Allow merge to work on VarInfo with different distributions (#562)

* allow different distributions in merge

* added tests for merge with different distributions

* bump patch version since this is a bug

* Apply suggestions from code review

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: torfjelde

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.24.0"
+version = "0.24.1"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"

src/varinfo.jl

@@ -397,10 +397,9 @@ function merge_metadata(metadata_left::Metadata, metadata_right::Metadata)
             push!(ranges, r)
             offset = r[end]
             # `dists`: only valid if they're the same.
-            dists_left = getdist(metadata_left, vn)
-            dists_right = getdist(metadata_right, vn)
-            @assert dists_left == dists_right
-            push!(dists, dists_left)
+            dist_right = getdist(metadata_right, vn)
+            # Give precedence to `metadata_right`.
+            push!(dists, dist_right)
             # `orders`: giving precedence to `metadata_right`
             push!(orders, getorder(metadata_right, vn))
             # `flags`
@@ -418,8 +417,8 @@ function merge_metadata(metadata_left::Metadata, metadata_right::Metadata)
             push!(ranges, r)
             offset = r[end]
             # `dists`
-            dists_left = getdist(metadata_left, vn)
-            push!(dists, dists_left)
+            dist_left = getdist(metadata_left, vn)
+            push!(dists, dist_left)
             # `orders`
             push!(orders, getorder(metadata_left, vn))
             # `flags`
@@ -436,8 +435,8 @@ function merge_metadata(metadata_left::Metadata, metadata_right::Metadata)
             push!(ranges, r)
             offset = r[end]
             # `dists`
-            dists_right = getdist(metadata_right, vn)
-            push!(dists, dists_right)
+            dist_right = getdist(metadata_right, vn)
+            push!(dists, dist_right)
             # `orders`
             push!(orders, getorder(metadata_right, vn))
             # `flags`

test/varinfo.jl

@@ -594,6 +594,30 @@ DynamicPPL.getspace(::DynamicPPL.Sampler{MySAlg}) = (:s,)
                 end
             end
         end
+
+        @testset "different models" begin
+            @model function demo_merge_different_y()
+                x ~ Uniform()
+                return y ~ Normal()
+            end
+            @model function demo_merge_different_z()
+                x ~ Normal()
+                return z ~ Normal()
+            end
+            model_left = demo_merge_different_y()
+            model_right = demo_merge_different_z()
+
+            varinfo_left = VarInfo(model_left)
+            varinfo_right = VarInfo(model_right)
+
+            varinfo_merged = merge(varinfo_left, varinfo_right)
+            vns = [@varname(x), @varname(y), @varname(z)]
+            check_varinfo_keys(varinfo_merged, vns)
+
+            # Right has precedence.
+            @test varinfo_merged[@varname(x)] == varinfo_right[@varname(x)]
+            @test DynamicPPL.getdist(varinfo_merged, @varname(x)) isa Normal
+        end
     end
 
     @testset "VarInfo with selectors" begin