add a newline inside format_single_file not format_string

this is because a standalone string might not be the content of a
file, so we do not want to always add a newline.

src/formatting.rs

@@ -104,7 +104,6 @@ pub(crate) fn format_inner(contents: &[u8], _config: &Config) -> Vec<u8> {
 
  start = span.end + 1;
  }
- out = add_newline_at_end_of_file(out);
 
  out
 }
@@ -116,7 +115,7 @@ fn insert_newline(mut bytes: Vec<u8>) -> Vec<u8> {
 }
 
 /// make sure there is a newline at the end of a buffer
-fn add_newline_at_end_of_file(out: Vec<u8>) -> Vec<u8> {
+pub(crate) fn add_newline_at_end_of_file(out: Vec<u8>) -> Vec<u8> {
  match out.last() {
  Some(&b'\n') => out,
  _ => insert_newline(out),

src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! It does not do anything more than that, which makes it so fast.
 use config::Config;
-use formatting::format_inner;
+use formatting::{add_newline_at_end_of_file, format_inner};
 use log::{debug, trace};
 use std::fs::File;
 use std::io::Write;
@@ -16,7 +16,7 @@ pub fn format_single_file(file: &PathBuf, config: &Config) {
  let contents = std::fs::read(file)
  .unwrap_or_else(|_| panic!("something went wrong reading the file {}", file.display()));
 
- let formatted_bytes = format_inner(&contents, config);
+ let formatted_bytes = add_newline_at_end_of_file(format_inner(&contents, config));
 
  if formatted_bytes == contents {
  debug!("File is formatted correctly.");