Fix for empty geometries. (#209)

* Fix for empty geometries.

* Add test for empty polygon geometry

Tests that npoint and nring return 0 for empty polygons,
verifying the init=0 fix works correctly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

* Remove typehint.

---------

Co-authored-by: Anshul Singhvi <[email protected]>
Co-authored-by: Claude Opus 4.5 <[email protected]>

Author: 3 people

src/fallbacks.jl

@@ -43,7 +43,7 @@ getexterior(t::AbstractPolygonTrait, geom) = getring(t, geom, 1)
 nhole(t::AbstractPolygonTrait, geom) = nring(t, geom) - 1
 gethole(t::AbstractPolygonTrait, geom) = (getgeom(t, geom, i) for i in 2:ngeom(t, geom))
 gethole(t::AbstractPolygonTrait, geom, i) = getring(t, geom, i + 1)
-npoint(t::AbstractPolygonTrait, geom) = sum(npoint(p) for p in getring(t, geom))
+npoint(t::AbstractPolygonTrait, geom) = sum(npoint(p) for p in getring(t, geom); init=0)
 getpoint(t::AbstractPolygonTrait, geom) = flatten((p for p in getpoint(r)) for r in getring(t, geom))
 
 ## MultiPoint
@@ -55,16 +55,16 @@ getpoint(t::AbstractMultiPointTrait, geom, i) = getgeom(t, geom, i)
 nlinestring(t::AbstractMultiCurveTrait, geom) = ngeom(t, geom)
 getlinestring(t::AbstractMultiCurveTrait, geom) = getgeom(t, geom)
 getlinestring(t::AbstractMultiCurveTrait, geom, i) = getgeom(t, geom, i)
-npoint(t::AbstractMultiCurveTrait, geom) = sum(npoint(ls) for ls in getgeom(t, geom))
+npoint(t::AbstractMultiCurveTrait, geom) = sum(npoint(ls) for ls in getgeom(t, geom); init=0)
 getpoint(t::AbstractMultiCurveTrait, geom) = flatten((p for p in getpoint(ls)) for ls in getgeom(t, geom))
 
 ## MultiPolygon
 npolygon(t::AbstractMultiPolygonTrait, geom) = ngeom(t, geom)
 getpolygon(t::AbstractMultiPolygonTrait, geom) = getgeom(t, geom)
 getpolygon(t::AbstractMultiPolygonTrait, geom, i) = getgeom(t, geom, i)
-nring(t::AbstractMultiPolygonTrait, geom) = sum(nring(p) for p in getpolygon(t, geom))
+nring(t::AbstractMultiPolygonTrait, geom) = sum(nring(p) for p in getpolygon(t, geom); init=0)
 getring(t::AbstractMultiPolygonTrait, geom) = flatten((r for r in getring(p)) for p in getpolygon(t, geom))
-npoint(t::AbstractMultiPolygonTrait, geom) = sum(npoint(r) for r in getring(t, geom))
+npoint(t::AbstractMultiPolygonTrait, geom) = sum(npoint(r) for r in getring(t, geom); init=0)
 getpoint(t::AbstractMultiPolygonTrait, geom) = flatten((p for p in getpoint(r)) for r in getring(t, geom))
 
 ## Surface
@@ -130,6 +130,7 @@ function calc_extent(t::AbstractPointTrait, geom)
     end
 end
 function calc_extent(t::AbstractGeometryTrait, geom)
+    isempty(t, geom) && return nothing
     points = getpoint(t, geom)
     X = extrema(p -> x(p), points)
     Y = extrema(p -> y(p), points)

test/test_primitives.jl

@@ -8,6 +8,7 @@ struct MyPoint end
 struct MyEmptyPoint end
 struct MyCurve end
 struct MyPolygon end
+struct MyEmptyPolygon end
 struct MyTriangle end
 struct MyMultiPoint end
 struct MyMultiCurve end
@@ -46,6 +47,12 @@ GeoInterface.ngeom(::PolygonTrait, geom::MyPolygon) = 2
 GeoInterface.getgeom(::PolygonTrait, geom::MyPolygon, i) = MyCurve()
 GeoInterface.ncoord(t::PolygonTrait, geom::MyPolygon) = 2
 
+GeoInterface.isgeometry(::Type{MyEmptyPolygon}) = true
+GeoInterface.geomtrait(::MyEmptyPolygon) = PolygonTrait()
+GeoInterface.ngeom(::PolygonTrait, geom::MyEmptyPolygon) = 0
+GeoInterface.getgeom(::PolygonTrait, geom::MyEmptyPolygon, i) = nothing
+GeoInterface.isempty(::PolygonTrait, geom::MyEmptyPolygon) = true
+
 GeoInterface.isgeometry(::Type{MyTriangle}) = true
 GeoInterface.geomtrait(::MyTriangle) = TriangleTrait()
 GeoInterface.ngeom(::TriangleTrait, geom::MyTriangle) = 3
@@ -173,6 +180,11 @@ GeoInterface.crs(::RasterTrait, ::Raster) = GeoFormatTypes.EPSG(4326)
         @test GeoInterface.nring(geom) == 1
         @test GeoInterface.nhole(geom) == 0
         @test GeoInterface.npoint(geom) == 3
+
+        geom = MyEmptyPolygon()
+        @test GeoInterface.isempty(geom)
+        @test GeoInterface.nring(geom) == 0
+        @test GeoInterface.npoint(geom) == 0
     end
 
     @testset "MultiPoint" begin