fix: fix bugs with symbolic indexing and MTKParameters

Author: AayushSabharwal

src/systems/index_cache.jl

@@ -190,14 +190,16 @@ end
 function check_index_map(idxmap, sym)
     if (idx = get(idxmap, sym, nothing)) !== nothing
         return idx
-    elseif hasname(sym) && (idx = get(idxmap, getname(sym), nothing)) !== nothing
+    elseif !isa(sym, Symbol) && (!istree(sym) || operation(sym) !== getindex) &&
+           hasname(sym) && (idx = get(idxmap, getname(sym), nothing)) !== nothing
         return idx
     end
     dsym = default_toterm(sym)
     isequal(sym, dsym) && return nothing
     if (idx = get(idxmap, dsym, nothing)) !== nothing
         idx
-    elseif hasname(dsym) && (idx = get(idxmap, getname(dsym), nothing)) !== nothing
+    elseif !isa(dsym, Symbol) && (!istree(dsym) || operation(dsym) !== getindex) &&
+           hasname(dsym) && (idx = get(idxmap, getname(dsym), nothing)) !== nothing
         idx
     else
         nothing

src/systems/parameter_buffer.jl

@@ -224,13 +224,13 @@ function SymbolicIndexingInterface.parameter_values(p::MTKParameters, pind::Para
     @unpack portion, idx = pind
     i, j, k... = idx
     if portion isa SciMLStructures.Tunable
-        return p.tunable[i][j][k...]
+        return isempty(k) ? p.tunable[i][j] : p.tunable[i][j][k...]
     elseif portion isa SciMLStructures.Discrete
-        return p.discrete[i][j][k...]
+        return isempty(k) ? p.discrete[i][j] : p.discrete[i][j][k...]
     elseif portion isa SciMLStructures.Constants
-        return p.constant[i][j][k...]
+        return isempty(k) ? p.constant[i][j] : p.constant[i][j][k...]
     elseif portion === DEPENDENT_PORTION
-        return p.dependent[i][j][k...]
+        return isempty(k) ? p.dependent[i][j] : p.dependent[i][j][k...]
     elseif portion === NONNUMERIC_PORTION
         return isempty(k) ? p.nonnumeric[i][j] : p.nonnumeric[i][j][k...]
     else