Adjust to upcoming julia#54341 (#125)

The feature check is done using julia#53849 (which is itself a bit of an experiment),
so the idea is to merge/tag this before the base PR is merged to prevent breakage on julia master.

See also JuliaDiff/Diffractor.jl#292

src/eval.jl

@@ -15,6 +15,10 @@ function build_codeinfo(ir::IR)
     push!(ci.slotnames, Symbol(""))
     push!(ci.slotflags, 0)
   end
+  if isdefined(Base, :__has_internal_change) && Base.__has_internal_change(v"1.12-alpha", :codeinfonargs)
+    ci.nargs = length(arguments(ir)) + 1
+    ci.isva = false
+  end
   argument!(ir, at = 1)
   update!(ci, ir)
 end

src/reflection/dynamo.jl

@@ -100,6 +100,10 @@ function dynamo(cache, world, f, args...)
     m === nothing && error("Error looking up metadata for $f")
     m.code.method_for_inference_limit_heuristics = nothing
   end
+  if isdefined(Base, :__has_internal_change) && Base.__has_internal_change(v"1.12-alpha", :codeinfonargs)
+    m.code.nargs = 2
+    m.code.isva = true
+  end
   _self = splicearg!(ir)
   prewalk!(x -> x === self ? _self : x, ir)
   return update!(m.code, ir)
@@ -112,6 +116,10 @@ function dynamo_lambda(cache, world, f::Type{<:Lambda{S,I}}) where {S,I}
   closureargs!(ir)
   m = @meta world dummy(1)
   m.code.method_for_inference_limit_heuristics = nothing
+  if isdefined(Base, :__has_internal_change) && Base.__has_internal_change(v"1.12-alpha", :codeinfonargs)
+    m.code.nargs = 2
+    m.code.isva = true
+  end
   return update!(m.code, ir)
 end