Complete Graphs.jl AbstractGraph API for IGraph

CHANGELOG.md

@@ -1,5 +1,11 @@
 # News
 
+## Unreleased
+
+- Complete `Graphs.jl` `AbstractGraph` interface for `IGraph`: `edges`, `outneighbors`/`inneighbors`, `add_vertex!`, `rem_vertex!`, `copy`.
+- Fix 0-indexing bug in `has_edge` (was passing 1-based indices to 0-based C API).
+- Add `GraphsInterfaceChecker.jl` compliance tests.
+
 ## v1.0.0 - 2025-09-25
 
 - Update the underlying igraph C library to v1.0.0.

src/graph_api.jl

@@ -33,15 +33,63 @@ end
 
 Base.eltype(::IGraph) = LibIGraph.igraph_int_t
 Base.zero(::Type{IGraph}) = IGraph(0)
-# Graphs.edges # TODO
 Graphs.edgetype(g::IGraph) = Graphs.SimpleGraphs.SimpleEdge{eltype(g)} # TODO maybe expose the edge id information from IGraph
-Graphs.has_edge(g::IGraph,s,d) = LibIGraph.get_eid(g,s,d,false,false)[1]!=-1
+Graphs.has_edge(g::IGraph,s,d) = LibIGraph.get_eid(g,s-1,d-1,false,false)[1]!=-1
 Graphs.has_vertex(g::IGraph,n::Integer) = 1≤n≤Graphs.nv(g)
-# Graphs.inneighbors # TODO
 Graphs.is_directed(::Type{IGraph}) = false # TODO support directed graphs
 Graphs.ne(g::IGraph) = LibIGraph.ecount(g)
 Graphs.nv(g::IGraph) = LibIGraph.vcount(g)
-# Graphs.outneighbors # TODO
 Graphs.vertices(g::IGraph) = 1:Graphs.nv(g)
 
-Graphs.add_edge!(g::IGraph, e::Graphs.SimpleGraphEdge) = LibIGraph.add_edge(g,e.src-1,e.dst-1)
+struct IGraphEdgeIterator
+    graph::IGraph
+end
+
+Base.length(it::IGraphEdgeIterator) = Graphs.ne(it.graph)
+Base.eltype(::Type{IGraphEdgeIterator}) = Graphs.SimpleGraphs.SimpleEdge{LibIGraph.igraph_int_t}
+
+function Base.iterate(it::IGraphEdgeIterator, eid=0)
+    eid ≥ Graphs.ne(it.graph) && return nothing
+    (from, to) = LibIGraph.edge(it.graph, eid)
+    return (Graphs.SimpleGraphs.SimpleEdge(from+1, to+1), eid+1)
+end
+
+Graphs.edges(g::IGraph) = IGraphEdgeIterator(g)
+
+function Graphs.outneighbors(g::IGraph, v::Integer)
+    neis = IGVectorInt()
+    LibIGraph.neighbors(g, neis, v-1, LibIGraph.IGRAPH_ALL, LibIGraph.IGRAPH_NO_LOOPS, LibIGraph.IGRAPH_NO_MULTIPLE)
+    result = Vector{LibIGraph.igraph_int_t}(undef, length(neis))
+    for i in eachindex(result)
+        result[i] = neis[i] + 1
+    end
+    return sort!(result)
+end
+
+Graphs.inneighbors(g::IGraph, v::Integer) = Graphs.outneighbors(g, v)
+
+function Graphs.add_edge!(g::IGraph, s::Integer, d::Integer)
+    s == d && return false  # no self-loops for simple graphs
+    Graphs.has_edge(g, s, d) && return false
+    LibIGraph.add_edge(g, s-1, d-1)
+    return true
+end
+Graphs.add_edge!(g::IGraph, e::Graphs.SimpleGraphEdge) = Graphs.add_edge!(g, e.src, e.dst)
+
+function Graphs.add_vertex!(g::IGraph)
+    LibIGraph.igraph_add_vertices(g.objref, LibIGraph.igraph_int_t(1), C_NULL)
+    return true
+end
+
+function Graphs.rem_vertex!(g::IGraph, v::Integer)
+    Graphs.has_vertex(g, v) || return false
+    vs = LibIGraph.igraph_vss_1(LibIGraph.igraph_int_t(v-1))
+    LibIGraph.igraph_delete_vertices(g.objref, vs)
+    return true
+end
+
+function Base.copy(g::IGraph)
+    g2 = IGraph(;_uninitialized=Val(true))
+    LibIGraph.copy(g2, g)
+    return g2
+end

test/Project.toml

@@ -5,6 +5,7 @@ DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
 Graphs = "86223c79-3864-5bf0-83f7-82e725a168b6"
+GraphsInterfaceChecker = "3bef136c-15ff-4091-acbb-1a4aafe67608"
 IGraphs = "647e90d3-2106-487c-adb4-c91fc07b96ea"
 Interfaces = "85a1e053-f937-4924-92a5-1367d23b7b87"
 JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"

test/test_graphs_interface.jl

@@ -0,0 +1,77 @@
+@testitem "GraphsInterfaceChecker" begin
+
+using IGraphs
+using Graphs
+using GraphsInterfaceChecker
+using Interfaces
+using Test
+
+# Build a few representative graphs for testing
+graphs = IGraph[
+    IGraph(cycle_graph(5)),
+    IGraph(path_graph(4)),
+    IGraph(complete_graph(6)),
+    IGraph(star_graph(5)),
+]
+
+# Test the mandatory part of the AbstractGraph interface
+@test Interfaces.test(AbstractGraphInterface, IGraph, graphs; show=false)
+
+# Test the optional mutation interface
+@test Interfaces.test(AbstractGraphInterface{(:mutation,)}, IGraph, graphs; show=false)
+
+@testset "edges roundtrip" begin
+    for g in graphs
+        sg = SimpleGraph(g)
+        ig = IGraph(sg)
+        @test Set(collect(edges(ig))) == Set(collect(edges(sg)))
+        @test nv(ig) == nv(sg)
+        @test ne(ig) == ne(sg)
+    end
+end
+
+@testset "neighbors" begin
+    g = IGraph(cycle_graph(5))
+    @test sort(outneighbors(g, 1)) == [2, 5]
+    @test sort(outneighbors(g, 3)) == [2, 4]
+    @test inneighbors(g, 1) == outneighbors(g, 1)
+end
+
+@testset "has_edge" begin
+    g = IGraph(path_graph(4))
+    @test has_edge(g, 1, 2)
+    @test has_edge(g, 2, 1)
+    @test has_edge(g, 2, 3)
+    @test !has_edge(g, 1, 3)
+    @test !has_edge(g, 1, 4)
+end
+
+@testset "mutation" begin
+    g = IGraph(path_graph(3))
+    @test nv(g) == 3
+    @test ne(g) == 2
+
+    @test add_vertex!(g)
+    @test nv(g) == 4
+    @test add_edge!(g, 3, 4)
+    @test ne(g) == 3
+    @test has_edge(g, 3, 4)
+
+    # Duplicate edge
+    @test !add_edge!(g, 3, 4)
+    # Self-loop
+    @test !add_edge!(g, 1, 1)
+
+    g2 = copy(g)
+    @test nv(g2) == nv(g)
+    @test ne(g2) == ne(g)
+    add_vertex!(g2)
+    @test nv(g2) == nv(g) + 1
+
+    @test rem_vertex!(g, 4)
+    @test nv(g) == 3
+    @test ne(g) == 2
+    @test !rem_vertex!(g, 10)
+end
+
+end