Reject invalid Git comparisons before launching the TUI

src/cli.rs

@@ -178,9 +178,9 @@ pub(crate) fn run(runtime: &tokio::runtime::Runtime) -> Result<i32> {
         }
         None => {}
     }
-    let streaming = args.format.is_some();
     let metadata_or_quiet = args.quiet || args.metadata();
-    if !streaming && !metadata_or_quiet {
+    let interactive = args.format.is_none() && !metadata_or_quiet;
+    if interactive && args.no_index {
         return launch_tui(&frontend_args, true);
     }
     if args.no_index {
@@ -194,6 +194,11 @@ pub(crate) fn run(runtime: &tokio::runtime::Runtime) -> Result<i32> {
     let repo = gix::discover(&location)?;
     let workspace = repo.workdir().unwrap_or(repo.git_dir());
     let (comparison, paths) = select(&repo, &location, &args, has_separator)?;
+    if interactive {
+        // Reject invalid revisions before the UI takes over the terminal.
+        comparison.resolve(&repo)?;
+        return launch_tui(&frontend_args, true);
+    }
     let files = FileParams {
         paths,
         // `-M` conflicts with `--no-renames`; renames are on by default.

tests/git_comparison.rs

@@ -42,6 +42,27 @@ fn statuses(text: &str) -> Vec<String> {
         .collect()
 }
 
+#[test]
+fn invalid_revision_range_is_rejected_before_the_terminal_ui() {
+    let dir = tempfile::tempdir().unwrap();
+    let repo = gix::init(dir.path()).unwrap();
+    commit(&repo, "base");
+    commit(&repo, "head");
+
+    let output = diffr(dir.path(), &["HEAD^2..HEAD"]);
+    assert_eq!(output.status.code(), Some(2));
+    assert!(output.stdout.is_empty());
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    assert!(
+        stderr.contains("unknown revision or path \"HEAD^2..HEAD\""),
+        "{stderr}"
+    );
+
+    let output = diffr(dir.path(), &["HEAD^..HEAD"]);
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    assert!(stderr.contains("terminal UI needs a terminal"), "{stderr}");
+}
+
 #[test]
 fn revisions_index_worktree_reverse_paths_and_stats_match_git() {
     let dir = tempfile::tempdir().unwrap();