Fix potential undefined variable in model compiler output

Author: penelopeysm

HISTORY.md

@@ -1,5 +1,9 @@
 # DynamicPPL Changelog
 
+## 0.38.5
+
+Made a small tweak to DynamicPPL's compiler output to avoid potential undefined variables when resuming model functions midway through (e.g. with Libtask in Turing's SMC/PG samplers).
+
 ## 0.38.4
 
 Improve performance of VarNamedVector. It should now be very nearly on par with Metadata for all models we've benchmarked on.

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.38.4"
+version = "0.38.5"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/compiler.jl

@@ -462,10 +462,12 @@ function generate_tilde(left, right)
             $(generate_tilde_assume(left, dist, vn))
         else
             # If `vn` is not in `argnames`, we need to make sure that the variable is defined.
-            if !$(DynamicPPL.inargnames)($vn, __model__)
-                $left = $(DynamicPPL.getconditioned_nested)(
+            $left = if !$(DynamicPPL.inargnames)($vn, __model__)
+                $(DynamicPPL.getconditioned_nested)(
                     __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
                 )
+            else
+                $left
             end
 
             $value, __varinfo__ = $(DynamicPPL.tilde_observe!!)(