Add a disconnected highway validation

(closes #3786)

data/core.yaml

@@ -459,6 +459,8 @@ en:
     on_wiki: "{tag} on wiki.osm.org"
     used_with: "used with {type}"
   validations:
+    disconnected_highway: Disconnected highway
+    disconnected_highway_tooltip: "Highways, such as roads and paths, should be connected to other highways."
     untagged_point: Untagged point
     untagged_line: Untagged line
     untagged_area: Untagged area

dist/locales/en.json

@@ -566,6 +566,8 @@
             "used_with": "used with {type}"
         },
         "validations": {
+            "disconnected_highway": "Disconnected highway",
+            "disconnected_highway_tooltip": "Highways, such as roads and paths, should be connected to other highways.",
             "untagged_point": "Untagged point",
             "untagged_line": "Untagged line",
             "untagged_area": "Untagged area",

modules/validations/disconnected_highway.js

@@ -0,0 +1,42 @@
+import { t } from '../util/locale';
+
+
+export function validationDisconnectedHighway() {
+
+
+    function isDisconnectedHighway(entity, graph) {
+        if (!entity.tags.highway) return false;
+        if (entity.geometry(graph) !== 'line') return false;
+
+        return graph.childNodes(entity)
+            .every(function(vertex) {
+                return graph.parentWays(vertex)
+                    .filter(function(parent) {
+                        return parent.tags.highway && parent !== entity;
+                    })
+                    .length === 0;
+            });
+    }
+
+
+    var validation = function(changes, graph) {
+        var warnings = [];
+        for (var i = 0; i < changes.created.length; i++) {
+            var entity = changes.created[i];
+
+            if (isDisconnectedHighway(entity, graph)) {
+                warnings.push({
+                    id: 'missing_tag',
+                    message: t('validations.disconnected_highway'),
+                    tooltip: t('validations.disconnected_highway_tooltip'),
+                    entity: entity
+                });
+            }
+        }
+
+        return warnings;
+    };
+
+
+    return validation;
+}

modules/validations/index.js

@@ -1,4 +1,5 @@
 export { validationDeprecatedTag } from './deprecated_tag';
+export { validationDisconnectedHighway } from './disconnected_highway';
 export { validationManyDeletions } from './many_deletions';
 export { validationMissingTag } from './missing_tag';
 export { validationTagSuggestsArea } from './tag_suggests_area';