feat: add to_writer api to Source trait for better file write performance

closes #41

Author: Boshen

src/cached_source.rs

@@ -96,6 +96,10 @@ impl<T: Source + Hash + PartialEq + Eq + 'static> Source for CachedSource<T> {
       map
     }
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    self.inner.to_writer(writer)
+  }
 }
 
 impl<T: Source + Hash + PartialEq + Eq + 'static> StreamChunks

src/concat_source.rs

@@ -99,6 +99,13 @@ impl Source for ConcatSource {
   fn map(&self, options: &MapOptions) -> Option<SourceMap> {
     get_map(self, options)
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    for child in &self.children {
+      child.to_writer(writer)?;
+    }
+    Ok(())
+  }
 }
 
 impl Hash for ConcatSource {

src/original_source.rs

@@ -66,6 +66,10 @@ impl Source for OriginalSource {
   fn map(&self, options: &MapOptions) -> Option<SourceMap> {
     get_map(self, options)
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    writer.write_all(self.value.as_bytes())
+  }
 }
 
 impl Hash for OriginalSource {

src/raw_source.rs

@@ -88,6 +88,13 @@ impl Source for RawSource {
   fn map(&self, _: &MapOptions) -> Option<SourceMap> {
     None
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    writer.write_all(match self {
+      RawSource::Buffer(i) => i,
+      RawSource::Source(i) => i.as_bytes(),
+    })
+  }
 }
 
 impl Hash for RawSource {

src/replace_source.rs

@@ -141,6 +141,10 @@ impl<T: Source + Hash + PartialEq + Eq + 'static> Source for ReplaceSource<T> {
     drop(replacements);
     get_map(self, options)
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    writer.write_all(self.source().as_bytes())
+  }
 }
 
 impl<T: Source> StreamChunks for ReplaceSource<T> {

src/source.rs

@@ -37,6 +37,9 @@ pub trait Source:
   fn update_hash(&self, state: &mut dyn Hasher) {
     self.dyn_hash(state);
   }
+
+  /// 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<()>;
 }
 
 impl Source for Box<dyn Source> {
@@ -55,6 +58,10 @@ impl Source for Box<dyn Source> {
   fn map(&self, options: &MapOptions) -> Option<SourceMap> {
     self.as_ref().map(options)
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    self.as_ref().to_writer(writer)
+  }
 }
 
 dyn_clone::clone_trait_object!(Source);
@@ -615,4 +622,17 @@ mod tests {
     map.insert(a, a);
     assert_eq!(map.get(&a).unwrap(), &a);
   }
+
+  #[test]
+  fn to_writer() {
+    let sources =
+      ConcatSource::new([RawSource::from("a"), RawSource::from("b")]);
+    let mut writer = std::io::BufWriter::new(Vec::new());
+    let result = sources.to_writer(&mut writer);
+    assert!(result.is_ok());
+    assert_eq!(
+      String::from_utf8(writer.into_inner().unwrap()).unwrap(),
+      "ab"
+    );
+  }
 }

src/source_map_source.rs

@@ -106,6 +106,10 @@ impl Source for SourceMapSource {
     }
     get_map(self, options)
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    writer.write_all(self.value.as_bytes())
+  }
 }
 
 impl Hash for SourceMapSource {

tests/compat_source.rs

@@ -27,6 +27,10 @@ impl Source for CompatSource {
   fn map(&self, _options: &MapOptions) -> Option<SourceMap> {
     self.1.clone()
   }
+
+  fn to_writer(&self, writer: &mut dyn std::io::Write) -> std::io::Result<()> {
+    writer.write_all(self.0.as_bytes())
+  }
 }
 
 impl StreamChunks for CompatSource {