UI: Insert Function lets Tab reach the category list

The search box asked for the keyboard focus every frame, so Tab moved to the
category list for one frame and the focus went back to the search box. The
dialog now gives the search box the focus once, when it opens, through the
module's take_first_focus, as the other dialogs do.

Test: insert_function_lets_tab_reach_the_category_list (the search box has
the focus and takes typing; after Tab the category list keeps it over several
frames; Space opens the list).

crates/ui-egui/src/dialogs.rs

@@ -856,7 +856,9 @@ impl Dialog {
             "insertFunction" => {
                 // A Function Library menu opens it on its own category.
                 let category = p("category").as_str().unwrap_or(crate::function_library::MOST_RECENTLY_USED).to_string();
-                Dialog::custom("insertFunction", "Insert Function", json!({"category": category}))
+                let mut d = Dialog::custom("insertFunction", "Insert Function", json!({"category": category}));
+                d.focus_first_field = true;
+                d
             }
             "find" => {
                 let mut d = Dialog::custom("find", "Find and Replace", json!({"what": "", "with": "", "within": "sheet", "lookIn": "formulas"}));

crates/ui-egui/src/dialogs/insert_function.rs

@@ -1,4 +1,4 @@
-use super::show::ok_cancel;
+use super::show::{ok_cancel, take_first_focus};
 use super::{Dialog, Json, SheetApp, json, vec2};
 
 /// Insert Function: search names (as the formula language spells them) and descriptions, or pick
@@ -10,7 +10,8 @@ pub(super) fn insert_function(app: &mut SheetApp, ui: &mut egui::Ui, d: &mut Dia
     ui.horizontal(|ui| {
         ui.label(language.tr("Search:"));
         let r = ui.add(egui::TextEdit::singleline(&mut d.search).desired_width(300.0).hint_text(language.tr("e.g. lookup, average, date")));
-        r.request_focus();
+        // Once only, so Tab can move on to the category list.
+        take_first_focus(d, &r);
     });
     // A new search (typed, or set through the control channel) looks through every function, as
     // Excel's does.

crates/ui-egui/src/dialogs/show.rs

@@ -464,7 +464,7 @@ fn form(ui: &mut egui::Ui, d: &mut Dialog, confirm: &mut bool, open: &mut bool)
 /// Enter sets the width, as in Excel.
 /// Keeps asking until the field really has focus: a new window's first frame is an invisible
 /// sizing pass where a focus request is ignored.
-fn take_first_focus(d: &mut Dialog, r: &egui::Response) {
+pub(super) fn take_first_focus(d: &mut Dialog, r: &egui::Response) {
     if !d.focus_first_field {
         return;
     }

crates/ui-egui/tests/it/function_library.rs

@@ -239,6 +239,30 @@ fn insert_function_has_its_title_and_a_working_category_list() {
     assert_ne!(h.state().session.prefs.recent_functions[0], "XLOOKUP");
 }
 
+#[test]
+fn insert_function_lets_tab_reach_the_category_list() {
+    use egui::accesskit::Role;
+    let mut h = formulas_tab(1440.0);
+    click(&mut h, "Insert Function");
+    h.run_steps(3);
+    let search_focused = |h: &Harness| h.get_all_by_role(Role::TextInput).any(|n| n.is_focused());
+    assert!(search_focused(&h), "the search box takes the focus when the dialog opens");
+    h.input_mut().events.push(Event::Text("npv".into()));
+    h.run_steps(2);
+    assert_eq!(h.state().dialog.as_ref().map(|d| d.search.as_str()), Some("npv"));
+    // Tab moves on to the category list, and the search box does not take the focus back.
+    h.input_mut().events.extend([key_event(Key::Tab, true), key_event(Key::Tab, false)]);
+    h.run_steps(5);
+    assert!(h.get_by_role(Role::ComboBox).is_focused(), "Tab reaches the category list");
+    assert!(!search_focused(&h));
+    // The list opens from the keyboard (its Date & Time joins the ribbon's).
+    let listed = |h: &Harness| h.get_all_by_label("Date & Time").count();
+    let before = listed(&h);
+    h.input_mut().events.extend([key_event(Key::Space, true), key_event(Key::Space, false)]);
+    h.run_steps(3);
+    assert_eq!(listed(&h), before + 1, "the list is open");
+}
+
 /// The text shapes the last frame painted, with their left edge and width.
 fn painted_text(h: &Harness) -> Vec<(String, f32, f32)> {
     let mut out = Vec::new();