Deprecate storing 0 in IntSets

This paves the way towards better IndexSet semantics.

base/intset.jl

@@ -55,8 +55,12 @@ function push!(s::IntSet, n::Integer)
             lim = Int(n + div(n,2))
             sizehint!(s, lim)
         end
-    elseif n < 0
-        throw(ArgumentError("IntSet elements cannot be negative"))
+    elseif n <= 0
+        if n < 0
+            throw(ArgumentError("IntSet elements cannot be negative"))
+        else
+            depwarn("storing zero in IntSets is deprecated", :push!)
+        end
     end
     s.bits[n>>5 + 1] |= (UInt32(1)<<(n&31))
     return s
@@ -78,8 +82,12 @@ function pop!(s::IntSet, n::Integer, deflt)
             return deflt
         end
     end
-    if n < 0
-        return deflt
+    if n <= 0
+        if n < 0
+            return deflt
+        else
+            depwarn("stored zeros in IntSet is deprecated", :pop!)
+        end
     end
     mask = UInt32(1)<<(n&31)
     idx = n>>5 + 1
@@ -147,12 +155,15 @@ function in(n::Integer, s::IntSet)
     if n >= s.limit
         # max IntSet length is typemax(Int), so highest possible element is
         # typemax(Int)-1
-        s.fill1s && n >= 0 && n < typemax(Int)
-    elseif n < 0
-        return false
-    else
-        (s.bits[n>>5 + 1] & (UInt32(1)<<(n&31))) != 0
+        return s.fill1s && n >= 0 && n < typemax(Int)
+    elseif n <= 0
+        if n < 0
+            return false
+        else
+            depwarn("stored zeros in IntSet is deprecated", :in)
+        end
     end
+    (s.bits[n>>5 + 1] & (UInt32(1)<<(n&31))) != 0
 end
 
 start(s::IntSet) = Int64(0)

test/intset.jl

@@ -21,16 +21,16 @@ data_out = collect(s)
 @test sprint(show, IntSet([1,2,3])) == "IntSet([1, 2, 3])"
 
 
-s = IntSet([0,1,10,20,200,300,1000,10000,10002])
+s = IntSet([1,2,10,20,200,300,1000,10000,10002])
 @test last(s) == 10002
-@test first(s) == 0
+@test first(s) == 1
 @test length(s) == 9
 @test pop!(s) == 10002
 @test_throws KeyError pop!(s, -1)
 @test length(s) == 8
-@test shift!(s) == 0
+@test shift!(s) == 1
 @test length(s) == 7
-@test !in(0,s)
+@test !in(1,s)
 @test !in(10002,s)
 @test in(10000,s)
 @test_throws ArgumentError first(IntSet())
@@ -53,7 +53,7 @@ s = IntSet(255)
 
 # issue #7851
 @test_throws ArgumentError IntSet(-1)
-@test !(-1 in IntSet(0:10))
+@test !(-1 in IntSet(1:10))
 
 # # issue #8570
 # This requires 2^29 bytes of storage, which is too much for a simple test