added error-handling of invalid broadcasting statements

Author: torfjelde

src/compiler.jl

@@ -235,6 +235,17 @@ function unwrap_right_left_vns(
     left::AbstractArray,
     vn::VarName,
 )
+    # Need to check that we don't end up double-counting log-probabilities.
+    combined_axes = Broadcast.combine_axes(left, right)
+    if prod(length, combined_axes) > length(left)
+        throw(
+            ArgumentError(
+                "a `.~` statement cannot result in a broadcasted expression with more elements than the left-hand side",
+            ),
+        )
+    end
+
+    # Extract the sub-varnames.
     vns = map(CartesianIndices(left)) do i
         return Accessors.IndexLens(Tuple(i)) ∘ vn
     end

test/compiler.jl

@@ -729,4 +729,13 @@ module Issue537 end
         res = model()
         @test res == (a=1, b=1, c=2, d=2, t=DynamicPPL.TypeWrap{Int}())
     end
+
+    @testset "invalid .~ expressions" begin
+        @model function demo_with_invalid_dot_tilde()
+            m = Matrix{Float64}(undef, 1, 2)
+            m .~ [Normal(); Normal()]
+        end
+
+        @test_throws ArgumentError demo_with_invalid_dot_tilde()()
+    end
 end