Simplify hash of VariableTimeZone (JuliaTime#281)

Co-authored-by: Eric Davies <iamed2@gmail.com>
Co-authored-by: Curtis Vogt <curtis.vogt@gmail.com>

Author: 3 people

src/types/variabletimezone.jl

@@ -39,8 +39,7 @@ function Base.isequal(a::VariableTimeZone, b::VariableTimeZone)
 end
 
 function Base.hash(tz::VariableTimeZone, h::UInt)
+    h = hash(:timezone, h)
     h = hash(tz.name, h)
-    h = hash(tz.transitions, h)
-    h = hash(tz.cutoff, h)
     return h
 end

test/types/variabletimezone.jl

@@ -44,6 +44,18 @@
         @test a == b
         @test a !== b
         @test !isequal(a, b)
-        @test hash(a) != hash(b)
+        @test hash(a) == hash(b)
+    end
+    
+    @testset "hash using name" begin
+        a = first(compile("Europe/Warsaw", tzdata["europe"]))
+        b = VariableTimeZone("Europe/Warsaw", a.transitions[1:1], nothing)
+
+        # To be fast the `hash` function only uses the name. However, when a hash collision
+        # does occur it should be disambiguated by the `isequal` check which also considers
+        # the transition and the cutoff.
+        @test hash(a) == hash(b)
+        @test !isequal(a, b)
+        @test length(keys(Dict(a => :a, b => :b))) == 2  # Time zones use different keys
     end
 end