Merge pull request #164 from JuliaArrays/ismutablejulia1.7

Fix ismutable for Julia 1.7

Author: chriselrod

src/ArrayInterface.jl

@@ -136,11 +136,15 @@ ismutable(::Type{<:Base.ImmutableDict}) = false
 ismutable(::Type{BigFloat}) = false
 ismutable(::Type{BigInt}) = false
 function ismutable(::Type{T}) where {T}
-    if parent_type(T) <: T
-        return T.mutable
+  if parent_type(T) <: T
+    if VERSION ≥ v"1.7.0-DEV.1208"
+      return Base.ismutabletype(T)
     else
-        return ismutable(parent_type(T))
+      return T.mutable
     end
+  else
+    return ismutable(parent_type(T))
+  end
 end
 
 # Piracy