perf: replace source (#130)

Author: SyMind

src/concat_source.rs

@@ -100,18 +100,27 @@ impl ConcatSource {
 
 impl Source for ConcatSource {
   fn source(&self) -> Cow<str> {
-    let all = self.children().iter().map(|child| child.source()).collect();
-    Cow::Owned(all)
+    let children = self.children();
+    if children.len() == 1 {
+      children[0].source()
+    } else {
+      let all = self.children().iter().map(|child| child.source()).collect();
+      Cow::Owned(all)
+    }
   }
 
   fn buffer(&self) -> Cow<[u8]> {
-    let all = self
-      .children()
-      .iter()
-      .map(|child| child.buffer())
-      .collect::<Vec<_>>()
-      .concat();
-    Cow::Owned(all)
+    let children = self.children();
+    if children.len() == 1 {
+      children[0].buffer()
+    } else {
+      let all = children
+        .iter()
+        .map(|child| child.buffer())
+        .collect::<Vec<_>>()
+        .concat();
+      Cow::Owned(all)
+    }
   }
 
   fn size(&self) -> usize {

src/helpers.rs

@@ -456,7 +456,7 @@ fn stream_chunks_of_source_map_full<'a>(
           [(current_generated_line - 1) as usize]
           .substring(current_generated_column as usize, usize::MAX);
         on_chunk(
-          Some(Cow::Owned(chunk.to_string())),
+          Some(Cow::Borrowed(chunk)),
           Mapping {
             generated_line: current_generated_line,
             generated_column: current_generated_column,
@@ -472,7 +472,7 @@ fn stream_chunks_of_source_map_full<'a>(
         let chunk =
           line_with_indices_list[(current_generated_line as usize) - 1].line;
         on_chunk(
-          Some(Cow::Owned(chunk.to_string())),
+          Some(Cow::Borrowed(chunk)),
           Mapping {
             generated_line: current_generated_line,
             generated_column: 0,

src/replace_source.rs

@@ -206,8 +206,10 @@ impl<T: Source + Hash + PartialEq + Eq + 'static> Source for ReplaceSource<T> {
   }
 
   fn buffer(&self) -> Cow<[u8]> {
-    let source = self.source().to_string();
-    Cow::Owned(source.into_bytes())
+    match self.source() {
+      Cow::Borrowed(s) => Cow::Borrowed(s.as_bytes()),
+      Cow::Owned(s) => Cow::Owned(s.into_bytes()),
+    }
   }
 
   fn size(&self) -> usize {
@@ -407,10 +409,17 @@ impl<'a, T: Source> StreamChunks<'a> for ReplaceSource<T> {
           if next_replacement_pos > pos {
             // Emit chunk until replacement
             let offset = next_replacement_pos - pos;
-            let chunk_slice =
-              &chunk[chunk_pos as usize..(chunk_pos + offset) as usize];
+            let chunk_slice = match &chunk {
+              Cow::Borrowed(c) => Cow::Borrowed(
+                &c[chunk_pos as usize..(chunk_pos + offset) as usize],
+              ),
+              Cow::Owned(c) => Cow::Owned(
+                c[chunk_pos as usize..(chunk_pos + offset) as usize]
+                  .to_string(),
+              ),
+            };
             on_chunk(
-              Some(Cow::Owned(chunk_slice.to_string())),
+              Some(chunk_slice.clone()),
               Mapping {
                 generated_line: line as u32,
                 generated_column: ((mapping.generated_column as i64)
@@ -440,16 +449,20 @@ impl<'a, T: Source> StreamChunks<'a> for ReplaceSource<T> {
                   original.source_index,
                   original.original_line,
                   original.original_column,
-                  chunk_slice,
+                  &chunk_slice,
                 )
               })
             {
               original.original_column += chunk_slice.len() as u32;
             }
           }
           // Insert replacement content split into chunks by lines
+          #[allow(unsafe_code)]
+          // SAFETY: The safety of this operation relies on the fact that the `ReplaceSource` type will not delete the `replacements` during its entire lifetime.
+          let repl = unsafe {
+            std::mem::transmute::<&Replacement, &'a Replacement>(&repls[i])
+          };
 
-          let repl = &repls[i];
           let lines: Vec<&str> = split_into_lines(&repl.content).collect();
           let mut replacement_name_index = mapping
             .original
@@ -463,14 +476,14 @@ impl<'a, T: Source> StreamChunks<'a> for ReplaceSource<T> {
             if global_index.is_none() {
               let len = name_mapping.len() as u32;
               name_mapping.insert(Cow::Borrowed(name), len);
-              on_name.borrow_mut()(len, Cow::Owned(name.to_string()));
+              on_name.borrow_mut()(len, Cow::Borrowed(name));
               global_index = Some(len);
             }
             replacement_name_index = global_index;
           }
           for (m, content_line) in lines.iter().enumerate() {
             on_chunk(
-              Some(Cow::Owned(content_line.to_string())),
+              Some(Cow::Borrowed(content_line)),
               Mapping {
                 generated_line: line as u32,
                 generated_column: ((mapping.generated_column as i64)
@@ -581,7 +594,10 @@ impl<'a, T: Source> StreamChunks<'a> for ReplaceSource<T> {
           let chunk_slice = if chunk_pos == 0 {
             chunk
           } else {
-            Cow::Owned(chunk[chunk_pos as usize..].to_string())
+            match chunk {
+              Cow::Borrowed(c) => Cow::Borrowed(&c[chunk_pos as usize..]),
+              Cow::Owned(c) => Cow::Owned(c[chunk_pos as usize..].to_string()),
+            }
           };
           let line = mapping.generated_line as i64 + generated_line_offset;
           on_chunk(