Fix compiler output for sub-variables of immutable data

HISTORY.md

@@ -1,5 +1,9 @@
 # DynamicPPL Changelog
 
+## 0.39.5
+
+Fixed a bug which prevented passing immutable data (such as NamedTuples or ordinary structs) as arguments to DynamicPPL models, or fixing the model on such data.
+
 ## 0.39.4
 
 Removed the internal functions `DynamicPPL.getranges`, `DynamicPPL.vector_getrange`, and `DynamicPPL.vector_getranges` (the new LogDensityFunction construction does exactly the same thing, so this specialised function was not needed).

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.39.4"
+version = "0.39.5"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/compiler.jl

@@ -463,6 +463,11 @@ function generate_tilde_literal(left, right)
     end
 end
 
+assign_or_set!!(lhs::Symbol, rhs) = AbstractPPL.drop_escape(:($lhs = $rhs))
+function assign_or_set!!(lhs::Expr, rhs)
+    return AbstractPPL.drop_escape(:($BangBang.@set!! $lhs = $rhs))
+end
+
 """
     generate_tilde(left, right)
 
@@ -474,27 +479,34 @@ function generate_tilde(left, right)
 
     # Otherwise it is determined by the model or its value,
     # if the LHS represents an observation
-    @gensym vn isassumption value dist
+    @gensym vn isassumption value dist supplied_val
 
     return quote
         $dist = $right
         $vn = $(DynamicPPL.resolve_varnames)($(make_varname_expression(left)), $dist)
         $isassumption = $(DynamicPPL.isassumption(left, vn))
         if $(DynamicPPL.isfixed(left, vn))
-            $left = $(DynamicPPL.getfixed_nested)(
-                __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
-            )
+            # $left may not be a simple varname, it might be x.a or x[1], in which case we
+            # need to use BangBang.@set!! to safely set it.
+            $(assign_or_set!!(
+                left,
+                :($(DynamicPPL.getfixed_nested)(
+                    __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
+                )),
+            ))
         elseif $isassumption
             $(generate_tilde_assume(left, dist, vn))
         else
             # If `vn` is not in `argnames`, then it's definitely been conditioned on (if
             # it's not in `argnames` and wasn't conditioned on, then `isassumption` would
             # be true).
-            $left = if $(DynamicPPL.inargnames)($vn, __model__)
-                # This is a no-op and looks redundant, but defining the compiler output this
-                # way ensures that the variable `$left` is always defined. See
-                # https://github.com/TuringLang/DynamicPPL.jl/pull/1110.
-                $left
+            # Note that it's important to always make sure that the variable `$supplied_val`
+            # is defined (by putting $supplied_val outside the if/else block), otherwise
+            # Libtask can trip up with variables that are only defined in one branch. See
+            # eg. https://github.com/TuringLang/DynamicPPL.jl/pull/1110 for a discussion of
+            # this.
+            $supplied_val = if $(DynamicPPL.inargnames)($vn, __model__)
+                $(maybe_view(left))
             else
                 $(DynamicPPL.getconditioned_nested)(
                     __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
@@ -504,10 +516,11 @@ function generate_tilde(left, right)
             $value, __varinfo__ = $(DynamicPPL.tilde_observe!!)(
                 __model__.context,
                 $(DynamicPPL.check_tilde_rhs)($dist),
-                $(maybe_view(left)),
+                $supplied_val,
                 $vn,
                 __varinfo__,
             )
+            $(assign_or_set!!(left, value))
             $value
         end
     end

test/compiler.jl

@@ -823,4 +823,17 @@ module Issue537 end
         end
         @test_logs (:warn, r"threadsafe evaluation") eval(e3)
     end
+
+    @testset "Immutable data as model arguments" begin
+        # https://github.com/TuringLang/DynamicPPL.jl/issues/1176
+        @model function nt(data)
+            m ~ Normal()
+            return data.x ~ Normal(m, 1.0)
+        end
+        data = (; x=5.0)
+        retval, vi = DynamicPPL.init!!(nt(data), VarInfo())
+        @test retval == 5.0
+        @test vi isa VarInfo
+        @test vi[@varname(m)] isa Real
+    end
 end

test/contexts.jl

@@ -312,6 +312,22 @@ Base.IteratorEltype(::Type{<:AbstractContext}) = Base.EltypeUnknown()
             @test model_fixed().m != m
             @test logprior(model_fixed, (; m)) == logprior(condition(model; s=s), (; m))
         end
+
+        @testset "Can fix immutable data safely" begin
+            # https://github.com/TuringLang/DynamicPPL.jl/issues/1176#issuecomment-3648871018
+            @model function ntfix()
+                m ~ Normal()
+                data = (; x=undef)
+                data.x ~ Normal(m, 1.0)
+                return data.x
+            end
+            fixm = DynamicPPL.fix(ntfix(), (; data=(; x=5.0)))
+            retval, vi = DynamicPPL.init!!(fixm, VarInfo())
+            # The fixed data should overwrite the NamedTuple that came before it
+            @test retval == 5.0
+            @test vi isa VarInfo
+            @test vi[@varname(m)] isa Real
+        end
     end
 
     @testset "PrefixContext + Condition/FixedContext interactions" begin