perf: replace source to original (#203)

Author: SyMind

src/cached_source.rs

@@ -87,9 +87,7 @@ impl Source for CachedSource {
   }
 
   fn buffer(&self) -> Cow<[u8]> {
-    let mut buffer = vec![];
-    self.to_writer(&mut buffer).unwrap();
-    Cow::Owned(buffer)
+    self.inner.buffer()
   }
 
   fn size(&self) -> usize {
@@ -116,6 +114,10 @@ impl Source for CachedSource {
     }
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    self.inner.write_to_string(string);
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     self.inner.to_writer(writer)
   }

src/concat_source.rs

@@ -167,11 +167,11 @@ impl Source for ConcatSource {
     if children.len() == 1 {
       children[0].source()
     } else {
-      let mut buf = String::with_capacity(self.size());
-      for child in children {
-        buf.push_str(&child.source().into_string_lossy());
-      }
-      SourceValue::String(Cow::Owned(buf))
+      // Use to_writer to avoid multiple heap allocations that would occur
+      // when concatenating nested ConcatSource instances directly
+      let mut string = String::with_capacity(self.size());
+      self.write_to_string(&mut string);
+      SourceValue::String(Cow::Owned(string))
     }
   }
 
@@ -180,6 +180,8 @@ impl Source for ConcatSource {
     if children.len() == 1 {
       children[0].buffer()
     } else {
+      // Use to_writer to avoid multiple heap allocations that would occur
+      // when concatenating nested ConcatSource instances directly
       let mut buffer = Vec::with_capacity(self.size());
       self.to_writer(&mut buffer).unwrap();
       Cow::Owned(buffer)
@@ -204,6 +206,12 @@ impl Source for ConcatSource {
     result
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    for child in self.optimized_children() {
+      child.write_to_string(string);
+    }
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     for child in self.optimized_children() {
       child.to_writer(writer)?;

src/original_source.rs

@@ -73,6 +73,10 @@ impl Source for OriginalSource {
     get_map(object_pool, chunks.as_ref(), options)
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(self.value.as_ref());
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(self.value.as_bytes())
   }

src/raw_source.rs

@@ -76,6 +76,10 @@ impl Source for RawStringSource {
     None
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(self.0.as_ref());
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(self.0.as_bytes())
   }
@@ -218,6 +222,10 @@ impl Source for RawBufferSource {
     None
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(self.get_or_init_value_as_string());
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(&self.value)
   }

src/replace_source.rs

@@ -12,8 +12,8 @@ use crate::{
   linear_map::LinearMap,
   object_pool::ObjectPool,
   source_content_lines::SourceContentLines,
-  BoxSource, MapOptions, Mapping, OriginalLocation, Source, SourceExt,
-  SourceMap, SourceValue,
+  BoxSource, MapOptions, Mapping, OriginalLocation, OriginalSource, Source,
+  SourceExt, SourceMap, SourceValue,
 };
 
 /// Decorates a Source with replacements and insertions of source code,
@@ -244,6 +244,10 @@ impl Source for ReplaceSource {
     get_map(&ObjectPool::default(), chunks.as_ref(), options)
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(&self.source().into_string_lossy());
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(self.source().as_bytes())
   }
@@ -312,13 +316,17 @@ fn check_content_at_position(
 }
 
 struct ReplaceSourceChunks<'a> {
+  is_original_source: bool,
   chunks: Box<dyn Chunks + 'a>,
   replacements: &'a [Replacement],
 }
 
 impl<'a> ReplaceSourceChunks<'a> {
   pub fn new(source: &'a ReplaceSource) -> Self {
+    let is_original_source =
+      source.inner.as_ref().as_any().is::<OriginalSource>();
     Self {
+      is_original_source,
       chunks: source.inner.stream_chunks(),
       replacements: &source.replacements,
     }
@@ -378,6 +386,13 @@ impl Chunks for ReplaceSourceChunks<'_> {
     // webpack-sources also have this function, refer https://github.com/webpack/webpack-sources/blob/main/lib/ReplaceSource.js#L158
     let check_original_content =
       |source_index: u32, line: u32, column: u32, expected_chunk: &str| {
+        // Performance optimization: Skip content validation for OriginalSourceChunks.
+        // Since OriginalSourceChunks guarantees that the source content matches the actual source,
+        // we can safely bypass the expensive content checking process.
+        if self.is_original_source {
+          return true;
+        }
+
         if let Some(Some(source_content)) =
           source_content_lines.borrow_mut().get_mut(&source_index)
         {

src/source.rs

@@ -132,6 +132,14 @@ pub trait Source:
     self.dyn_hash(state);
   }
 
+  /// Appends the source content to the provided string buffer.
+  ///
+  /// This method efficiently writes the source content directly into an existing
+  /// string buffer, avoiding additional memory allocations when the buffer has
+  /// sufficient capacity. This is particularly useful for concatenating multiple
+  /// sources or building larger strings incrementally.
+  fn write_to_string(&self, string: &mut String);
+
   /// Writes the source into a writer, preferably a `std::io::BufWriter<std::io::Write>`.
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()>;
 }
@@ -157,6 +165,10 @@ impl Source for BoxSource {
     self.as_ref().map(object_pool, options)
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    self.as_ref().write_to_string(string)
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     self.as_ref().to_writer(writer)
   }

src/source_map_source.rs

@@ -114,6 +114,10 @@ impl Source for SourceMapSource {
     get_map(object_pool, chunks.as_ref(), options)
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(self.value.as_ref());
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(self.value.as_bytes())
   }

tests/compat_source.rs

@@ -35,6 +35,10 @@ impl Source for CompatSource {
     self.1.clone()
   }
 
+  fn write_to_string(&self, string: &mut String) {
+    string.push_str(self.0.as_ref())
+  }
+
   fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
     writer.write_all(self.0.as_bytes())
   }