Fix condition and fix in submodels

HISTORY.md

@@ -4,6 +4,24 @@
 
 **Breaking changes**
 
+### Submodels
+
+Variables in a submodel can now be conditioned and fixed in a correct way.
+See https://github.com/TuringLang/DynamicPPL.jl/issues/857 for a full illustration, but essentially it means you can now do this:
+
+```julia
+@model function inner()
+    x ~ Normal()
+    return y ~ Normal()
+end
+@model function outer()
+    return a ~ to_submodel(inner() | (x=1.0,))
+end
+```
+
+and the `inner.x` variable will be correctly conditioned.
+(Previously, you would have to condition `inner()` with the variable `a.x`, meaning that you would need to know what prefix to use before you had actually prefixed it.)
+
 ### AD testing utilities
 
 `DynamicPPL.TestUtils.AD.run_ad` now links the VarInfo by default.

docs/Project.toml

@@ -1,4 +1,5 @@
 [deps]
+AbstractPPL = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
 Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
 DataStructures = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"

docs/make.jl

@@ -24,7 +24,9 @@ makedocs(;
     format=Documenter.HTML(; size_threshold=2^10 * 400),
     modules=[DynamicPPL, Base.get_extension(DynamicPPL, :DynamicPPLMCMCChainsExt)],
     pages=[
-        "Home" => "index.md", "API" => "api.md", "Internals" => ["internals/varinfo.md"]
+        "Home" => "index.md",
+        "API" => "api.md",
+        "Internals" => ["internals/varinfo.md", "internals/submodel_condition.md"],
     ],
     checkdocs=:exports,
     doctest=false,

docs/src/api.md

@@ -78,7 +78,7 @@ decondition
 
 ## Fixing and unfixing
 
-We can also _fix_ a collection of variables in a [`Model`](@ref) to certain using [`fix`](@ref).
+We can also _fix_ a collection of variables in a [`Model`](@ref) to certain using [`DynamicPPL.fix`](@ref).
 
 This might seem quite similar to the aforementioned [`condition`](@ref) and its siblings,
 but they are indeed different operations:
@@ -89,19 +89,19 @@ but they are indeed different operations:
   - `fix`ed variables are considered to be _constant_, and are thus not included
     in any log-probability computations.
 
-The differences are more clearly spelled out in the docstring of [`fix`](@ref) below.
+The differences are more clearly spelled out in the docstring of [`DynamicPPL.fix`](@ref) below.
 
 ```@docs
-fix
+DynamicPPL.fix
 DynamicPPL.fixed
 ```
 
-The difference between [`fix`](@ref) and [`condition`](@ref) is described in the docstring of [`fix`](@ref) above.
+The difference between [`DynamicPPL.fix`](@ref) and [`DynamicPPL.condition`](@ref) is described in the docstring of [`DynamicPPL.fix`](@ref) above.
 
-Similarly, we can [`unfix`](@ref) variables, i.e. return them to their original meaning:
+Similarly, we can revert this with [`DynamicPPL.unfix`](@ref), i.e. return the variables to their original meaning:
 
 ```@docs
-unfix
+DynamicPPL.unfix
 ```
 
 ## Predicting