
           .expect("should have async result")
         {
-          bailout_reason.push("Module is async".to_string());
+          bailout_reason.push("Module is async".into());
           return (false, false, module_id, bailout_reason);
         }
 
@@ -587,11 +593,11 @@ impl ModuleConcatenationPlugin {
           .expect("should have build info")
           .strict
         {
-          bailout_reason.push("Module is not in strict mode".to_string());
+          bailout_reason.push("Module is not in strict mode".into());
           return (false, false, module_id, bailout_reason);
         }
         if number_of_module_chunks == 0 {
-          bailout_reason.push("Module is not in any chunk".to_string());
+          bailout_reason.push("Module is not in any chunk".into());
           return (false, false, module_id, bailout_reason);
         }
 
@@ -626,9 +632,10 @@ impl ModuleConcatenationPlugin {
           //   &mut module_graph,
           // );
 
-          bailout_reason.push(format!(
-            "Reexports in this module do not have a static target ({cur_bailout_reason})"
-          ));
+          bailout_reason.push(
+            format!("Reexports in this module do not have a static target ({cur_bailout_reason})")
+              .into(),
+          );
 
           return (false, false, module_id, bailout_reason);
         }
@@ -665,9 +672,8 @@ impl ModuleConcatenationPlugin {
           //   format!("List of module exports is dynamic ({bailout_reason})"),
           //   &mut module_graph,
           // );
-          bailout_reason.push(format!(
-            "List of module exports is dynamic ({cur_bailout_reason})"
-          ));
+          bailout_reason
+            .push(format!("List of module exports is dynamic ({cur_bailout_reason})").into());
           can_be_root = false;
         }
 
@@ -678,7 +684,7 @@ impl ModuleConcatenationPlugin {
           //   &mut module_graph,
           // );
           can_be_inner = false;
-          bailout_reason.push("Module is an entry point".to_string());
+          bailout_reason.push("Module is an entry point".into());
         }
         (can_be_root, can_be_inner, module_id, bailout_reason)
         // if can_be_root {

crates/rspack_plugin_json/src/lib.rs

@@ -199,7 +199,7 @@ impl ParserAndGenerator for JsonParserAndGenerator {
     _module: &dyn Module,
     _mg: &ModuleGraph,
     _cg: &ChunkGraph,
-  ) -> Option<String> {
+  ) -> Option<Cow<'static, str>> {
     None
   }
 }

crates/rspack_plugin_wasm/src/parser_and_generator.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 
@@ -288,10 +289,8 @@ impl ParserAndGenerator for AsyncWasmParserAndGenerator {
     _module: &dyn Module,
     _mg: &rspack_core::ModuleGraph,
     _cg: &rspack_core::ChunkGraph,
-  ) -> Option<String> {
-    Some(String::from(
-      "Module Concatenation is not implemented for AsyncWasmParserAndGenerator",
-    ))
+  ) -> Option<Cow<'static, str>> {
+    Some("Module Concatenation is not implemented for AsyncWasmParserAndGenerator".into())
   }
 }