Handle :latestworld expr (#653)

* Handle `:latestworld` expr

These were added in JuliaLang/julia#56523.
This simply adds tracking for the world age to the interpreter, but
does not use it for anything. JuliaInterpreter's current model
of world age does not match Base anyway. We should fix that eventually,
but it's probably easier to do that once JuliaLang/julia#56509
and binding partitions are merged.

* 1.6 compat

Author: Keno

src/interpret.jl

@@ -550,6 +550,8 @@ function step_expr!(@nospecialize(recurse), frame::Frame, @nospecialize(node), i
                     error("unexpected error statement ", node)
                 elseif node.head === :incomplete
                     error("incomplete statement ", node)
+                elseif node.head === :latestworld
+                    frame.world = Base.get_world_counter()
                 else
                     rhs = eval_rhs(recurse, frame, node)
                 end

src/types.jl

@@ -253,8 +253,11 @@ mutable struct Frame
     caller::Union{Frame,Nothing}
     callee::Union{Frame,Nothing}
     last_codeloc::Int
+    # TODO: This is incompletely implemented
+    world::UInt
 end
-function Frame(framecode::FrameCode, framedata::FrameData, pc=1, caller=nothing)
+function Frame(framecode::FrameCode, framedata::FrameData, pc=1, caller=nothing,
+               world=isdefined(Base, :tls_world_age) ? Base.tls_world_age() : Base.get_world_counter())
     if length(junk_frames) > 0
         frame = pop!(junk_frames)
         frame.framecode = framecode
@@ -264,9 +267,10 @@ function Frame(framecode::FrameCode, framedata::FrameData, pc=1, caller=nothing)
         frame.caller = caller
         frame.callee = nothing
         frame.last_codeloc = 0
+        frame.world = world
         return frame
     else
-        return Frame(framecode, framedata, pc, 1, caller, nothing, 0)
+        return Frame(framecode, framedata, pc, 1, caller, nothing, 0, world)
     end
 end
 """