Fix for check_model on Julia <1.9 (#631)

* Added work-around for Julia v1.7 and lower only supporting `isassigned(x, ::Int...)`

* Add the work-around for `isassigned` for Julia <v1.9.0-alpha1 as it
seems that is when it was introduced JuliaLang/julia@c889fbc

* Update Project.toml

---------

Co-authored-by: Hong Ge <[email protected]>

Author: torfjelde

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.28"
+version = "0.28.1"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/debug_utils.jl

@@ -286,11 +286,19 @@ function record_varname!(context::DebugContext, varname::VarName, dist)
 end
 
 # tilde
+_isassigned(x::AbstractArray, i) = isassigned(x, i)
+# HACK(torfjelde): Julia v1.7 only supports `isassigned(::AbstractArray, ::Int...)`.
+# TODO(torfjelde): Determine exactly in which version this change was introduced.
+if VERSION < v"v1.9.0-alpha1"
+    _isassigned(x::AbstractArray, inds::Tuple) = isassigned(x, inds...)
+    _isassigned(x::AbstractArray, idx::CartesianIndex) = _isassigned(x, Tuple(idx))
+end
+
 _has_missings(x) = ismissing(x)
 function _has_missings(x::AbstractArray)
     # Can't just use `any` because `x` might contain `undef`.
     for i in eachindex(x)
-        if isassigned(x, i) && _has_missings(x[i])
+        if _isassigned(x, i) && _has_missings(x[i])
             return true
         end
     end