1 files changed, 47 insertions, 7 deletions

diff --git a/cli/fmt.rs b/cli/fmt.rs
index 9b6e5975d..c297f042c 100644
--- a/cli/fmt.rs
+++ b/cli/fmt.rs
@@ -21,6 +21,8 @@ use std::path::PathBuf;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex};
 
+const BOM_CHAR: char = '\u{FEFF}';
+
 /// Format JavaScript/TypeScript files.
 ///
 /// First argument supports globs, and if it is `None`
@@ -66,11 +68,11 @@ async fn check_source_files(
   run_parallelized(paths, {
     let not_formatted_files_count = not_formatted_files_count.clone();
     move |file_path| {
-      let file_contents = fs::read_to_string(&file_path)?;
-      let r = formatter.format_text(&file_path, &file_contents);
+      let file_text = read_file_contents(&file_path)?.text;
+      let r = formatter.format_text(&file_path, &file_text);
       match r {
         Ok(formatted_text) => {
-          if formatted_text != file_contents {
+          if formatted_text != file_text {
             not_formatted_files_count.fetch_add(1, Ordering::SeqCst);
           }
         }
@@ -112,12 +114,18 @@ async fn format_source_files(
   run_parallelized(paths, {
     let formatted_files_count = formatted_files_count.clone();
     move |file_path| {
-      let file_contents = fs::read_to_string(&file_path)?;
-      let r = formatter.format_text(&file_path, &file_contents);
+      let file_contents = read_file_contents(&file_path)?;
+      let r = formatter.format_text(&file_path, &file_contents.text);
       match r {
         Ok(formatted_text) => {
-          if formatted_text != file_contents {
-            fs::write(&file_path, formatted_text)?;
+          if formatted_text != file_contents.text {
+            write_file_contents(
+              &file_path,
+              FileContents {
+                had_bom: file_contents.had_bom,
+                text: formatted_text,
+              },
+            )?;
             formatted_files_count.fetch_add(1, Ordering::SeqCst);
             let _g = output_lock.lock().unwrap();
             println!("{}", file_path.to_string_lossy());
@@ -203,6 +211,38 @@ fn get_config() -> dprint::configuration::Configuration {
   ConfigurationBuilder::new().deno().build()
 }
 
+struct FileContents {
+  text: String,
+  had_bom: bool,
+}
+
+fn read_file_contents(file_path: &PathBuf) -> Result<FileContents, ErrBox> {
+  let file_text = fs::read_to_string(&file_path)?;
+  let had_bom = file_text.starts_with(BOM_CHAR);
+  let text = if had_bom {
+    // remove the BOM
+    String::from(&file_text[BOM_CHAR.len_utf8()..])
+  } else {
+    file_text
+  };
+
+  Ok(FileContents { text, had_bom })
+}
+
+fn write_file_contents(
+  file_path: &PathBuf,
+  file_contents: FileContents,
+) -> Result<(), ErrBox> {
+  let file_text = if file_contents.had_bom {
+    // add back the BOM
+    format!("{}{}", BOM_CHAR, file_contents.text)
+  } else {
+    file_contents.text
+  };
+
+  Ok(fs::write(file_path, file_text)?)
+}
+
 async fn run_parallelized<F>(
   file_paths: Vec<PathBuf>,
   f: F,