prevent degenerate ways caused by deleting a corner of a triangle

CHANGELOG.md

@@ -42,12 +42,15 @@ _Breaking developer changes, which may affect downstream projects or sites that
 #### :camera: Street-Level
 #### :white_check_mark: Validation
 #### :bug: Bugfixes
+* Prevent degenerate ways caused by deleting a corner of a triangle ([#10003], thanks [@k-yle])
 #### :earth_asia: Localization
 #### :hourglass: Performance
 #### :mortar_board: Walkthrough / Help
 #### :rocket: Presets
 #### :hammer: Development
 
+[#10003]: https://github.com/openstreetmap/iD/pull/10003
+
 
 # 2.31.0
 ##### 2025-Feb-05

modules/osm/way.js

@@ -242,7 +242,7 @@ Object.assign(osmWay.prototype, {
 
 
     isDegenerate: function() {
-        return (new Set(this.nodes).size < (this.isArea() ? 3 : 2));
+        return (new Set(this.nodes).size < (this.isClosed() ? 3 : 2));
     },
 
 

test/spec/actions/circularize.js

@@ -278,10 +278,11 @@ describe('iD.actionCircularize', function () {
         var graph = iD.coreGraph([
                 iD.osmNode({id: 'a', loc: [0, 0]}),
                 iD.osmNode({id: 'b', loc: [0, 2]}),
-                iD.osmWay({id: '-', nodes: ['a', 'b', 'a']})
+                iD.osmNode({id: 'c', loc: [2, 0]}),
+                iD.osmWay({id: '-', nodes: ['a', 'b', 'c', 'a']})
             ]);
 
-        expect(area('-', graph)).to.eql(0);
+        expect(area('-', graph)).to.eql(2);
 
         graph = iD.actionCircularize('-', projection)(graph);
 

test/spec/osm/way.js

@@ -473,6 +473,10 @@ describe('iD.osmWay', function() {
             expect(iD.osmWay({nodes: ['a', 'b']}).isDegenerate()).to.equal(false);
         });
 
+        it('returns true for a linear way that doubles back on itself', function () {
+            expect(iD.osmWay({nodes: ['a', 'b', 'a']}).isDegenerate()).to.equal(true);
+        });
+
         it('returns true for an area with zero, one, or two unique nodes', function () {
             expect(iD.osmWay({tags: {area: 'yes'}, nodes: []}).isDegenerate()).to.equal(true);
             expect(iD.osmWay({tags: {area: 'yes'}, nodes: ['a', 'a']}).isDegenerate()).to.equal(true);