show sidewalks disconnected in edit impact. prerequisite to preventing this.

game/src/edit/impact.rs

@@ -1,5 +1,6 @@
 use crate::ui::UI;
 use abstutil::{prettyprint_usize, Timer};
+use map_model::connectivity;
 use sim::Scenario;
 
 // Edits have been applied.
@@ -23,5 +24,11 @@ pub fn edit_impacts(scenario: Option<Scenario>, ui: &mut UI, timer: &mut Timer)
         lines.push("No scenario, so no trips impacted".to_string());
     }
 
+    let (_, disconnected) = connectivity::find_sidewalk_scc(&ui.primary.map);
+    // TODO Display them
+    if !disconnected.is_empty() {
+        lines.push(format!("{} sidewalks disconnected", disconnected.len()));
+    }
+
     lines
 }

map_model/src/connectivity.rs

@@ -0,0 +1,37 @@
+use crate::{LaneID, Map};
+use petgraph::graphmap::DiGraphMap;
+use std::collections::HashSet;
+
+// SCC = strongly connected component
+
+// TODO Move make/parking_blackholes.rs logic here.
+// TODO Move debug/floodfill.rs logic here.
+
+// Returns (sidewalks in main component, disconnected sidewalks)
+pub fn find_sidewalk_scc(map: &Map) -> (HashSet<LaneID>, HashSet<LaneID>) {
+    let mut graph = DiGraphMap::new();
+    for turn in map.all_turns().values() {
+        if map.is_turn_allowed(turn.id) && turn.between_sidewalks() {
+            graph.add_edge(turn.id.src, turn.id.dst, 1);
+        }
+    }
+    let components = petgraph::algo::kosaraju_scc(&graph);
+    let largest_group: HashSet<LaneID> = components
+        .into_iter()
+        .max_by_key(|c| c.len())
+        .unwrap()
+        .into_iter()
+        .collect();
+    let disconnected = map
+        .all_lanes()
+        .iter()
+        .filter_map(|l| {
+            if l.is_sidewalk() && !largest_group.contains(&l.id) {
+                Some(l.id)
+            } else {
+                None
+            }
+        })
+        .collect();
+    (largest_group, disconnected)
+}

map_model/src/lib.rs

@@ -1,6 +1,7 @@
 mod area;
 mod building;
 mod bus_stop;
+pub mod connectivity;
 mod edits;
 mod intersection;
 mod lane;

map_model/src/map.rs

@@ -1,10 +1,10 @@
 use crate::pathfind::Pathfinder;
 use crate::raw::{OriginalIntersection, OriginalRoad, RawMap};
 use crate::{
-    make, osm, Area, AreaID, Building, BuildingID, BusRoute, BusRouteID, BusStop, BusStopID,
-    ControlStopSign, ControlTrafficSignal, Intersection, IntersectionID, IntersectionType, Lane,
-    LaneID, LaneType, MapEdits, Path, PathRequest, Position, Road, RoadID, Turn, TurnID,
-    TurnPriority, LANE_THICKNESS,
+    connectivity, make, osm, Area, AreaID, Building, BuildingID, BusRoute, BusRouteID, BusStop,
+    BusStopID, ControlStopSign, ControlTrafficSignal, Intersection, IntersectionID,
+    IntersectionType, Lane, LaneID, LaneType, MapEdits, Path, PathRequest, Position, Road, RoadID,
+    Turn, TurnID, TurnPriority, LANE_THICKNESS,
 };
 use abstutil;
 use abstutil::{deserialize_btreemap, serialize_btreemap, Error, Timer};
@@ -178,6 +178,14 @@ impl Map {
         }
         timer.stop("find parking blackholes");
 
+        let (_, disconnected) = connectivity::find_sidewalk_scc(&m);
+        if !disconnected.is_empty() {
+            timer.warn(format!(
+                "{} sidewalks are disconnected!",
+                disconnected.len()
+            ));
+        }
+
         timer.stop("finalize Map");
         m
     }