fix(gh): skip compact_diff for --name-only/--stat flags in pr diff

When `gh pr diff` is called with output-format-changing flags like
--name-only, --stat, --name-status, --numstat, or --shortstat, the
output is a plain filename/stat list rather than a unified diff.
compact_diff() expects diff headers and hunks, so it produces empty
output from these formats.

Skip filtering and passthrough directly when any of these flags are
present. The output is already compact and doesn't benefit from diff
compaction.

Fixes #730

Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

Author: mvanhorn

src/gh_cmd.rs

@@ -1118,6 +1118,18 @@ fn pr_merge(args: &[String], _verbose: u8) -> Result<()> {
     Ok(())
 }
 
+/// Flags that change `gh pr diff` output from unified diff to a different format.
+/// When present, compact_diff would produce empty output since it expects diff headers.
+fn has_non_diff_format_flag(args: &[String]) -> bool {
+    args.iter().any(|a| {
+        a == "--name-only"
+            || a == "--name-status"
+            || a == "--stat"
+            || a == "--numstat"
+            || a == "--shortstat"
+    })
+}
+
 fn pr_diff(args: &[String], _verbose: u8) -> Result<()> {
     // --no-compact: pass full diff through (gh CLI doesn't know this flag, strip it)
     let no_compact = args.iter().any(|a| a == "--no-compact");
@@ -1127,7 +1139,9 @@ fn pr_diff(args: &[String], _verbose: u8) -> Result<()> {
         .cloned()
         .collect();
 
-    if no_compact {
+    // Passthrough when --no-compact or when a format flag changes output away from
+    // unified diff (e.g. --name-only produces a filename list, not diff hunks).
+    if no_compact || has_non_diff_format_flag(&gh_args) {
         return run_passthrough_with_extra("gh", &["pr", "diff"], &gh_args);
     }
 
@@ -1538,6 +1552,46 @@ mod tests {
         assert!(!should_passthrough_issue_view(&[]));
     }
 
+    // --- has_non_diff_format_flag tests ---
+
+    #[test]
+    fn test_non_diff_format_flag_name_only() {
+        assert!(has_non_diff_format_flag(&["--name-only".into()]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_stat() {
+        assert!(has_non_diff_format_flag(&["--stat".into()]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_name_status() {
+        assert!(has_non_diff_format_flag(&["--name-status".into()]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_numstat() {
+        assert!(has_non_diff_format_flag(&["--numstat".into()]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_shortstat() {
+        assert!(has_non_diff_format_flag(&["--shortstat".into()]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_absent() {
+        assert!(!has_non_diff_format_flag(&[]));
+    }
+
+    #[test]
+    fn test_non_diff_format_flag_regular_args() {
+        assert!(!has_non_diff_format_flag(&[
+            "123".into(),
+            "--color=always".into()
+        ]));
+    }
+
     // --- filter_markdown_body tests ---
 
     #[test]