fix: Support reading from files that have an UTF-8 Byte Order Mark

src/file/source/file.rs

@@ -115,7 +115,17 @@ where
             .unwrap_or_else(|| filename.clone());
 
         // Read contents from file
-        let text = fs::read_to_string(filename)?;
+        let buf = fs::read(filename)?;
+
+        // If it exists, skip the UTF-8 BOM byte sequence: EF BB BF
+        let buf = if buf.len() >= 3 && &buf[0..3] == b"\xef\xbb\xbf" {
+            &buf[3..]
+        } else {
+            &buf
+        };
+
+        let c = String::from_utf8_lossy(buf);
+        let text = c.into_owned();
 
         Ok(FileSourceResult {
             uri: Some(uri.to_string_lossy().into_owned()),

tests/testsuite/file-ext-with-bom.json

@@ -0,0 +1,4 @@
+{
+    "debug": true,
+    "production": false
+}

tests/testsuite/file.rs

@@ -67,6 +67,18 @@ fn test_file_ext() {
     assert_eq!(c.get("production").ok(), Some(false));
 }
 
+#[test]
+#[cfg(feature = "json")]
+fn test_file_ext_with_utf8_bom() {
+    let c = Config::builder()
+        .add_source(File::with_name("tests/testsuite/file-ext-with-bom.json"))
+        .build()
+        .unwrap();
+
+    assert_eq!(c.get("debug").ok(), Some(true));
+    assert_eq!(c.get("production").ok(), Some(false));
+}
+
 #[test]
 #[cfg(feature = "json")]
 fn test_file_second_ext() {