Re-enable Enzyme tests on Julia v1.12

[ChrisRackauckas-Claude]

Summary

Enzyme tests have been disabled on Julia v1.12 and pre-release versions as part of the fix for issue #31.

Context

• Issue Like OrdinaryDiffEq.jl, create a separate test group for Enzyme tests #31 requested separating Enzyme tests into a separate test group (following the pattern from OrdinaryDiffEq.jl)
• Enzyme tests are currently disabled on Julia 1.12+ due to compatibility issues
• Tests are only running on Julia LTS (1.10.x) for now

Action Needed

When Enzyme has stable support for Julia 1.12:

1. Update the version check in test/runtests.jl to allow v1.12
2. Update .github/workflows/Tests.yml to add v1.12 to the Enzyme test matrix
3. Verify Enzyme tests pass on v1.12

Related

• Like OrdinaryDiffEq.jl, create a separate test group for Enzyme tests #31 (original issue that led to this)
• Enzyme.jl compatibility tracker: https://github.com/EnzymeAD/Enzyme.jl

cc @ChrisRackauckas

[ChrisRackauckas-Claude]

Investigation Findings

@ChrisRackauckas I investigated this issue and found:

Current State

1. Enzyme tests were never actually disabled - Looking at the codebase, there's no version check in test/runtests.jl or conditional test group handling. The tests currently run on all Julia versions including v1.12.

2. Issue Like OrdinaryDiffEq.jl, create a separate test group for Enzyme tests #31 was not implemented - The request to "separate Enzyme tests into a separate test group" was created but never actually done. This means there's nothing to "re-enable".

3. Enzyme now works on Julia 1.12 - I tested locally with Julia 1.12.3:

   • Enzyme 0.13.111 loads and runs successfully
   • OOP tests pass (60 tests)
   • In-place tests fail (7 errors) - but this is a known Enzyme limitation tracked in [Bug] Enzyme-based line search fails when storing dual variables in non-differentiable arrays #19

Test Results on Julia 1.12.3

Test Summary:                                  | Pass  Error  Total
LineSearch                                     |  374      7    381
  test/custom_optimizer_tests.jl               |  240           240
  test/root_finding_tests.jl                   |  134      7    141
    LineSearches.jl: Newton Raphson            |   90      5     95
      OOP Problem                              |   60            60  ✓
      In-Place Problem → AutoEnzyme()          |    0      5      5  ✗
    Native Line Search: Newton Raphson         |   44      2     46
      OOP Problem                              |   28            28  ✓
      In-Place Problem → AutoEnzyme()          |    0      2      2  ✗

The in-place errors are due to:

Enzyme.Compiler.EnzymeRuntimeActivityError: Duplicated Returns must be fully initialized before they are returned

This is the same issue as #19.

Recommendations

1. Close this issue as not applicable - Since Enzyme tests were never disabled on v1.12, there's nothing to re-enable.

2. OR implement Like OrdinaryDiffEq.jl, create a separate test group for Enzyme tests #31 first - If you want test group separation, that should be done in Like OrdinaryDiffEq.jl, create a separate test group for Enzyme tests #31. Once that's done, this issue becomes relevant for tracking when to add v1.12 back to the Enzyme test matrix.

3. Mark in-place Enzyme tests as broken - The in-place failures are not version-specific (they fail on all Julia versions due to [Bug] Enzyme-based line search fails when storing dual variables in non-differentiable arrays #19). Consider marking them as @test_broken to prevent CI failures.

Let me know how you'd like to proceed!