fix(git): synthesize diff line sigils in patches

crates/code2prompt-core/src/git.rs

@@ -11,6 +11,28 @@ use log::info;
 use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 
+/// Synthesize a diff-line sigil (`+`/`-`/` `) for added/removed/context lines.
+///
+/// `git2`'s `DiffFormat::Patch` splits the sigil from the line content:
+/// - `origin()` returns `'+'` / `'-'` / `' '` for added/removed/context lines
+/// - `content()` returns ONLY the raw line text WITHOUT the sigil
+/// - file headers (`'F'`), hunk headers (`'H'`), binary notices (`'B'`) and the
+///   end-of-file markers (`'='/'>'/'<'`) already contain their full text in
+///   `content()`, so they get no synthesized sigil.
+///
+/// `content()` is appended unconditionally, so binary notices and the
+/// `\ No newline at end of file` markers are preserved rather than dropped.
+pub fn write_diff_line(buf: &mut Vec<u8>, origin: char, content: &[u8]) {
+    match origin {
+        '+' => buf.push(b'+'),
+        '-' => buf.push(b'-'),
+        ' ' => buf.push(b' '),
+        'F' | 'H' | 'B' | '=' | '>' | '<' => {} // full text already in content()
+        _ => {}
+    }
+    buf.extend_from_slice(content);
+}
+
 /// Extract git diff for staged changes in repository.
 /// 
 /// Generates diff between HEAD and index to show staged changes, with additional
@@ -50,7 +72,7 @@ pub fn get_git_diff(repo_path: &Path) -> Result<String> {
     let mut staged_diff_text = Vec::new();
     staged_diff
         .print(git2::DiffFormat::Patch, |_delta, _hunk, line| {
-            staged_diff_text.extend_from_slice(line.content());
+            write_diff_line(&mut staged_diff_text, line.origin(), line.content());
             true
         })
         .context("Failed to print staged diff")?;
@@ -70,7 +92,7 @@ pub fn get_git_diff(repo_path: &Path) -> Result<String> {
     let mut unstaged_diff_text = Vec::new();
     unstaged_diff
         .print(git2::DiffFormat::Patch, |_delta, _hunk, line| {
-            unstaged_diff_text.extend_from_slice(line.content());
+            write_diff_line(&mut unstaged_diff_text, line.origin(), line.content());
             true
         })
         .context("Failed to print unstaged diff")?;
@@ -127,7 +149,7 @@ pub fn get_git_diff_between_branches(
 
     let mut diff_text = Vec::new();
     diff.print(git2::DiffFormat::Patch, |_delta, _hunk, line| {
-        diff_text.extend_from_slice(line.content());
+        write_diff_line(&mut diff_text, line.origin(), line.content());
         true
     })
     .context("Failed to print diff")?;

crates/code2prompt-core/tests/git_test.rs

@@ -1,4 +1,6 @@
-use code2prompt_core::git::{get_git_diff, get_git_diff_between_branches, get_git_log};
+use code2prompt_core::git::{
+    get_git_diff, get_git_diff_between_branches, get_git_log, write_diff_line,
+};
 
 #[cfg(test)]
 mod tests {
@@ -385,4 +387,46 @@ mod tests {
             .to_string()
             .contains("Branch nonexistent_reference doesn't exist!"));
     }
+
+    #[test]
+    fn write_diff_line_synthesizes_sigils_for_content_lines() {
+        let mut buf = Vec::new();
+        write_diff_line(&mut buf, '+', b"hello\n");
+        assert_eq!(buf, b"+hello\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, '-', b"world\n");
+        assert_eq!(buf, b"-world\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, ' ', b"ctx\n");
+        assert_eq!(buf, b" ctx\n");
+    }
+
+    #[test]
+    fn write_diff_line_does_not_synthesize_sigil_for_headers_and_eof_markers() {
+        let mut buf = Vec::new();
+        write_diff_line(&mut buf, 'F', b"diff --git a/x b/x\n");
+        assert_eq!(buf, b"diff --git a/x b/x\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, '=', b"\\ No newline at end of file\n");
+        assert_eq!(buf, b"\\ No newline at end of file\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, 'H', b"@@ -1,3 +1,4 @@\n");
+        assert_eq!(buf, b"@@ -1,3 +1,4 @@\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, '>', b"old filename\n");
+        assert_eq!(buf, b"old filename\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, '<', b"new filename\n");
+        assert_eq!(buf, b"new filename\n");
+
+        buf.clear();
+        write_diff_line(&mut buf, 'B', b"Binary files a/x and b/x differ\n");
+        assert_eq!(buf, b"Binary files a/x and b/x differ\n");
+    }
 }