Restore error when unknowns in the initialization system don't have guesses

docs/src/tutorials/initialization.md

@@ -195,7 +195,7 @@ long enough you will see that `λ = 0` is required for this equation, but since
 `λ = 1` we end up with a set of equations that are impossible to satisfy.
 
 !!! note
-
+    
     If you would prefer to have an error instead of a warning in the context of non-fully
     determined systems, pass the keyword argument `fully_determined = true` into the
     problem constructor. Additionally, any warning about not being fully determined can
@@ -278,7 +278,7 @@ sol = solve(iprob)
 ```
 
 !!! note
-
+    
     For more information on solving NonlinearProblems and NonlinearLeastSquaresProblems,
     check out the [NonlinearSolve.jl tutorials!](https://docs.sciml.ai/NonlinearSolve/stable/tutorials/getting_started/).
 

src/utils.jl

@@ -663,42 +663,43 @@ function promote_to_concrete(vs; tofloat = true, use_union = true)
         vs = Any[vs...]
     end
     T = eltype(vs)
-    if Base.isconcretetype(T) && (!tofloat || T === float(T)) # nothing to do
-        return vs
-    else
-        sym_vs = filter(x -> SymbolicUtils.issym(x) || SymbolicUtils.iscall(x), vs)
-        isempty(sym_vs) || throw_missingvars_in_sys(sym_vs)
-
-        C = nothing
-        for v in vs
-            E = typeof(v)
-            if E <: Number
-                if tofloat
-                    E = float(E)
-                end
-            end
-            if C === nothing
-                C = E
-            end
-            if use_union
-                C = Union{C, E}
-            else
-                @assert C==E "`promote_to_concrete` can't make type $E uniform with $C"
-                C = E
-            end
-        end
 
-        y = similar(vs, C)
-        for i in eachindex(vs)
-            if (vs[i] isa Number) & tofloat
-                y[i] = float(vs[i]) #needed because copyto! can't convert Int to Float automatically
-            else
-                y[i] = vs[i]
+    # return early if there is nothing to do
+    #Base.isconcretetype(T) && (!tofloat || T === float(T)) && return vs # TODO: disabled float(T) to restore missing errors in https://github.com/SciML/ModelingToolkit.jl/issues/2873
+    Base.isconcretetype(T) && !tofloat && return vs
+
+    sym_vs = filter(x -> SymbolicUtils.issym(x) || SymbolicUtils.iscall(x), vs)
+    isempty(sym_vs) || throw_missingvars_in_sys(sym_vs)
+
+    C = nothing
+    for v in vs
+        E = typeof(v)
+        if E <: Number
+            if tofloat
+                E = float(E)
             end
         end
+        if C === nothing
+            C = E
+        end
+        if use_union
+            C = Union{C, E}
+        else
+            @assert C==E "`promote_to_concrete` can't make type $E uniform with $C"
+            C = E
+        end
+    end
 
-        return y
+    y = similar(vs, C)
+    for i in eachindex(vs)
+        if (vs[i] isa Number) & tofloat
+            y[i] = float(vs[i]) #needed because copyto! can't convert Int to Float automatically
+        else
+            y[i] = vs[i]
+        end
     end
+
+    return y
 end
 
 struct BitDict <: AbstractDict{Int, Int}

test/initializationsystem.jl

@@ -478,3 +478,11 @@ sys = structural_simplify(unsimp; fully_determined = false)
 sys = extend(sysx, sysy)
 @test length(equations(generate_initializesystem(sys))) == 2
 @test length(ModelingToolkit.guesses(sys)) == 1
+
+# https://github.com/SciML/ModelingToolkit.jl/issues/2873
+@testset "Error on missing defaults" begin
+    @variables x(t) y(t)
+    @named sys = ODESystem([x^2 + y^2 ~ 25, D(x) ~ 1], t)
+    ssys = structural_simplify(sys)
+    @test_throws ArgumentError ODEProblem(ssys, [x => 3], (0, 1), []) # y should have a guess
+end