feat: allow specifying problem_type using system metadata

src/problems/nonlinearproblem.jl

@@ -67,7 +67,8 @@ end
         check_length, check_compatibility, expression, kwargs...)
 
     kwargs = process_kwargs(sys; kwargs...)
-    args = (; f, u0, p, ptype = StandardNonlinearProblem())
+    ptype = getmetadata(sys, ProblemTypeCtx, StandardNonlinearProblem())
+    args = (; f, u0, p, ptype)
 
     return maybe_codegen_scimlproblem(expression, NonlinearProblem{iip}, args; kwargs...)
 end

src/problems/odeproblem.jl

@@ -77,7 +77,8 @@ end
     kwargs = process_kwargs(
         sys; expression, callback, eval_expression, eval_module, kwargs...)
 
-    args = (; f, u0, tspan, p, ptype = StandardODEProblem())
+    ptype = getmetadata(sys, ProblemTypeCtx, StandardODEProblem())
+    args = (; f, u0, tspan, p, ptype)
     maybe_codegen_scimlproblem(expression, ODEProblem{iip}, args; kwargs...)
 end
 

src/systems/system.jl

@@ -807,6 +807,16 @@ function SymbolicUtils.setmetadata(sys::AbstractSystem, k::DataType, v)
     @set sys.metadata = meta
 end
 
+"""
+    $(TYPEDSIGNATURES)
+
+Metadata key for systems containing the `problem_type` to be passed to the problem
+constructor, where applicable. For example, if `getmetadata(sys, ProblemTypeCtx, nothing)`
+is `CustomType()` then `ODEProblem(sys, ...).problem_type` will be `CustomType()` instead
+of `StandardODEProblem`.
+"""
+struct ProblemTypeCtx end
+
 """
     $(TYPEDSIGNATURES)
 """

test/nonlinearsystem.jl

@@ -434,3 +434,11 @@ end
     @test resid == [0.0]
     @test resid isa SVector
 end
+
+@testset "`ProblemTypeCtx`" begin
+    @variables x
+    @mtkcompile sys = System(
+        [0 ~ x^2 - 4x + 4]; metadata = [ModelingToolkit.ProblemTypeCtx => "A"])
+    prob = NonlinearProblem(sys, [x => 1.0])
+    @test prob.problem_type == "A"
+end

test/odesystem.jl

@@ -1566,3 +1566,11 @@ end
     @test !process_running(proc)
     kill(proc, Base.SIGKILL)
 end
+
+@testset "`ProblemTypeCtx`" begin
+    @variables x(t)
+    @mtkcompile sys = System(
+        [D(x) ~ x], t; metadata = [ModelingToolkit.ProblemTypeCtx => "A"])
+    prob = ODEProblem(sys, [x => 1.0], (0.0, 1.0))
+    @test prob.problem_type == "A"
+end