fix(log): avoid panic when showing log of a branch with no commits

src/screen/mod.rs

@@ -234,6 +234,14 @@ impl Screen {
     }
 
     fn update_cursor(&mut self, nav_mode: NavMode) {
+        // Nothing is selectable (e.g. the log of a branch with no commits).
+        // Reset the cursor to a valid sentinel rather than positioning it,
+        // which would index into an empty `line_index` and panic (#262).
+        if self.line_index.is_empty() {
+            self.cursor = 0;
+            return;
+        }
+
         self.clamp_cursor();
         if self.is_cursor_off_screen() {
             self.move_cursor_to_screen_center();

src/tests/log.rs

@@ -76,3 +76,18 @@ fn log_other_input() {
 fn log_other_invalid() {
     snapshot!(setup(setup_clone!()), "lo <enter>");
 }
+
+#[test]
+fn log_empty_branch() {
+    // Regression for #262: showing the log of a branch with no commits used to
+    // panic ("index out of bounds") because the log screen had no items but the
+    // cursor still indexed into it.
+    let mut ctx = setup_clone!();
+    run(&ctx.dir, &["rm", "-rf", ".git"]);
+    run(&ctx.dir, &["rm", "initial-file"]);
+    run(&ctx.dir, &["git", "init", "--initial-branch=main"]);
+
+    let mut app = ctx.init_app();
+    ctx.update(&mut app, keys("ll"));
+    insta::assert_snapshot!(ctx.redact_buffer());
+}

src/tests/snapshots/gitu__tests__log__log_empty_branch.snap

@@ -0,0 +1,25 @@
+---
+source: src/tests/log.rs
+expression: ctx.redact_buffer()
+---
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+styles_hash: 355101d0bd329837