patch: allow configuring the "No newline at end of file" message

src/diff/tests.rs

@@ -4,6 +4,7 @@ use crate::{
     diff::{Diff, DiffRange},
     patch::Patch,
     range::Range,
+    PatchFormatter,
 };
 
 // Helper macros are based off of the ones used in [dissimilar](https://docs.rs/dissimilar)
@@ -518,6 +519,35 @@ fn no_newline_at_eof() {
     assert_patch!(old, new, expected);
 }
 
+#[test]
+fn without_no_newline_at_eof_message() {
+    let old = "old line";
+    let new = "new line";
+    let expected = "\
+--- original
++++ modified
+@@ -1 +1 @@
+-old line
++new line
+";
+
+    let f = PatchFormatter::new().missing_newline_message(false);
+    let patch = create_patch(old, new);
+    let bpatch = create_patch_bytes(old.as_bytes(), new.as_bytes());
+    let patch_str = format!("{}", f.fmt_patch(&patch));
+    let mut patch_bytes = Vec::new();
+    f.write_patch_into(&bpatch, &mut patch_bytes).unwrap();
+
+    assert_eq!(patch_str, expected);
+    assert_eq!(patch_bytes, patch_str.as_bytes());
+    assert_eq!(patch_bytes, expected.as_bytes());
+    assert_eq!(apply(old, &patch).unwrap(), new);
+    assert_eq!(
+        crate::apply_bytes(old.as_bytes(), &bpatch).unwrap(),
+        new.as_bytes()
+    );
+}
+
 #[test]
 fn myers_diffy_vs_git() {
     let original = "\

src/patch/format.rs

@@ -9,6 +9,7 @@ use std::{
 #[derive(Debug)]
 pub struct PatchFormatter {
     with_color: bool,
+    with_missing_newline_message: bool,
 
     context: Style,
     delete: Style,
@@ -23,6 +24,7 @@ impl PatchFormatter {
     pub fn new() -> Self {
         Self {
             with_color: false,
+            with_missing_newline_message: true,
 
             context: Style::new(),
             delete: Color::Red.normal(),
@@ -39,6 +41,19 @@ impl PatchFormatter {
         self
     }
 
+    /// Sets whether to format a patch with a "No newline at end of file" message.
+    ///
+    /// Default is `true`.
+    ///
+    /// Note: If this is disabled by setting to `false`, formatted patches will no longer contain
+    /// sufficient information to determine if a file ended with a newline character (`\n`) or not
+    /// and the patch will be formatted as if both the original and modified files ended with a
+    /// newline character (`\n`).
+    pub fn missing_newline_message(mut self, enable: bool) -> Self {
+        self.with_missing_newline_message = enable;
+        self
+    }
+
     /// Returns a `Display` impl which can be used to print a Patch
     pub fn fmt_patch<'a>(&'a self, patch: &'a Patch<'a, str>) -> impl Display + 'a {
         PatchDisplay { f: self, patch }
@@ -238,7 +253,9 @@ impl<T: AsRef<[u8]> + ?Sized> LineDisplay<'_, T> {
 
         if !line.ends_with(b"\n") {
             writeln!(w)?;
-            writeln!(w, "{}", NO_NEWLINE_AT_EOF)?;
+            if self.f.with_missing_newline_message {
+                writeln!(w, "{}", NO_NEWLINE_AT_EOF)?;
+            }
         }
 
         Ok(())
@@ -269,7 +286,9 @@ impl Display for LineDisplay<'_, str> {
 
         if !line.ends_with('\n') {
             writeln!(f)?;
-            writeln!(f, "{}", NO_NEWLINE_AT_EOF)?;
+            if self.f.with_missing_newline_message {
+                writeln!(f, "{}", NO_NEWLINE_AT_EOF)?;
+            }
         }
 
         Ok(())