feat(common): Add an API to create a SourceFile without allocation (#7029)

crates/swc_common/src/source_map.rs

@@ -202,7 +202,17 @@ impl SourceMap {
 
     /// Creates a new source_file.
     /// This does not ensure that only one SourceFile exists per file name.
-    pub fn new_source_file(&self, filename: FileName, src: String) -> Lrc<SourceFile> {
+    pub fn new_source_file(&self, filename: FileName, mut src: String) -> Lrc<SourceFile> {
+        remove_bom(&mut src);
+
+        self.new_source_file_from(filename, Lrc::new(src))
+    }
+
+    /// Creates a new source_file.
+    /// This does not ensure that only one SourceFile exists per file name.
+    ///
+    /// `src` should not have UTF8 BOM
+    pub fn new_source_file_from(&self, filename: FileName, src: Lrc<String>) -> Lrc<SourceFile> {
         // The path is used to determine the directory for loading submodules and
         // include files, so it must be before remapping.
         // Note that filename may not be a valid path, eg it may be `<anon>` etc,
@@ -224,7 +234,7 @@ impl SourceMap {
 
         let start_pos = self.next_start_pos(src.len());
 
-        let source_file = Lrc::new(SourceFile::new(
+        let source_file = Lrc::new(SourceFile::new_from(
             filename,
             was_remapped,
             unmapped_path,

crates/swc_common/src/syntax_pos.rs

@@ -869,6 +869,25 @@ impl SourceFile {
         unmapped_path: FileName,
         mut src: String,
         start_pos: BytePos,
+    ) -> SourceFile {
+        remove_bom(&mut src);
+
+        Self::new_from(
+            name,
+            name_was_remapped,
+            unmapped_path,
+            Lrc::new(src),
+            start_pos,
+        )
+    }
+
+    /// `src` should not have UTF8 BOM
+    pub fn new_from(
+        name: FileName,
+        name_was_remapped: bool,
+        unmapped_path: FileName,
+        src: Lrc<String>,
+        start_pos: BytePos,
     ) -> SourceFile {
         debug_assert_ne!(
             start_pos,
@@ -876,8 +895,6 @@ impl SourceFile {
             "BytePos::DUMMY is reserved and `SourceFile` should not use it"
         );
 
-        remove_bom(&mut src);
-
         let src_hash = {
             let mut hasher: StableHasher = StableHasher::new();
             hasher.write(src.as_bytes());
@@ -898,7 +915,7 @@ impl SourceFile {
             name_was_remapped,
             unmapped_path: Some(unmapped_path),
             crate_of_origin: 0,
-            src: Lrc::new(src),
+            src,
             src_hash,
             start_pos,
             end_pos: Pos::from_usize(end_pos),
@@ -988,7 +1005,7 @@ impl SourceFile {
 }
 
 /// Remove utf-8 BOM if any.
-fn remove_bom(src: &mut String) {
+pub(super) fn remove_bom(src: &mut String) {
     if src.starts_with('\u{feff}') {
         src.drain(..3);
     }