Flush line buffers in additional locations

src/handlers/diff_header.rs

@@ -83,6 +83,7 @@ impl<'a> StateMachine<'a> {
                 ));
         }
 
+        self.painter.paint_buffered_minus_and_plus_lines();
         // In color_only mode, raw_line's structure shouldn't be changed.
         // So it needs to avoid fn _handle_diff_header_header_line
         // (it connects the plus_file and minus_file),
@@ -127,6 +128,7 @@ impl<'a> StateMachine<'a> {
             ));
         self.current_file_pair = Some((self.minus_file.clone(), self.plus_file.clone()));
 
+        self.painter.paint_buffered_minus_and_plus_lines();
         // In color_only mode, raw_line's structure shouldn't be changed.
         // So it needs to avoid fn _handle_diff_header_header_line
         // (it connects the plus_file and minus_file),

src/paint.rs

@@ -126,6 +126,9 @@ impl<'p> Painter<'p> {
     }
 
     pub fn paint_buffered_minus_and_plus_lines(&mut self) {
+        if self.minus_lines.is_empty() && self.plus_lines.is_empty() {
+            return;
+        }
         paint_minus_and_plus_lines(
             MinusPlus::new(&self.minus_lines, &self.plus_lines),
             &mut self.line_numbers_data,

src/tests/test_example_diffs.rs

@@ -135,6 +135,15 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_diff_unified_concatenated() {
+        // See #1002. Line buffers were not being flushed correctly, leading to material from first
+        // file last hunk appearing at beginning of second file first hunk.
+        DeltaTest::with_args(&[])
+            .with_input(DIFF_UNIFIED_CONCATENATED)
+            .expect_contains("\nLINES.\n\n1/y 2022-03-06");
+    }
+
     #[test]
     #[ignore] // Ideally, delta would make this test pass. See #121.
     fn test_delta_ignores_non_diff_input() {
@@ -1875,6 +1884,27 @@ Only in b/: just_b
 +This is different from a
 ";
 
+    const DIFF_UNIFIED_CONCATENATED: &str = "\
+--- 1/x 2022-03-06 11:16:06.313403500 -0800
++++ 2/x 2022-03-06 11:18:14.083403500 -0800
+@@ -1,5 +1,5 @@
+ This
+-is
++IS
+ a
+ few
+-lines.
++LINES.
+--- 1/y 2022-03-06 11:16:44.483403500 -0800
++++ 2/y 2022-03-06 11:16:55.213403500 -0800
+@@ -1,4 +1,4 @@
+ This
+ is
+-another
++ANOTHER
+ test.
+";
+
     const NOT_A_DIFF_OUTPUT: &str = "\
 Hello world
 This is a regular file that contains: