fix: promote buffer in _varmap_to_vars

Author: AayushSabharwal

src/variables.jl

@@ -201,16 +201,19 @@ function _varmap_to_vars(varmap::Dict, varlist; defaults = Dict(), check = false
     defaults = canonicalize_varmap(defaults; toterm)
     varmap = merge(defaults, varmap)
     values = Dict()
+
+    T = Union{}
     for var in varlist
         var = unwrap(var)
         val = unwrap(fixpoint_sub(var, varmap; operator = Symbolics.Operator))
         if !isequal(val, var)
             values[var] = val
+            T = promote_type(T, typeof(val))
         end
     end
     missingvars = setdiff(varlist, collect(keys(values)))
     check && (isempty(missingvars) || throw(MissingVariablesError(missingvars)))
-    return [values[unwrap(var)] for var in varlist]
+    return [T(values[unwrap(var)]) for var in varlist]
 end
 
 function varmap_with_toterm(varmap; toterm = Symbolics.diff2term)

test/odesystem.jl

@@ -1170,14 +1170,14 @@ end
 @test getname(unknowns(sys, x)) == :sys₊x
 @test size(unknowns(sys, x)) == size(x)
 
-# Issue#2667
+# Issue#2667 and Issue#2953
 @testset "ForwardDiff through ODEProblem constructor" begin
     @parameters P
     @variables x(t)
     sys = structural_simplify(ODESystem([D(x) ~ P], t, [x], [P]; name = :sys))
 
     function x_at_1(P)
-        prob = ODEProblem(sys, [x => 0.0], (0.0, 1.0), [sys.P => P])
+        prob = ODEProblem(sys, [x => P], (0.0, 1.0), [sys.P => P])
         return solve(prob, Tsit5())(1.0)
     end