add downgrade workflow

.github/copilot-instructions.md

@@ -0,0 +1,44 @@
+# Copilot instructions for Trixi.jl
+
+## Big picture architecture
+- Trixi.jl is a **method-of-lines PDE framework**: elixirs define a spatial `semi` object, then `semidiscretize(semi, tspan)` creates an `ODEProblem` solved by SciML integrators.
+- Simulation setup is **code-first**, not config-file-first. Primary user entrypoint is `trixi_include(...)` (re-exported from `TrixiBase`), typically used with files in `examples/`.
+- The top-level assembly is in `src/Trixi.jl`; include order matters. Core domains are split into `src/equations/`, `src/meshes/`, `src/solvers/`, `src/semidiscretization/`, `src/time_integration/`, and callbacks.
+- `SemidiscretizationHyperbolic(mesh, equations, ic, solver; ...)` is the central composition pattern. Keep features modular by dispatching on mesh/equation/solver combinations.
+- Representative elixir structure: `examples/tree_2d_dgsem/elixir_advection_basic.jl`.
+
+## Mesh/solver boundaries you should respect
+- Mesh implementations are separated in `src/meshes/meshes.jl` (Tree/Structured/Unstructured/P4est/T8code/DGMulti families).
+- Solver entrypoints live in `src/solvers/solvers.jl` (`DGSEM`, `DGMulti`, parabolic solver includes).
+- Prefer adding specialized methods for valid combinations instead of forcing broad generic support across all mesh types.
+- Optional package features are implemented as Julia package extensions in `ext/` (e.g. `ext/TrixiCUDAExt.jl`, `ext/TrixiMakieExt.jl`).
+
+## Callbacks architecture
+- Callback code is split into `src/callbacks_step/` and `src/callbacks_stage/`, with exports and ordering defined in `src/callbacks_step/callbacks.jl`.
+- Step callbacks are typically `DiscreteCallback`/`PeriodicCallback` wrappers built from methods on callback types (see `SummaryCallback`, `AnalysisCallback`, `SaveSolutionCallback`, `StepsizeCallback`).
+- Preserve callback ordering in `CallbackSet`: summary/analysis/alive/save first, then AMR, then `StepsizeCallback`, then physics-specific post-step updates.
+- Interval checks should use accepted steps via `integrator.stats.naccept`; final-step behavior should use `isfinished(integrator)` from `src/callbacks_step/summary.jl`.
+- `SaveSolutionCallback` has both `interval` and `dt` modes (the latter via `PeriodicCallback`); keep both paths consistent when extending output.
+- Trixi has a separate stage-callback pipeline for `SimpleSSPRK33(stage_callbacks = (...))` in `src/time_integration/ssprk43.jl`; implement `init_callback`/`finalize_callback` in `src/time_integration/methods_SSP.jl` for new stage callback types.
+- For output extensions, prefer overload hooks like `get_element_variables!` (used by `AMRCallback`) instead of hard-coding into save routines.
+- Wire callbacks in elixirs as explicit variables plus `CallbackSet(...)` (see `examples/tree_2d_dgsem/elixir_advection_basic.jl`), and test via `@test_trixi_include` overrides in `test/test_trixi.jl` and callback-focused tests.
+
+## Developer workflows (project-specific)
+- Recommended local dev loop is REPL + Revise: `julia --project=run`, then `using Revise, Trixi`.
+- Run package tests via `Pkg.test("Trixi")`; CI shards tests using `TRIXI_TEST` in `test/runtests.jl`.
+- For targeted local runs, include specific files such as `include("test/test_tree_2d_part1.jl")`.
+- Threading/MPI behavior in tests is intentional; `test/runtests.jl` computes `TRIXI_NTHREADS` and `TRIXI_MPI_NPROCS` dynamically.
+- Keep new example elixirs covered by tests (see `examples/README.md` and existing `@trixi_testset` usage in `test/test_threaded.jl`).
+
+## Coding and testing conventions to follow
+- Formatting is enforced with JuliaFormatter (`.JuliaFormatter.toml`, SciML style, 4-space indent, max line length 92).
+- Use provided formatter helper: `utils/trixi-format.jl` (or `utils/pre-commit` hook flow).
+- Naming conventions are strict: `CamelCase` for types/modules, `snake_case` for functions/variables, mutating functions end with `!`.
+- Internal argument-order pattern matters: backend first (if present), then generally `mesh, equations, solver, cache`; modified argument first for mutating APIs.
+- Existing tests frequently use `@test_trixi_include` wrappers from `test/test_trixi.jl`; prefer this style for elixir-based regression tests.
+
+## Practical guidance for AI edits
+- When adding physics/numerics, update the appropriate domain file (`equations`, `solvers`, or `semidiscretization`) and add at least one elixir-backed test in the matching `test/test_*.jl` shard.
+- Preserve include organization and avoid moving files between subsystem directories unless required by design.
+- Use discoverable examples from `examples/` as templates rather than inventing new setup patterns.
+- If behavior is backend-specific (CUDA/MPI/weakdeps), gate it in extension files or existing backend dispatch paths instead of unconditional imports.

.github/workflows/downgrade.yml

@@ -0,0 +1,77 @@
+name: Downgrade
+
+on:
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - 'LICENSE.md'
+      - 'README.md'
+      - '.zenodo.json'
+      - '.github/workflows/CompatHelper.yml'
+      - '.github/workflows/TagBot.yml'
+      - 'docs/**'
+  pull_request:
+    paths-ignore:
+      - 'LICENSE.md'
+      - 'README.md'
+      - '.zenodo.json'
+      - '.github/workflows/CompatHelper.yml'
+      - '.github/workflows/TagBot.yml'
+      - 'docs/**'
+  workflow_dispatch:
+
+concurrency:
+  # Skip intermediate builds: always.
+  # Cancel intermediate builds: only if it is a pull request build.
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
+
+# needed to allow julia-actions/cache to delete old caches that it has created
+permissions:
+  actions: write
+  contents: read
+
+jobs:
+  downgrade_test:
+    if: "!contains(github.event.head_commit.message, 'skip ci')"
+    name: Downgrade - ${{ matrix.trixi_test }} - ${{ matrix.os }} - ${{ matrix.arch }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+          - '1.10'
+        os:
+          - ubuntu-latest
+        arch:
+          - x64
+        trixi_test:
+          - upstream
+    steps:
+      - uses: actions/checkout@v6
+      - uses: julia-actions/setup-julia@v2
+        with:
+          version: ${{ matrix.version }}
+          arch: ${{ matrix.arch }}
+      - run: julia -e 'using InteractiveUtils; versioninfo(verbose=true)'
+      - uses: julia-actions/cache@v2
+      - uses: julia-actions/julia-downgrade-compat@v2
+        with:
+          skip: LinearAlgebra,Printf,Test
+          projects: ., test
+          mode: forcedeps
+      # We run the tests manually instead of using julia-action/julia-builpkg and julia-action/julia-runtest or `Pkg.test`
+      # because otherwise the downgraded Manifest.toml is not used in the tests under julia <v1.12
+      # see also https://github.com/julia-actions/julia-downgrade-compat/blob/00f940b7be2b50389571ed016d603be561649103/README.md#L89
+      - name: Run tests
+        run: |
+          julia --project=test --color=yes -e '
+            import Pkg
+            Pkg.develop(Pkg.PackageSpec(path=pwd()))
+            Pkg.instantiate()
+            Pkg.status(; mode = Pkg.PKGMODE_MANIFEST)
+            include("test/runtests.jl")
+          '
+        env:
+          TRIXI_TEST: ${{ matrix.trixi_test }}

Project.toml

@@ -17,7 +17,7 @@ LinearAlgebra = "1"
 MuladdMacro = "0.2.4"
 Printf = "1"
 Roots = "2.1.6"
-Static = "1.1.1"
-StaticArrays = "1.9"
+Static = "1.2"
+StaticArrays = "1.9.8"
 Trixi = "0.15"
 julia = "1.10"

test/Project.toml

@@ -17,5 +17,5 @@ Roots = "2.1.6"
 Symbolics = "7.14"
 Test = "1"
 Trixi = "0.15"
-TrixiBottomTopography = "0.1"
+TrixiBottomTopography = "0.1.1"
 TrixiTest = "0.2.1"