Support prepend

Author: hyf0

src/chunk.rs

@@ -27,11 +27,16 @@ impl<'s> Chunk<'s> {
         intro_iter.chain(Some(source_frag)).chain(outro_iter)
     }
 
-    pub fn append_outro(&mut self, frag: CowStr<'s>) {
+    pub fn append(&mut self, frag: CowStr<'s>) {
         self.len += frag.len();
         self.outro.push(frag.into())
     }
 
+    pub fn prepend(&mut self, frag: CowStr<'s>) {
+        self.len += frag.len();
+        self.intro.push(frag.into())
+    }
+
     pub fn len(&self) -> usize {
         self.len
     }

src/magic_string.rs

@@ -42,7 +42,12 @@ impl<'s> MagicString<'s> {
     }
 
     pub fn append(&mut self, source: impl Into<CowStr<'s>>) -> &mut Self {
-        self.last_chunk_mut().append_outro(source.into());
+        self.last_chunk_mut().append(source.into());
+        self
+    }
+
+    pub fn prepend(&mut self, source: impl Into<CowStr<'s>>) -> &mut Self {
+        self.first_chunk_mut().prepend(source.into());
         self
     }
 
@@ -99,6 +104,11 @@ impl<'s> MagicString<'s> {
         let idx = self.chunk_by_end.get(&(self.source_len)).unwrap();
         &mut self.chunks[*idx]
     }
+
+    fn first_chunk_mut(&mut self) -> &mut Chunk<'s> {
+        let idx = self.chunk_by_start.get(&0).unwrap();
+        &mut self.chunks[*idx]
+    }
 }
 
 struct ChunkIter<'a> {

tests/magic_string.rs

@@ -28,3 +28,17 @@ mod append {
         assert_eq!(s.to_string(), "abcdefghijklxyzxyz");
     }
 }
+
+mod prepend {
+    use super::*;
+    
+    #[test]
+    fn should_append_content() {
+        // should append content
+        let mut s = MagicString::new("abcdefghijkl");
+        s.prepend("xyz");
+        assert_eq!(s.to_string(), "xyzabcdefghijkl");
+        s.prepend("xyz");
+        assert_eq!(s.to_string(), "xyzxyzabcdefghijkl");
+    }
+}