Completed subtrait method.

Author: evetion

src/defaults.jl

@@ -102,15 +102,15 @@ end
 """
     subtrait(t::AbstractGeometryTrait)
 
-Gets the expected (sub)trait for subgeometries (retrieved with [`getgeom`](@ref)) of trait `t`.
+Gets the expected, possible abstract, (sub)trait for subgeometries (retrieved with [`getgeom`](@ref)) of trait `t`.
 This follows the [Type hierarchy](@ref) of Simple Features.
 
 # Examples
 ```jldoctest; setup = :(using GeoInterface)
 julia> GeoInterface.subtrait(GeoInterface.LineStringTrait())
 GeoInterface.PointTrait
-julia> GeoInterface.subtrait(GeoInterface.MultiPointTrait())
-GeoInterface.PointTrait
+julia> GeoInterface.subtrait(GeoInterface.PolygonTrait())  # Any of LineStringTrait, LineTrait, LinearRingTrait
+GeoInterface.AbstractLineStringTrait
 ```
 ```jldoctest; setup = :(using GeoInterface)
 # `nothing` is returned when there's no subtrait or when it's not known beforehand
@@ -120,10 +120,15 @@ julia> isnothing(GeoInterface.subtrait(GeoInterface.GeometryCollectionTrait()))
 true
 ```
 """
-subtrait(::PointTrait) = nothing
-subtrait(::LineStringTrait) = PointTrait
-subtrait(::PolygonTrait) = LineStringTrait
-subtrait(::MultiPointTrait) = PointTrait
-subtrait(::MultiLineStringTrait) = LineStringTrait
-subtrait(::MultiPolygonTrait) = PolygonTrait
-subtrait(::GeometryCollectionTrait) = nothing
+subtrait(::AbstractPointTrait) = nothing
+subtrait(::AbstractCurveTrait) = AbstractPointTrait
+subtrait(::AbstractCurvePolygonTrait) = AbstractCurveTrait
+subtrait(::AbstractPolygonTrait) = AbstractLineStringTrait
+subtrait(::AbstractPolyHedralSurfaceTrait) = AbstractPolygonTrait
+subtrait(::TINTrait) = TriangleTrait
+subtrait(::AbstractMultiPointTrait) = AbstractPointTrait
+subtrait(::AbstractMultiLineStringTrait) = AbstractLineStringTrait
+subtrait(::AbstractMultiPolygonTrait) = AbstractPolygonTrait
+subtrait(::AbstractMultiSurfaceTrait) = AbstractSurfaceTrait
+subtrait(::AbstractGeometryCollectionTrait) = nothing
+subtrait(::AbstractGeometryTrait) = nothing  # fallback

src/types.jl

@@ -73,6 +73,8 @@ struct MultiLineStringTrait <: AbstractMultiLineStringTrait end
 
 """An AbstractMultiSurfaceTrait type for all multisurfaces."""
 abstract type AbstractMultiSurfaceTrait <: AbstractGeometryCollectionTrait end
+"""A MultiSurfaceTrait is a collection of [`AbstractSurfaceTrait`](@ref)s."""
+struct MultiSurfaceTrait <: AbstractMultiSurfaceTrait end
 """An AbstractMultiPolygonTrait type for all multipolygons."""
 abstract type AbstractMultiPolygonTrait <: AbstractMultiSurfaceTrait end
 """A MultiPolygonTrait is a collection of [`PolygonTrait`](@ref)s."""

src/utils.jl

@@ -13,7 +13,10 @@ function testgeometry(geom)
             n = ngeom(geom)
             if n >= 1  # geometry could be empty
                 g2 = getgeom(geom, 1)
-                geomtype(g2) == subtrait(type)
+                subtype = subtrait(type)
+                if !isnothing(subtype)
+                    @assert geomtype(g2) isa subtype
+                end
                 @assert testgeometry(g2)  # recursive testing of subgeometries
             end
         end

test/test_primitives.jl

@@ -1,9 +1,9 @@
-struct MyCurve end
-struct MyPoint end
+
 
 @testset "Developer" begin
     # Implement interface
-
+    struct MyCurve end
+    struct MyPoint end
     GeoInterface.isgeometry(::MyPoint) = true
     GeoInterface.isgeometry(::MyCurve) = true
     GeoInterface.geomtype(::MyPoint) = GeoInterface.PointTrait()
@@ -26,5 +26,8 @@ struct MyPoint end
     point = GeoInterface.getgeom(geom, 1)
     @test GeoInterface.y(point) == 2
 
+end
 
+@testset "Defaults" begin
+    @test GeoInterface.subtrait(GeoInterface.TINTrait()) == GeoInterface.TriangleTrait
 end