diff: pad last newline by show_color_words_diff_line()

Though this is needed only for the last line, checking it for each line is
cheap. As I'm going to add another rendering style, the condition to pad "\n"
would become more complicated.

cli/src/diff_util.rs

@@ -429,48 +429,42 @@ fn show_color_words_diff_hunks(
     let line_diff = Diff::by_line([left, right]);
     let mut line_diff_hunks = line_diff.hunks().peekable();
     let mut line_number = DiffLineNumber { left: 1, right: 1 };
-    // Have we printed "..." for the last skipped context?
-    let mut skipped_context = false;
 
     // First "before" context
     if let Some(DiffHunk::Matching(content)) =
         line_diff_hunks.next_if(|hunk| matches!(hunk, DiffHunk::Matching(_)))
     {
         if line_diff_hunks.peek().is_some() {
-            let (new_line_number, _) = show_color_words_context_lines(
+            line_number = show_color_words_context_lines(
                 formatter,
                 content,
                 line_number,
                 0,
                 options.context,
             )?;
-            line_number = new_line_number;
         }
     }
     while let Some(hunk) = line_diff_hunks.next() {
         match hunk {
             // Middle "after"/"before" context
             DiffHunk::Matching(content) if line_diff_hunks.peek().is_some() => {
-                let (new_line_number, _) = show_color_words_context_lines(
+                line_number = show_color_words_context_lines(
                     formatter,
                     content,
                     line_number,
                     options.context,
                     options.context,
                 )?;
-                line_number = new_line_number;
             }
             // Last "after" context
             DiffHunk::Matching(content) => {
-                let (new_line_number, skipped) = show_color_words_context_lines(
+                line_number = show_color_words_context_lines(
                     formatter,
                     content,
                     line_number,
                     options.context,
                     0,
                 )?;
-                line_number = new_line_number;
-                skipped_context = skipped;
             }
             DiffHunk::Different(contents) => {
                 let word_diff = Diff::by_word(&contents);
@@ -484,13 +478,6 @@ fn show_color_words_diff_hunks(
         }
     }
 
-    // If the last diff line doesn't end with newline, add it.
-    let no_hunk = left.is_empty() && right.is_empty();
-    let any_last_newline = left.ends_with(b"\n") || right.ends_with(b"\n");
-    if !skipped_context && !no_hunk && !any_last_newline {
-        writeln!(formatter)?;
-    }
-
     Ok(())
 }
 
@@ -501,7 +488,7 @@ fn show_color_words_context_lines(
     mut line_number: DiffLineNumber,
     num_after: usize,
     num_before: usize,
-) -> io::Result<(DiffLineNumber, bool)> {
+) -> io::Result<DiffLineNumber> {
     const SKIPPED_CONTEXT_LINE: &str = "    ...\n";
     let mut lines = content.split_inclusive(|b| *b == b'\n').fuse();
     for line in lines.by_ref().take(num_after) {
@@ -530,7 +517,7 @@ fn show_color_words_context_lines(
         line_number.left += 1;
         line_number.right += 1;
     }
-    Ok((line_number, num_skipped > 0))
+    Ok(line_number)
 }
 
 fn show_color_words_line_number(
@@ -584,7 +571,10 @@ fn show_color_words_diff_line(
             formatter.write_all(data)?;
         }
     }
-
+    let (_, data) = diff_line.hunks.last().expect("diff line must not be empty");
+    if !data.ends_with(b"\n") {
+        writeln!(formatter)?;
+    };
     Ok(())
 }