implementing a simple graph hash to correct for a buggy hash / == inconsistency (#485)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Stefan Krastanov <github.acc@krastanov.org>

Author: 3 people

Project.toml

@@ -1,6 +1,6 @@
 name = "Graphs"
 uuid = "86223c79-3864-5bf0-83f7-82e725a168b6"
-version = "1.13.3"
+version = "1.13.4"
 
 [deps]
 ArnoldiMethod = "ec485272-7323-5ecc-a04f-4719b315124d"

src/SimpleGraphs/simpledigraph.jl

@@ -435,6 +435,15 @@ function ==(g::SimpleDiGraph, h::SimpleDiGraph)
            badj(g) == badj(h)
 end
 
+function Base.hash(g::SimpleDiGraph, h::UInt)
+    r = hash(typeof(g), h)
+    r = hash(nv(g), r)
+    r = hash(ne(g), r)
+    r = hash(fadj(g), r)
+    r = hash(badj(g), r)
+    return r
+end
+
 is_directed(::Type{<:SimpleDiGraph}) = true
 
 function has_edge(g::SimpleDiGraph{T}, s, d) where {T}

src/SimpleGraphs/simplegraph.jl

@@ -430,6 +430,14 @@ function ==(g::SimpleGraph, h::SimpleGraph)
     return vertices(g) == vertices(h) && ne(g) == ne(h) && fadj(g) == fadj(h)
 end
 
+function Base.hash(g::SimpleGraph, h::UInt)
+    r = hash(typeof(g), h)
+    r = hash(nv(g), r)
+    r = hash(ne(g), r)
+    r = hash(fadj(g), r)
+    return r
+end
+
 """
     is_directed(g)
 

test/simplegraphs/simplegraphs.jl

@@ -103,6 +103,7 @@ using Graphs.Test
 
         @test @inferred(edgetype(g)) == SimpleGraphEdge{T}
         @test @inferred(copy(g)) == g
+        @test @inferred(hash(g)) == hash(copy(g)) == hash(deepcopy(g))
         @test @inferred(!is_directed(g))
 
         e = first(edges(g))
@@ -124,6 +125,8 @@ using Graphs.Test
         @test @inferred(!has_edge(g, 20, 3))
         @test @inferred(!has_edge(g, 2, 30))
 
+        @test @inferred(copy(g)) == g
+        @test @inferred(hash(copy(g))) == hash(g)
         gc = copy(g)
         @test @inferred(add_edge!(gc, 4 => 1)) && gc == cycle_digraph(4)
         @test @inferred(has_edge(gc, 4 => 1)) && has_edge(gc, 0x04 => 0x01)