Add JET.jl static analysis tests and improve type stability

- Add function barrier pattern to DataDrivenProblem constructor for type stability
- Add JET.jl static analysis tests for key functions
- Configure JET tests to run in CI environments
- Add JET as a test dependency with broad version compat

The new `_construct_datadrivenproblem` internal function ensures
that the type parameters (cType, probType) are known at compile time
through Val wrappers, improving type stability of problem construction.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: claude

Project.toml

@@ -1,7 +1,7 @@
 name = "DataDrivenDiffEq"
 uuid = "2445eb08-9709-466a-b3fc-47e12bd697a2"
-authors = ["Julius Martensen <julius.martensen@gmail.com>"]
 version = "1.12.0"
+authors = ["Julius Martensen <julius.martensen@gmail.com>"]
 
 [deps]
 CommonSolve = "38540f10-b2f7-11e9-35d8-d573e4eb0ff2"
@@ -30,6 +30,7 @@ CommonSolve = "0.2"
 DataInterpolations = "4, 5, 6, 7, 8"
 DiffEqBase = "6"
 DocStringExtensions = "0.7, 0.8, 0.9"
+JET = "0.9, 0.10, 0.11"
 MLUtils = "0.3, 0.4"
 ModelingToolkit = "11"
 OrdinaryDiffEqTsit5 = "1"
@@ -48,11 +49,12 @@ Symbolics = "7"
 julia = "1.10"
 
 [extras]
+JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"
 OrdinaryDiffEqTsit5 = "b1df2697-797e-41e3-8120-5422d3b24e4a"
 Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Test", "Random", "SafeTestsets", "Pkg", "OrdinaryDiffEqTsit5"]
+test = ["Test", "Random", "SafeTestsets", "Pkg", "OrdinaryDiffEqTsit5", "JET"]

src/problem/type.jl

@@ -114,6 +114,15 @@ end
 
 Base.eltype(::AbstractDataDrivenProblem{T}) where {T} = T
 
+# Internal constructor that is type-stable once cType and probType are known
+# This function barrier ensures the inner construction is fully specialized
+function _construct_datadrivenproblem(
+        ::Val{cType}, ::Val{probType}, dType::Type{T}, X, t, DX, Y, U, p, name
+    ) where {cType, probType, T}
+    promoted = _promote(X, t, DX, Y, U, p)
+    return DataDrivenProblem{T, cType, probType}(promoted..., name)
+end
+
 function DataDrivenProblem(
         probType, X, t, DX, Y, U, p; name = gensym(:DDProblem),
         kwargs...
@@ -131,7 +140,10 @@ function DataDrivenProblem(
         end
     end
 
-    return DataDrivenProblem{dType, cType, probType}(_promote(X, t, DX, Y, U, p)..., name)
+    # Use function barrier with Val types for type stability
+    return _construct_datadrivenproblem(
+        Val(cType), Val(probType), dType, X, t, DX, Y, U, p, name
+    )
 end
 
 function remake_problem(

test/jet_tests.jl

@@ -0,0 +1,68 @@
+using DataDrivenDiffEq
+using JET
+using Test
+
+# Note: JET analysis on symbolic packages can be slow and may report many
+# false positives from the underlying symbolic infrastructure (Symbolics.jl,
+# ModelingToolkit.jl). This test file focuses on core DataDrivenDiffEq
+# functionality with concrete types to catch actual type stability issues.
+#
+# We use @test_opt with target_modules to only check DataDrivenDiffEq code,
+# and we use broken=true for tests that detect expected polymorphic behavior
+# (like problem type dispatch) rather than actual bugs.
+
+@testset "JET Static Analysis" begin
+    @testset "Basis generator type stability" begin
+        # Test basis generators with concrete types
+        # These should be fully type-stable as they don't involve symbolic computation
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.polynomial_basis(
+            2, 3
+        )
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.monomial_basis(2, 3)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.chebyshev_basis(2, 3)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.sin_basis(2, 3)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.cos_basis(2, 3)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.fourier_basis(2, 3)
+    end
+
+    @testset "Problem accessor type stability" begin
+        X = rand(2, 10)
+        t = collect(1.0:10.0)
+        DX = rand(2, 10)
+
+        prob = ContinuousDataDrivenProblem(X, t, DX)
+
+        # Test simple accessor functions that should be type-stable
+        # These accessors only check type parameters, not field values
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.is_autonomous(prob)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.is_discrete(prob)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.is_continuous(prob)
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq.is_direct(prob)
+        # Note: has_timepoints checks isempty on AbstractVector field, which has
+        # expected runtime dispatch due to the abstract field type design choice
+    end
+
+    @testset "Internal constructor type stability" begin
+        # Test the internal type-stable constructor directly
+        X = rand(2, 10)
+        t = collect(1.0:10.0)
+        DX = rand(2, 10)
+        Y = Matrix{Float64}(undef, 0, 0)
+        U = Matrix{Float64}(undef, 0, 0)
+        p = Float64[]
+
+        # The internal constructor should be fully type-stable
+        @test_opt target_modules = (DataDrivenDiffEq,) DataDrivenDiffEq._construct_datadrivenproblem(
+            Val(false),
+            Val(DataDrivenDiffEq.DDProbType(3)),
+            Float64,
+            X,
+            t,
+            DX,
+            Y,
+            U,
+            p,
+            :test
+        )
+    end
+end

test/runtests.jl

@@ -41,6 +41,14 @@ end
                 include("./commonsolve/commonsolve.jl")
             end
         end
+
+        # Run JET analysis tests only in CI or when GROUP explicitly includes JET
+        # Note: JET tests may take longer due to static analysis overhead
+        if get(ENV, "CI", "false") == "true" || get(ENV, "RUN_JET_TESTS", "false") == "true"
+            @safetestset "JET Static Analysis" begin
+                include("./jet_tests.jl")
+            end
+        end
     else
         dev_subpkg(GROUP)
         subpkg_path = joinpath(dirname(@__DIR__), "lib", GROUP)