move shuffling of animals to be done on demand instead of during initialization

Author: KristofferC

src/MacroTools.jl

@@ -23,8 +23,5 @@ _animals = split(read(animals_file, String))
 resize!(animals, length(_animals))
 animals .= Symbol.(lowercase.(_animals))
 
-function __init__()
-    Random.shuffle!(animals)
-end
 
 end # module

src/utils.jl

@@ -190,6 +190,9 @@ function gensym_ids(ex)
   end
 end
 
+const l = ReentrantLock()
+const shuffled = Ref{Bool}(false)
+
 """
     alias_gensyms(expr)
 
@@ -205,6 +208,12 @@ julia> MacroTools.alias_gensyms(:(\$x+\$y))
 ```
 """
 function alias_gensyms(ex)
+  lock(l) do
+    if !shuffled[]
+      Random.shuffle!(animals)
+      shuffled[] = true
+    end
+  end
   left = copy(animals)
   syms = Dict{Symbol, Symbol}()
   prewalk(ex) do x