Popup a message when the auto-filter has no effect

apps/ltn/src/browse.rs

@@ -165,7 +165,8 @@ impl State<App> for BrowseNeighborhoods {
                         {
                             timer.next();
                             let neighborhood = Neighborhood::new(ctx, app, id);
-                            app.session.heuristic.apply(ctx, app, &neighborhood, timer);
+                            // Ignore errors
+                            let _ = app.session.heuristic.apply(ctx, app, &neighborhood, timer);
                         }
                     });
                     return Transition::Replace(BrowseNeighborhoods::new_state(ctx, app));

apps/ltn/src/connectivity.rs

@@ -4,7 +4,7 @@ use geom::{Angle, ArrowCap, Distance, PolyLine};
 use map_gui::tools::ColorNetwork;
 use map_model::{IntersectionID, Perimeter};
 use widgetry::mapspace::{ToggleZoomed, World};
-use widgetry::tools::PolyLineLasso;
+use widgetry::tools::{PolyLineLasso, PopupMsg};
 use widgetry::{
     DrawBaselayer, EventCtx, GfxCtx, Key, Line, Outcome, Panel, ScreenPt, State, Text, TextExt,
     Toggle, Widget,
@@ -115,14 +115,24 @@ impl State<App> for Viewer {
         match self.left_panel.event(ctx) {
             Outcome::Clicked(x) => {
                 if x == "Automatically stop rat-runs" {
-                    ctx.loading_screen("automatically filter a neighborhood", |ctx, timer| {
+                    match ctx.loading_screen("automatically filter a neighborhood", |ctx, timer| {
                         app.session
                             .heuristic
-                            .apply(ctx, app, &self.neighborhood, timer);
-                    });
-                    self.neighborhood = Neighborhood::new(ctx, app, self.neighborhood.id);
-                    self.update(ctx, app);
-                    return Transition::Keep;
+                            .apply(ctx, app, &self.neighborhood, timer)
+                    }) {
+                        Ok(()) => {
+                            self.neighborhood = Neighborhood::new(ctx, app, self.neighborhood.id);
+                            self.update(ctx, app);
+                            return Transition::Keep;
+                        }
+                        Err(err) => {
+                            return Transition::Push(PopupMsg::new_state(
+                                ctx,
+                                "Error",
+                                vec![err.to_string()],
+                            ));
+                        }
+                    }
                 } else if x == "Create filters along a shape" {
                     return Transition::Push(FreehandFilters::new_state(
                         ctx,

apps/ltn/src/filters/auto.rs

@@ -1,5 +1,7 @@
 //! Experiments to make a neighborhood be low-traffic by automatically placing filters to prevent all rat runs.
 
+use anyhow::Result;
+
 use abstutil::Timer;
 use map_model::RoadID;
 use widgetry::{Choice, EventCtx};
@@ -41,7 +43,7 @@ impl Heuristic {
         app: &mut App,
         neighborhood: &Neighborhood,
         timer: &mut Timer,
-    ) {
+    ) -> Result<()> {
         if neighborhood
             .cells
             .iter()
@@ -49,10 +51,7 @@ impl Heuristic {
             .count()
             != 0
         {
-            warn!(
-                "Not automatically changing this neighborhood; it already has a disconnected cell"
-            );
-            return;
+            bail!("This neighborhood has a disconnected cell; fix that first");
         }
 
         // TODO If we already have no rat-runs, stop
@@ -66,8 +65,13 @@ impl Heuristic {
             Heuristic::OnlyOneBorder => only_one_border(app, neighborhood),
         }
 
-        app.session.modal_filters.cancel_empty_edit();
+        let empty = app.session.modal_filters.cancel_empty_edit();
         after_edit(ctx, app);
+        if empty {
+            bail!("No new filters created");
+        } else {
+            Ok(())
+        }
     }
 }
 

apps/ltn/src/filters/mod.rs

@@ -57,16 +57,18 @@ impl ModalFilters {
     }
 
     /// If it's possible no edits were made, undo the previous call to `before_edit` and collapse
-    /// the redundant piece of history.
-    pub fn cancel_empty_edit(&mut self) {
+    /// the redundant piece of history. Returns true if the edit was indeed empty.
+    pub fn cancel_empty_edit(&mut self) -> bool {
         if let Some(prev) = self.previous_version.take() {
             if self.roads == prev.roads && self.intersections == prev.intersections {
                 self.previous_version = prev.previous_version;
+                return true;
             } else {
                 // There was a real difference, keep
                 self.previous_version = Box::new(Some(prev));
             }
         }
+        false
     }
 
     /// Modify RoutingParams to respect these modal filters