Fix headers of modified binary files, closes #1621 (#1629)

3 files changed, 32 insertions, 17 deletions

diff --git a/src/handlers/diff_header.rs b/src/handlers/diff_header.rs
index 334ca76..3c71a61 100644
--- a/src/handlers/diff_header.rs
+++ b/src/handlers/diff_header.rs
@@ -357,7 +357,7 @@ fn parse_diff_header_line(line: &str, git_diff_name: bool) -> (String, FileEvent
 
 /// Given input like "diff --git a/src/my file.rs b/src/my file.rs"
 /// return Some("src/my file.rs")
-fn get_repeated_file_path_from_diff_line(line: &str) -> Option<String> {
+pub fn get_repeated_file_path_from_diff_line(line: &str) -> Option<String> {
     if let Some(line) = line.strip_prefix("diff --git ") {
         let line: Vec<&str> = line.graphemes(true).collect();
         let midpoint = line.len() / 2;
diff --git a/src/handlers/diff_header_diff.rs b/src/handlers/diff_header_diff.rs
index a79f6e1..f8a007e 100644
--- a/src/handlers/diff_header_diff.rs
+++ b/src/handlers/diff_header_diff.rs
@@ -1,4 +1,5 @@
 use crate::delta::{DiffType, InMergeConflict, MergeParents, State, StateMachine};
+use crate::handlers::diff_header::{get_repeated_file_path_from_diff_line, FileEvent};
 
 impl<'a> StateMachine<'a> {
     #[inline]
@@ -25,6 +26,19 @@ impl<'a> StateMachine<'a> {
         self.handle_pending_line_with_diff_name()?;
         self.handled_diff_header_header_line_file_pair = None;
         self.diff_line = self.line.clone();
+
+        // Pre-fill header fields from the diff line. For added, removed or renamed files
+        // these are updated precisely on actual header minus and header plus lines.
+        // But for modified binary files which are not added, removed or renamed, there
+        // are no minus and plus lines. Without the code below, in such cases the file names
+        // would remain unchanged from the previous diff, or empty for the very first diff.
+        let name = get_repeated_file_path_from_diff_line(&self.line).unwrap_or_default();
+        self.minus_file = name.clone();
+        self.plus_file = name.clone();
+        self.minus_file_event = FileEvent::Change;
+        self.plus_file_event = FileEvent::Change;
+        self.current_file_pair = Some((self.minus_file.clone(), self.plus_file.clone()));
+
         if !self.should_skip_line() {
             self.emit_line_unchanged()?;
         }
diff --git a/src/handlers/diff_header_misc.rs b/src/handlers/diff_header_misc.rs
index 141767a..c5e4026 100644
--- a/src/handlers/diff_header_misc.rs
+++ b/src/handlers/diff_header_misc.rs
@@ -12,25 +12,26 @@ impl<'a> StateMachine<'a> {
     }
 
     pub fn handle_diff_header_misc_line(&mut self) -> std::io::Result<bool> {
-        let is_binary: bool = self.test_diff_is_binary();
-        let file_missing: bool = self.test_diff_file_missing();
-
-        if !file_missing && !is_binary {
+        if !self.test_diff_file_missing() && !self.test_diff_is_binary() {
             return Ok(false);
         }
 
-        if is_binary {
-            match (self.minus_file.as_str(), self.plus_file.as_str()) {
-                ("", "") => {
-                    return self.handle_additional_cases(match self.state {
-                        State::DiffHeader(_) => self.state.clone(),
-                        _ => State::DiffHeader(DiffType::Unified),
-                    });
-                }
-                ("/dev/null", _) => self.plus_file.push_str(" (binary file)"),
-                (_, "/dev/null") => self.minus_file.push_str(" (binary file)"),
-                (_, _) => (),
-            };
+        if self.test_diff_is_binary() {
+            // Print the "Binary files" line verbatim, if there was no "diff" line, or it
+            // listed different files but was not followed by header minus and plus lines.
+            // This can happen in output of standalone diff or git diff --no-index.
+            if self.minus_file.is_empty() && self.plus_file.is_empty() {
+                self.emit_line_unchanged()?;
+                self.handled_diff_header_header_line_file_pair = self.current_file_pair.clone();
+                return Ok(true);
+            }
+
+            if self.minus_file != "/dev/null" {
+                self.minus_file.push_str(" (binary file)");
+            }
+            if self.plus_file != "/dev/null" {
+                self.plus_file.push_str(" (binary file)");
+            }
             return Ok(true);
         }