fix: fix major compile time regression due to concrete_getu

Author: AayushSabharwal

src/systems/problem_utils.jl

@@ -646,30 +646,40 @@ struct ReconstructInitializeprob{GP, GU}
     ugetter::GU
 end
 
+"""
+    $(TYPEDEF)
+
+A wrapper over an observed function which allows calling it on a problem-like object.
+`TD` determines whether the getter function is `(u, p, t)` (if `true`) or `(u, p)` (if
+`false`).
+"""
+struct ObservedWrapper{TD, F}
+    f::F
+end
+
+ObservedWrapper{TD}(f::F) where {TD, F} = ObservedWrapper{TD, F}(f)
+
+function (ow::ObservedWrapper{true})(prob)
+    ow.f(state_values(prob), parameter_values(prob), current_time(prob))
+end
+
+function (ow::ObservedWrapper{false})(prob)
+    ow.f(state_values(prob), parameter_values(prob))
+end
+
 """
     $(TYPEDSIGNATURES)
 
 Given an index provider `indp` and a vector of symbols `syms` return a type-stable getter
-function by splitting `syms` into contiguous buffers where the getter of each buffer
-is type-stable and constructing a function that calls and concatenates the results.
-"""
-function concrete_getu(indp, syms::AbstractVector)
-    # a list of contiguous buffer
-    split_syms = [Any[syms[1]]]
-    # the type of the getter of the last buffer
-    current = typeof(getu(indp, syms[1]))
-    for sym in syms[2:end]
-        getter = getu(indp, sym)
-        if typeof(getter) != current
-            # if types don't match, build a new buffer
-            push!(split_syms, [])
-            current = typeof(getter)
-        end
-        push!(split_syms[end], sym)
-    end
-    split_syms = Tuple(split_syms)
-    # the getter is now type-stable, and we can vcat it to get the full buffer
-    return Base.Fix1(reduce, vcat) ∘ getu(indp, split_syms)
+function.
+
+Note that the getter ONLY works for problem-like objects, since it generates an observed
+function. It does NOT work for solutions.
+"""
+Base.@nospecializeinfer function concrete_getu(indp, syms::AbstractVector)
+    @nospecialize
+    obsfn = build_explicit_observed_function(indp, syms; wrap_delays = false)
+    return ObservedWrapper{is_time_dependent(indp)}(obsfn)
 end
 
 """