From fc8f836a22b7a5cc87b741712b77f52613b5837f Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Sat, 6 Jun 2026 17:57:32 -0400
Subject: [PATCH 01/24] add basic macos support

---
 .github/workflows/ci.yml           | 89 ++++++++++++++++++++++++++++++
 README.md                          |  2 +-
 cmake/FindJulia.cmake              |  6 +-
 docs/src/index.md                  |  2 +-
 examples/trixi_controller_t8code.c |  6 +-
 utils/libtrixi-init-julia          | 80 +++++++++++++++++----------
 6 files changed, 150 insertions(+), 35 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 96694d49..8e61bf87 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -359,3 +359,92 @@ jobs:
         if: ${{ github.event_name == 'workflow_dispatch' && github.event.inputs.debug_enabled && always() }}
         uses: mxschmitt/action-tmate@v3
         timeout-minutes: 15
+
+  macos-smoke:
+    name: macos-latest - smoke - Julia 1.11 - ${{ github.event_name }}
+    runs-on: macos-latest
+    env:
+      JULIA_DEPOT_PATH: ~/.julia
+      T8CODE_VERSION: '3.0.1'
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Enable Julia cache
+        uses: julia-actions/cache@v3
+
+      - name: Enable t8code cache
+        id: cache-t8code
+        uses: actions/cache@v5
+        with:
+          path: ./t8code-local
+          key: ${{ runner.os }}-t8code-${{ env.T8CODE_VERSION }}
+
+      - name: Install Julia
+        uses: julia-actions/setup-julia@v3
+        with:
+          version: '1.11'
+
+      - name: Install dependencies available with Homebrew
+        run: |
+          brew install cmake gcc open-mpi hdf5
+
+      - name: Install t8code
+        if: steps.cache-t8code.outputs.cache-hit != 'true'
+        run: |
+          mkdir t8code-local
+          cd t8code-local
+          T8CODE_SOURCE=T8CODE-${T8CODE_VERSION}-Source
+          T8CODE_URL=https://github.com/DLR-AMR/t8code/releases/download
+          curl -L -O "$T8CODE_URL/v${T8CODE_VERSION}/$T8CODE_SOURCE.tar.gz"
+          tar xf "$T8CODE_SOURCE.tar.gz"
+          cmake -S "$T8CODE_SOURCE" -B build \
+                -DCMAKE_C_COMPILER=mpicc \
+                -DCMAKE_CXX_COMPILER=mpicxx \
+                -DCMAKE_Fortran_COMPILER=mpifort \
+                -DCMAKE_BUILD_TYPE=Release \
+                -DCMAKE_INSTALL_PREFIX="$PWD/prefix" \
+                -DT8CODE_BUILD_TESTS=OFF \
+                -DT8CODE_BUILD_TUTORIALS=OFF \
+                -DT8CODE_BUILD_EXAMPLES=OFF \
+                -DT8CODE_BUILD_BENCHMARKS=OFF \
+                -DT8CODE_ENABLE_MPI=ON \
+                -DT8CODE_BUILD_FORTRAN_INTERFACE=ON
+          cmake --build build --parallel 2
+          cmake --install build
+
+      - name: Build
+        run: |
+          cmake -S . -B build \
+                -DCMAKE_INSTALL_PREFIX="$PWD/install" \
+                -DCMAKE_BUILD_TYPE=Release \
+                -DT8CODE_ROOT="$PWD/t8code-local/prefix"
+          cmake --build build --parallel 2
+          cmake --install build
+
+      - name: Run examples
+        run: |
+          mkdir libtrixi-julia
+          cd libtrixi-julia
+          EXAMPLES_DIR=../install/share/libtrixi/LibTrixi.jl/examples
+          cp "$EXAMPLES_DIR/libelixir_t8code2d_euler_tracer_amr.jl" .
+          HDF5_PREFIX="$(brew --prefix hdf5)"
+          MPI_PREFIX="$(brew --prefix open-mpi)"
+          ../install/bin/libtrixi-init-julia .. \
+              --hdf5-library "$HDF5_PREFIX/lib/libhdf5.dylib" \
+              --mpi-library "$MPI_PREFIX/lib/libmpi.dylib" \
+              --t8code-library ../t8code-local/prefix/lib/libt8.dylib \
+              --julia-depot ~/.julia \
+              --skip-precompile \
+              --force
+          mkdir run-c run-f
+          PROJECT_DIR="$PWD"
+          LIBELIXIR_PATH="$PROJECT_DIR/libelixir_t8code2d_euler_tracer_amr.jl"
+          cd run-c
+          ../../build/examples/trixi_controller_t8code_c \
+              "$PROJECT_DIR" "$LIBELIXIR_PATH"
+          cd ../run-f
+          ../../build/examples/trixi_controller_t8code_f \
+              "$PROJECT_DIR" "$LIBELIXIR_PATH"
+        env:
+          LIBTRIXI_DEBUG: all
diff --git a/README.md b/README.md
index 771d1ae0..4e29cdd1 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 
 ### Prerequisites
 
-Currently, libtrixi is only developed and tested for Linux. Furthermore, the following
+Currently, libtrixi is developed and tested for Linux and macOS. Furthermore, the following
 software packages need to be made available locally before installing libtrixi:
 * [Julia](https://julialang.org/downloads/platform/) v1.8+
 * C compiler with support for C11 or later (e.g., [gcc](https://gcc.gnu.org/) or [clang](https://clang.llvm.org/))
diff --git a/cmake/FindJulia.cmake b/cmake/FindJulia.cmake
index 2fd2c20f..b33e8a1d 100644
--- a/cmake/FindJulia.cmake
+++ b/cmake/FindJulia.cmake
@@ -45,19 +45,19 @@ endif()
 # Get flags
 #
 execute_process(
-    COMMAND ${JULIA_SHARE}/julia-config.jl --cflags
+    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --cflags
     OUTPUT_VARIABLE JULIA_CFLAGS
     RESULT_VARIABLE RESULT
 )
 
 execute_process(
-    COMMAND ${JULIA_SHARE}/julia-config.jl --ldflags
+    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --ldflags
     OUTPUT_VARIABLE JULIA_LDFLAGS
     RESULT_VARIABLE RESULT
 )
 
 execute_process(
-    COMMAND ${JULIA_SHARE}/julia-config.jl --ldlibs
+    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --ldlibs
     OUTPUT_VARIABLE JULIA_LDLIBS
     RESULT_VARIABLE RESULT
 )
diff --git a/docs/src/index.md b/docs/src/index.md
index 62f1714c..e4c8a5f4 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -16,7 +16,7 @@
 
 ### Prerequisites
 
-Currently, libtrixi is only developed and tested for Linux. Furthermore, the following
+Currently, libtrixi is developed and tested for Linux and macOS. Furthermore, the following
 software packages need to be made available locally before installing libtrixi:
 * [Julia](https://julialang.org/downloads/platform/) v1.8+
 * C compiler with support for C11 or later (e.g., [gcc](https://gcc.gnu.org/) or [clang](https://clang.llvm.org/))
diff --git a/examples/trixi_controller_t8code.c b/examples/trixi_controller_t8code.c
index cebaaf30..af2d1981 100644
--- a/examples/trixi_controller_t8code.c
+++ b/examples/trixi_controller_t8code.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <inttypes.h>
 
 #include <t8.h>
 #include <t8_forest/t8_forest_general.h>
@@ -22,7 +23,10 @@ void t8_print_forest_information (t8_forest_t forest)
     global_num_elements = t8_forest_get_global_num_elements (forest);
 
     printf ("\n*** T8code ***  Local number of elements:\t%i\n", local_num_elements);
-    printf ("*** T8code ***  Global number of elements:\t%li\n", global_num_elements);
+
+    // Using PRId64 to print t8_gloidx_t portably across platforms
+    printf ("*** T8code ***  Global number of elements:\t%" PRId64 "\n",
+            global_num_elements);
 }
 
 
diff --git a/utils/libtrixi-init-julia b/utils/libtrixi-init-julia
index a7e0be6f..e8d6cc1a 100755
--- a/utils/libtrixi-init-julia
+++ b/utils/libtrixi-init-julia
@@ -53,30 +53,28 @@ optional arguments:
 
     --hdf5-library HDF5_LIBRARY
                     Path to the HDF5 shared library, i.e., something like
-                    'path/to/libhdf5.so'. If empty, Julia will try to figure out the path
-                    automatically. (default: '')
+                    'path/to/libhdf5.so' or 'path/to/libhdf5.dylib'. If empty, Julia
+                    will try to figure out the path automatically. (default: '')
 
     --mpi-library MPI_LIBRARY
                     Path to the MPI C shared library, i.e., something like
-                    'path/to/libmpi.so'. If empty, Julia will try to figure out the path
-                    automatically. (default: '')
+                    'path/to/libmpi.so' or 'path/to/libmpi.dylib'. If empty, Julia will
+                    try to figure out the path automatically. (default: '')
 
     --t8code-library T8CODE_LIBRARY
                     Path to the t8code shared library, i.e., something like
-                    'path/to/libt8.so'. If empty, Julia will try to figure out the path
-                    automatically. (default: '')
+                    'path/to/libt8.so' or 'path/to/libt8.dylib'. If empty, Julia will
+                    try to figure out the path automatically. (default: '')
 
     --p4est-library P4EST_LIBRARY
                     Path to the p4est shared library, i.e., something like
-                    'path/to/libp4est.so'.  If omitted, it will be assumed to be located
-                    next to the t8code library. (default: '\$(dirname \$T8CODE_LIBRARY)/
-                    libp4est.so')
+                    'path/to/libp4est.so' or 'path/to/libp4est.dylib'. If omitted, it
+                    will be assumed to be located next to the t8code library.
 
     --sc-library SC_LIBRARY
                     Path to the sc shared library, i.e., something like
-                    'path/to/libsc.so'. If omitted, it will be assumed to be located next
-                    to the t8code library. (default: '\$(dirname \$T8CODE_LIBRARY)/
-                    libsc.so')
+                    'path/to/libsc.so' or 'path/to/libsc.dylib'. If omitted, it will be
+                    assumed to be located next to the t8code library.
 EOF
 }
 
@@ -171,29 +169,50 @@ julia_exec="$LIBTRIXI_JULIA_EXEC"
 # Save Julia depot path
 julia_depot="$LIBTRIXI_JULIA_DEPOT"
 
-# Check if libhdf5.so was given by the user or try to find it using Julia
+# Determine platform shared library suffix
+case "$(uname -s)" in
+  Linux)
+    shared_library_suffix=so
+    ;;
+  Darwin)
+    shared_library_suffix=dylib
+    ;;
+  *)
+    shared_library_suffix=so
+    ;;
+esac
+
+# Check if the HDF5 library was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_HDF5_LIBRARY" ]; then
-  hdf5_libdir="$($julia_exec -e 'using Libdl; find_library("libhdf5") |> dlpath |> dirname |> println')"
-  if [ -z "$hdf5_libdir" ]; then
-    die "location of hdf5 library could not be determined automatically (use '--hdf5-library' instead)"
+  hdf5_library="$($julia_exec -e '
+using Libdl
+path = find_library("libhdf5")
+isempty(path) || println(dlpath(path))')"
+  if [ -z "$hdf5_library" ]; then
+    die "location of hdf5 library could not be determined; use --hdf5-library"
   fi
 else
-  hdf5_libdir="$(dirname $LIBTRIXI_HDF5_LIBRARY)"
+  hdf5_library="$LIBTRIXI_HDF5_LIBRARY"
 fi
-hdf5_library="$hdf5_libdir/libhdf5.so"
 if [ ! -f "$hdf5_library" ]; then
   die "hdf5 library '$hdf5_library' not found" 2
 fi
-hdf5_hl_library="$hdf5_libdir/libhdf5_hl.so"
+hdf5_libdir="$(dirname $hdf5_library)"
+hdf5_hl_library="$hdf5_libdir/libhdf5_hl.$shared_library_suffix"
 if [ ! -f "$hdf5_hl_library" ]; then
   die "hdf5 library '$hdf5_hl_library' not found" 2
 fi
 
 # Check if MPI library was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_MPI_LIBRARY" ]; then
-  mpi_library="$($julia_exec -e 'using Libdl; find_library(["libmpi", "libmpi_ibm", "msmpi", "libmpich", "libmpi_cray", "libmpitrampoline"]) |> dlpath |> println')"
+  mpi_library="$($julia_exec -e '
+using Libdl
+libraries = ["libmpi", "libmpi_ibm", "msmpi", "libmpich", "libmpi_cray",
+             "libmpitrampoline"]
+path = find_library(libraries)
+isempty(path) || println(dlpath(path))')"
   if [ -z "$mpi_library" ]; then
-    die "location of MPI library could not be determined automatically (use '--mpi-library' instead)"
+    die "location of MPI library could not be determined; use --mpi-library"
   fi
 else
   mpi_library="$LIBTRIXI_MPI_LIBRARY"
@@ -202,41 +221,44 @@ if [ ! -f "$mpi_library" ]; then
   die "MPI library '$mpi_library' not found" 2
 fi
 
-# Check if libt8.so was given by the user or try to find it using Julia
+# Check if libt8 was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_T8CODE_LIBRARY" ]; then
-  t8code_libdir="$($julia_exec -e 'using Libdl; find_library("libt8") |> dlpath |> dirname |> println')"
+  t8code_libdir="$($julia_exec -e '
+using Libdl
+path = find_library("libt8")
+isempty(path) || println(dirname(dlpath(path)))')"
   if [ -z "$t8code_libdir" ]; then
-    die "location of t8code library could not be determined automatically (use '--t8code-library' instead)"
+    die "location of t8code library could not be determined; use --t8code-library"
   fi
 else
   t8code_libdir="$(dirname $LIBTRIXI_T8CODE_LIBRARY)"
 fi
 t8code_libdir_abs="$(cd $t8code_libdir && pwd)"
-t8code_library="$t8code_libdir_abs/libt8.so"
+t8code_library="$t8code_libdir_abs/libt8.$shared_library_suffix"
 if [ ! -f "$t8code_library" ]; then
   die "t8code library '$t8code_library' not found" 2
 fi
 
-# Check if libp4est.so was given by the user or else assume it is next to libt8.so
+# Check if libp4est was given by the user or else assume it is next to libt8
 if [ -z "$LIBTRIXI_P4EST_LIBRARY" ]; then
   p4est_libdir="$t8code_libdir"
 else
   p4est_libdir="$(dirname $LIBTRIXI_P4EST_LIBRARY)"
 fi
 p4est_libdir_abs="$(cd $p4est_libdir && pwd)"
-p4est_library="$p4est_libdir_abs/libp4est.so"
+p4est_library="$p4est_libdir_abs/libp4est.$shared_library_suffix"
 if [ ! -f "$p4est_library" ]; then
   die "p4est library '$p4est_library' not found" 2
 fi
 
-# Check if libsc.so was given by the user or else assume it is next to libt8.so
+# Check if libsc was given by the user or else assume it is next to libt8
 if [ -z "$LIBTRIXI_SC_LIBRARY" ]; then
   sc_libdir="$t8code_libdir"
 else
   sc_libdir="$(dirname $LIBTRIXI_SC_LIBRARY)"
 fi
 sc_libdir_abs="$(cd $sc_libdir && pwd)"
-sc_library="$sc_libdir_abs/libsc.so"
+sc_library="$sc_libdir_abs/libsc.$shared_library_suffix"
 if [ ! -f "$sc_library" ]; then
   die "sc library '$sc_library' not found" 2
 fi

From 2e480fb4b08d88664778d805bfd43be82c84a1b6 Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Sat, 6 Jun 2026 18:09:03 -0400
Subject: [PATCH 02/24] find fortran compiler in ci

---
 .github/workflows/ci.yml | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8e61bf87..98586575 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -388,6 +388,17 @@ jobs:
       - name: Install dependencies available with Homebrew
         run: |
           brew install cmake gcc open-mpi hdf5
+          # Point Open MPI at Homebrew GCC's Fortran compiler
+          GFORTRAN="$(command -v gfortran || true)"
+          if [ -z "$GFORTRAN" ]; then
+              GFORTRAN="$(find "$(brew --prefix gcc)/bin" -name 'gfortran-*' | head -n 1)"
+          fi
+          if [ -z "$GFORTRAN" ]; then
+              echo "gfortran not found" >&2
+              exit 1
+          fi
+          echo "FC=$GFORTRAN" >> "$GITHUB_ENV"
+          echo "OMPI_FC=$GFORTRAN" >> "$GITHUB_ENV"
 
       - name: Install t8code
         if: steps.cache-t8code.outputs.cache-hit != 'true'

From 2e32c9354d4c879304a18f1d23264f9479afeab2 Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Sat, 6 Jun 2026 18:28:57 -0400
Subject: [PATCH 03/24] avoid doc deploy from fork PRs

---
 .github/workflows/Documenter.yml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/.github/workflows/Documenter.yml b/.github/workflows/Documenter.yml
index 808fc553..6f831f92 100644
--- a/.github/workflows/Documenter.yml
+++ b/.github/workflows/Documenter.yml
@@ -71,6 +71,9 @@ jobs:
           cd docs/doxygen
           doxygen
       - name: Deploy doxygen docs
+        if: >-
+          github.event_name != 'pull_request' ||
+          github.event.pull_request.head.repo.full_name == github.repository
         uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}

From 555949c675100819679d160db2e2723805a2d2b0 Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Mon, 15 Jun 2026 14:33:45 -0600
Subject: [PATCH 04/24] revert unnecessary diff

---
 utils/libtrixi-init-julia | 33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/utils/libtrixi-init-julia b/utils/libtrixi-init-julia
index e8d6cc1a..e1d77aa0 100755
--- a/utils/libtrixi-init-julia
+++ b/utils/libtrixi-init-julia
@@ -70,11 +70,13 @@ optional arguments:
                     Path to the p4est shared library, i.e., something like
                     'path/to/libp4est.so' or 'path/to/libp4est.dylib'. If omitted, it
                     will be assumed to be located next to the t8code library.
+                    (default: '\$(dirname \$T8CODE_LIBRARY)/libp4est.<suffix>')
 
     --sc-library SC_LIBRARY
                     Path to the sc shared library, i.e., something like
                     'path/to/libsc.so' or 'path/to/libsc.dylib'. If omitted, it will be
                     assumed to be located next to the t8code library.
+                    (default: '\$(dirname \$T8CODE_LIBRARY)/libsc.<suffix>')
 EOF
 }
 
@@ -182,22 +184,19 @@ case "$(uname -s)" in
     ;;
 esac
 
-# Check if the HDF5 library was given by the user or try to find it using Julia
+# Check if libhdf5 was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_HDF5_LIBRARY" ]; then
-  hdf5_library="$($julia_exec -e '
-using Libdl
-path = find_library("libhdf5")
-isempty(path) || println(dlpath(path))')"
-  if [ -z "$hdf5_library" ]; then
-    die "location of hdf5 library could not be determined; use --hdf5-library"
+  hdf5_libdir="$($julia_exec -e 'using Libdl; find_library("libhdf5") |> dlpath |> dirname |> println')"
+  if [ -z "$hdf5_libdir" ]; then
+    die "location of hdf5 library could not be determined automatically (use '--hdf5-library' instead)"
   fi
 else
-  hdf5_library="$LIBTRIXI_HDF5_LIBRARY"
+  hdf5_libdir="$(dirname $LIBTRIXI_HDF5_LIBRARY)"
 fi
+hdf5_library="$hdf5_libdir/libhdf5.$shared_library_suffix"
 if [ ! -f "$hdf5_library" ]; then
   die "hdf5 library '$hdf5_library' not found" 2
 fi
-hdf5_libdir="$(dirname $hdf5_library)"
 hdf5_hl_library="$hdf5_libdir/libhdf5_hl.$shared_library_suffix"
 if [ ! -f "$hdf5_hl_library" ]; then
   die "hdf5 library '$hdf5_hl_library' not found" 2
@@ -205,14 +204,9 @@ fi
 
 # Check if MPI library was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_MPI_LIBRARY" ]; then
-  mpi_library="$($julia_exec -e '
-using Libdl
-libraries = ["libmpi", "libmpi_ibm", "msmpi", "libmpich", "libmpi_cray",
-             "libmpitrampoline"]
-path = find_library(libraries)
-isempty(path) || println(dlpath(path))')"
+  mpi_library="$($julia_exec -e 'using Libdl; find_library(["libmpi", "libmpi_ibm", "msmpi", "libmpich", "libmpi_cray", "libmpitrampoline"]) |> dlpath |> println')"
   if [ -z "$mpi_library" ]; then
-    die "location of MPI library could not be determined; use --mpi-library"
+    die "location of MPI library could not be determined automatically (use '--mpi-library' instead)"
   fi
 else
   mpi_library="$LIBTRIXI_MPI_LIBRARY"
@@ -223,12 +217,9 @@ fi
 
 # Check if libt8 was given by the user or try to find it using Julia
 if [ -z "$LIBTRIXI_T8CODE_LIBRARY" ]; then
-  t8code_libdir="$($julia_exec -e '
-using Libdl
-path = find_library("libt8")
-isempty(path) || println(dirname(dlpath(path)))')"
+  t8code_libdir="$($julia_exec -e 'using Libdl; find_library("libt8") |> dlpath |> dirname |> println')"
   if [ -z "$t8code_libdir" ]; then
-    die "location of t8code library could not be determined; use --t8code-library"
+    die "location of t8code library could not be determined automatically (use '--t8code-library' instead)"
   fi
 else
   t8code_libdir="$(dirname $LIBTRIXI_T8CODE_LIBRARY)"

From bc09f6b63957caf4b91a3ae8f5fbf867f2ab1101 Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Mon, 15 Jun 2026 14:39:50 -0600
Subject: [PATCH 05/24] fix mistakes

---
 README.md         | 2 +-
 docs/src/index.md | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 4e29cdd1..cc57ae01 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 
 ### Prerequisites
 
-Currently, libtrixi is developed and tested for Linux and macOS. Furthermore, the following
+Currently, libtrixi is developed and tested for Linux and (experimentally) for macOS. Furthermore, the following
 software packages need to be made available locally before installing libtrixi:
 * [Julia](https://julialang.org/downloads/platform/) v1.8+
 * C compiler with support for C11 or later (e.g., [gcc](https://gcc.gnu.org/) or [clang](https://clang.llvm.org/))
diff --git a/docs/src/index.md b/docs/src/index.md
index e4c8a5f4..5ad8376b 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -16,7 +16,7 @@
 
 ### Prerequisites
 
-Currently, libtrixi is developed and tested for Linux and macOS. Furthermore, the following
+Currently, libtrixi is developed and tested for Linux and (experimentally) for macOS. Furthermore, the following
 software packages need to be made available locally before installing libtrixi:
 * [Julia](https://julialang.org/downloads/platform/) v1.8+
 * C compiler with support for C11 or later (e.g., [gcc](https://gcc.gnu.org/) or [clang](https://clang.llvm.org/))

From 63bb35a14368e1bd770b90983493bdb845cc0b6b Mon Sep 17 00:00:00 2001
From: Tristan Montoya <montoya.tristan@gmail.com>
Date: Mon, 15 Jun 2026 14:47:40 -0600
Subject: [PATCH 06/24] revert other unnecessary diff

---
 cmake/FindJulia.cmake | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/cmake/FindJulia.cmake b/cmake/FindJulia.cmake
index b33e8a1d..2fd2c20f 100644
--- a/cmake/FindJulia.cmake
+++ b/cmake/FindJulia.cmake
@@ -45,19 +45,19 @@ endif()
 # Get flags
 #
 execute_process(
-    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --cflags
+    COMMAND ${JULIA_SHARE}/julia-config.jl --cflags
     OUTPUT_VARIABLE JULIA_CFLAGS
     RESULT_VARIABLE RESULT
 )
 
 execute_process(
-    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --ldflags
+    COMMAND ${JULIA_SHARE}/julia-config.jl --ldflags
     OUTPUT_VARIABLE JULIA_LDFLAGS
     RESULT_VARIABLE RESULT
 )
 
 execute_process(
-    COMMAND ${JULIA_EXECUTABLE} ${JULIA_SHARE}/julia-config.jl --ldlibs
+    COMMAND ${JULIA_SHARE}/julia-config.jl --ldlibs
     OUTPUT_VARIABLE JULIA_LDLIBS
     RESULT_VARIABLE RESULT
 )

From 59b33326fb2cec1812a2e38c242884a9dfc74b1f Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Fri, 3 Jul 2026 23:31:56 +0200
Subject: [PATCH 07/24] check without GFORTRAN

---
 .github/workflows/ci.yml | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 98586575..b0c476b3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -388,17 +388,6 @@ jobs:
       - name: Install dependencies available with Homebrew
         run: |
           brew install cmake gcc open-mpi hdf5
-          # Point Open MPI at Homebrew GCC's Fortran compiler
-          GFORTRAN="$(command -v gfortran || true)"
-          if [ -z "$GFORTRAN" ]; then
-              GFORTRAN="$(find "$(brew --prefix gcc)/bin" -name 'gfortran-*' | head -n 1)"
-          fi
-          if [ -z "$GFORTRAN" ]; then
-              echo "gfortran not found" >&2
-              exit 1
-          fi
-          echo "FC=$GFORTRAN" >> "$GITHUB_ENV"
-          echo "OMPI_FC=$GFORTRAN" >> "$GITHUB_ENV"
 
       - name: Install t8code
         if: steps.cache-t8code.outputs.cache-hit != 'true'
@@ -433,7 +422,7 @@ jobs:
           cmake --build build --parallel 2
           cmake --install build
 
-      - name: Run examples
+      - name: Initialize project directory (test_type == 'package-compiler')
         run: |
           mkdir libtrixi-julia
           cd libtrixi-julia
@@ -448,6 +437,9 @@ jobs:
               --julia-depot ~/.julia \
               --skip-precompile \
               --force
+
+      - name: Run examples
+        run: |
           mkdir run-c run-f
           PROJECT_DIR="$PWD"
           LIBELIXIR_PATH="$PROJECT_DIR/libelixir_t8code2d_euler_tracer_amr.jl"

From ee20cb291b288dd70746f8e98bf922b2a218e97f Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Fri, 3 Jul 2026 23:42:06 +0200
Subject: [PATCH 08/24] fix

---
 .github/workflows/ci.yml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b0c476b3..b1dc38a6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -422,7 +422,7 @@ jobs:
           cmake --build build --parallel 2
           cmake --install build
 
-      - name: Initialize project directory (test_type == 'package-compiler')
+      - name: Initialize project directory
         run: |
           mkdir libtrixi-julia
           cd libtrixi-julia
@@ -440,6 +440,7 @@ jobs:
 
       - name: Run examples
         run: |
+          cd libtrixi-julia
           mkdir run-c run-f
           PROJECT_DIR="$PWD"
           LIBELIXIR_PATH="$PROJECT_DIR/libelixir_t8code2d_euler_tracer_amr.jl"

From be539aaa2955776571a5c70fccf9c3fdfbc56c39 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 11:42:57 +0200
Subject: [PATCH 09/24] try to integrate macos

---
 .github/workflows/ci.yml | 115 ++++++---------------------------------
 1 file changed, 17 insertions(+), 98 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b47d7832..f63988ff 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,6 +45,11 @@ jobs:
             arch: x64
             julia_version: '1.11'
             t8code_version: '4.0.0-26.07'
+          - os: macos-latest
+            test_type: smoke
+            arch: default
+            julia_version: '1.11'
+            t8code_version: '4.0.0-26.07'
     env:
       # Necessary for HDF5 to play nice with Julia
       LD_PRELOAD: /lib/x86_64-linux-gnu/libcurl.so.4
@@ -74,9 +79,11 @@ jobs:
         run: julia -e 'using InteractiveUtils; versioninfo(verbose=true)'
 
       - name: Update `apt-get`
+        if: ${{ matrix.os == 'ubuntu-latest' }}
         run: sudo apt-get update
 
       - name: Install dependencies available with `apt-get`
+        if: ${{ matrix.os == 'ubuntu-latest' }}
         # - MPI
         # - HDF5
         # - Google Test
@@ -87,6 +94,11 @@ jobs:
                                   libgtest-dev \
                                   lcov
 
+      - name: Install dependencies available with Homebrew
+        if: ${{ matrix.os == 'macos-latest' }}
+        run: |
+          brew install cmake gcc open-mpi hdf5
+
       - name: Install t8code
         if: steps.cache-t8code.outputs.cache-hit != 'true'
         run: |
@@ -120,7 +132,7 @@ jobs:
           mv ../prefix/PRIVATE_HEADER/* ../prefix/include/
 
       - name: Configure (test_type == 'regular')
-        if: ${{ matrix.test_type == 'regular' }}
+        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'smoke'}}
         run: |
           mkdir build
           cd build
@@ -144,13 +156,13 @@ jobs:
                    -DENABLE_TESTING=ON -DJULIA_PROJECT_PATH=../libtrixi-julia
 
       - name: Build
-        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' }}
+        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' || matrix.test_type == 'smoke' }}
         run: |
           cd build
           make -j 2
 
       - name: Install
-        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' }}
+        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' || matrix.test_type == 'smoke' }}
         run: |
           cd build
           make install
@@ -162,7 +174,7 @@ jobs:
           make -f MakefileExternal LIBTRIXI_PREFIX=$PWD/../install
 
       - name: Initialize project directory
-        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' }}
+        if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' || matrix.test_type == 'smoke' }}
         # Note that we set the Julia depot to `~/.julia` *ONLY* to make use of the
         # julia-actions/cache above (which unfortunately hardcoded the `~/.julia`
         # directory). For this reason, we also need to use `--force`
@@ -266,7 +278,7 @@ jobs:
           LIBTRIXI_DEBUG: all
 
       - name: Run examples (test_type == 'package-compiler')
-        if: ${{ matrix.test_type == 'package-compiler' }}
+        if: ${{ matrix.test_type == 'package-compiler' || matrix.test_type == 'smoke'}}
         run: |
           cd build/examples
           mpirun -n 2 trixi_controller_simple_c \
@@ -366,96 +378,3 @@ jobs:
         if: ${{ github.event_name == 'workflow_dispatch' && github.event.inputs.debug_enabled && always() }}
         uses: mxschmitt/action-tmate@v3
         timeout-minutes: 15
-
-  macos-smoke:
-    name: macos-latest - smoke - Julia 1.11 - ${{ github.event_name }}
-    runs-on: macos-latest
-    env:
-      JULIA_DEPOT_PATH: ~/.julia
-      T8CODE_VERSION: '3.0.1'
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v6
-
-      - name: Enable Julia cache
-        uses: julia-actions/cache@v3
-
-      - name: Enable t8code cache
-        id: cache-t8code
-        uses: actions/cache@v5
-        with:
-          path: ./t8code-local
-          key: ${{ runner.os }}-t8code-${{ env.T8CODE_VERSION }}
-
-      - name: Install Julia
-        uses: julia-actions/setup-julia@v3
-        with:
-          version: '1.11'
-
-      - name: Install dependencies available with Homebrew
-        run: |
-          brew install cmake gcc open-mpi hdf5
-
-      - name: Install t8code
-        if: steps.cache-t8code.outputs.cache-hit != 'true'
-        run: |
-          mkdir t8code-local
-          cd t8code-local
-          T8CODE_SOURCE=T8CODE-${T8CODE_VERSION}-Source
-          T8CODE_URL=https://github.com/DLR-AMR/t8code/releases/download
-          curl -L -O "$T8CODE_URL/v${T8CODE_VERSION}/$T8CODE_SOURCE.tar.gz"
-          tar xf "$T8CODE_SOURCE.tar.gz"
-          cmake -S "$T8CODE_SOURCE" -B build \
-                -DCMAKE_C_COMPILER=mpicc \
-                -DCMAKE_CXX_COMPILER=mpicxx \
-                -DCMAKE_Fortran_COMPILER=mpifort \
-                -DCMAKE_BUILD_TYPE=Release \
-                -DCMAKE_INSTALL_PREFIX="$PWD/prefix" \
-                -DT8CODE_BUILD_TESTS=OFF \
-                -DT8CODE_BUILD_TUTORIALS=OFF \
-                -DT8CODE_BUILD_EXAMPLES=OFF \
-                -DT8CODE_BUILD_BENCHMARKS=OFF \
-                -DT8CODE_ENABLE_MPI=ON \
-                -DT8CODE_BUILD_FORTRAN_INTERFACE=ON
-          cmake --build build --parallel 2
-          cmake --install build
-
-      - name: Build
-        run: |
-          cmake -S . -B build \
-                -DCMAKE_INSTALL_PREFIX="$PWD/install" \
-                -DCMAKE_BUILD_TYPE=Release \
-                -DT8CODE_ROOT="$PWD/t8code-local/prefix"
-          cmake --build build --parallel 2
-          cmake --install build
-
-      - name: Initialize project directory
-        run: |
-          mkdir libtrixi-julia
-          cd libtrixi-julia
-          EXAMPLES_DIR=../install/share/libtrixi/LibTrixi.jl/examples
-          cp "$EXAMPLES_DIR/libelixir_t8code2d_euler_tracer_amr.jl" .
-          HDF5_PREFIX="$(brew --prefix hdf5)"
-          MPI_PREFIX="$(brew --prefix open-mpi)"
-          ../install/bin/libtrixi-init-julia .. \
-              --hdf5-library "$HDF5_PREFIX/lib/libhdf5.dylib" \
-              --mpi-library "$MPI_PREFIX/lib/libmpi.dylib" \
-              --t8code-library ../t8code-local/prefix/lib/libt8.dylib \
-              --julia-depot ~/.julia \
-              --skip-precompile \
-              --force
-
-      - name: Run examples
-        run: |
-          cd libtrixi-julia
-          mkdir run-c run-f
-          PROJECT_DIR="$PWD"
-          LIBELIXIR_PATH="$PROJECT_DIR/libelixir_t8code2d_euler_tracer_amr.jl"
-          cd run-c
-          ../../build/examples/trixi_controller_t8code_c \
-              "$PROJECT_DIR" "$LIBELIXIR_PATH"
-          cd ../run-f
-          ../../build/examples/trixi_controller_t8code_f \
-              "$PROJECT_DIR" "$LIBELIXIR_PATH"
-        env:
-          LIBTRIXI_DEBUG: all

From 85e95687db837e743aa95a60a571667a5a271c17 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 13:37:21 +0200
Subject: [PATCH 10/24] check if mpifort works

---
 .github/workflows/ci.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f63988ff..f6043f84 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -113,6 +113,7 @@ jobs:
           cmake \
               -DCMAKE_C_COMPILER=mpicc \
               -DCMAKE_CXX_COMPILER=mpicxx \
+              -DCMAKE_Fortran_COMPILER=mpifort \
               -DCMAKE_BUILD_TYPE=Release \
               -DCMAKE_INSTALL_PREFIX="$PWD/../prefix" \
               -DT8CODE_BUILD_TESTS=OFF \

From a887f4734c07044130ed70d59a97f10450dea099 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 13:37:39 +0200
Subject: [PATCH 11/24] add comments

---
 .github/workflows/Documenter.yml   | 1 +
 examples/trixi_controller_t8code.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/Documenter.yml b/.github/workflows/Documenter.yml
index 5f01e13b..9a9a1c1b 100644
--- a/.github/workflows/Documenter.yml
+++ b/.github/workflows/Documenter.yml
@@ -71,6 +71,7 @@ jobs:
           cd docs/doxygen
           doxygen
       - name: Deploy doxygen docs
+        # Only deploy on merge to `main`
         if: >-
           github.event_name != 'pull_request' ||
           github.event.pull_request.head.repo.full_name == github.repository
diff --git a/examples/trixi_controller_t8code.c b/examples/trixi_controller_t8code.c
index ea2a243b..32c8bed7 100644
--- a/examples/trixi_controller_t8code.c
+++ b/examples/trixi_controller_t8code.c
@@ -24,7 +24,7 @@ void t8_print_forest_information (t8_forest_t forest)
 
     printf ("\n*** T8code ***  Local number of elements:\t%i\n", local_num_elements);
 
-    // Using PRId64 to print t8_gloidx_t portably across platforms
+    // Using special format specifier PRId64 to print t8_gloidx_t portably across platforms
     printf ("*** T8code ***  Global number of elements:\t%" PRId64 "\n",
             global_num_elements);
 }

From 2e65e47e23c23f582596f6be95e5608e54c4a24b Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 13:42:24 +0200
Subject: [PATCH 12/24] install gtest

---
 .github/workflows/ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f6043f84..563ffac0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -97,7 +97,7 @@ jobs:
       - name: Install dependencies available with Homebrew
         if: ${{ matrix.os == 'macos-latest' }}
         run: |
-          brew install cmake gcc open-mpi hdf5
+          brew install cmake gcc open-mpi hdf5 googletest
 
       - name: Install t8code
         if: steps.cache-t8code.outputs.cache-hit != 'true'

From fbb005029dffc25de13b26b495bc964efd314baf Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 14:21:40 +0200
Subject: [PATCH 13/24] conditionally adapt HDF5 prefix

---
 .github/workflows/ci.yml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 563ffac0..029a1060 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -182,12 +182,17 @@ jobs:
         # Still create subfolder `julia-depot`, which reflects the typical default
         # and is tested below
         run: |
+          if [ "${{ matrix.os }}" = "macos-latest" ]; then
+            HDF5_LIBRARY=$(brew --prefix hdf5)/lib/libhdf5.dylib
+          else
+            HDF5_LIBRARY=/usr/lib/x86_64-linux-gnu/hdf5/openmpi/libhdf5.so
+          fi
           mkdir libtrixi-julia
           cd libtrixi-julia
           cp ../install/share/libtrixi/LibTrixi.jl/examples/libelixir_* .
           mkdir julia-depot
           ../install/bin/libtrixi-init-julia .. \
-              --hdf5-library /usr/lib/x86_64-linux-gnu/hdf5/openmpi/libhdf5.so \
+              --hdf5-library "$HDF5_LIBRARY" \
               --t8code-library ../t8code-local/prefix/lib/libt8.so \
               --julia-depot ~/.julia \
               --force

From 453289b9501c696f37a79f3d9562d5e82c4fed6b Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 14:53:18 +0200
Subject: [PATCH 14/24] add MPI path for macos

---
 .github/workflows/ci.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 029a1060..29ec2040 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -184,6 +184,7 @@ jobs:
         run: |
           if [ "${{ matrix.os }}" = "macos-latest" ]; then
             HDF5_LIBRARY=$(brew --prefix hdf5)/lib/libhdf5.dylib
+            MPI_SWITCH="--mpi-library $(brew --prefix open-mpi)/lib/libmpi.dylib"
           else
             HDF5_LIBRARY=/usr/lib/x86_64-linux-gnu/hdf5/openmpi/libhdf5.so
           fi
@@ -193,6 +194,7 @@ jobs:
           mkdir julia-depot
           ../install/bin/libtrixi-init-julia .. \
               --hdf5-library "$HDF5_LIBRARY" \
+              "$MPI_SWITCH" \
               --t8code-library ../t8code-local/prefix/lib/libt8.so \
               --julia-depot ~/.julia \
               --force

From 12e3c64c4c584c5bf29b210c839859655597fb6a Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 15:15:40 +0200
Subject: [PATCH 15/24] use bash array instead

---
 .github/workflows/ci.yml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 29ec2040..7d703c68 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -184,9 +184,10 @@ jobs:
         run: |
           if [ "${{ matrix.os }}" = "macos-latest" ]; then
             HDF5_LIBRARY=$(brew --prefix hdf5)/lib/libhdf5.dylib
-            MPI_SWITCH="--mpi-library $(brew --prefix open-mpi)/lib/libmpi.dylib"
+            MPI_SWITCH=(--mpi-library "$(brew --prefix open-mpi)/lib/libmpi.dylib")
           else
             HDF5_LIBRARY=/usr/lib/x86_64-linux-gnu/hdf5/openmpi/libhdf5.so
+            MPI_SWITCH=()
           fi
           mkdir libtrixi-julia
           cd libtrixi-julia
@@ -194,7 +195,7 @@ jobs:
           mkdir julia-depot
           ../install/bin/libtrixi-init-julia .. \
               --hdf5-library "$HDF5_LIBRARY" \
-              "$MPI_SWITCH" \
+              "${MPI_SWITCH[@]}" \
               --t8code-library ../t8code-local/prefix/lib/libt8.so \
               --julia-depot ~/.julia \
               --force

From d0aae80deba9e05a079b3575bc43d1290a6ee1f9 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 15:53:47 +0200
Subject: [PATCH 16/24] add a Fortran example

---
 .github/workflows/ci.yml | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7d703c68..e0923d87 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -264,7 +264,7 @@ jobs:
           LIBTRIXI_DEBUG: all
           LD_PRELOAD: "" # Disable preloading libcurl.so since it does not work with the JLL-provided libhdf5.so
 
-      - name: Run examples
+      - name: Run examples (all)
         if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' }}
         run: |
           cd libtrixi-julia
@@ -286,13 +286,16 @@ jobs:
         env:
           LIBTRIXI_DEBUG: all
 
-      - name: Run examples (test_type == 'package-compiler')
+      - name: Run examples (some)
         if: ${{ matrix.test_type == 'package-compiler' || matrix.test_type == 'smoke'}}
         run: |
           cd build/examples
           mpirun -n 2 trixi_controller_simple_c \
               ../../libtrixi-julia \
               ../../LibTrixi.jl/examples/libelixir_p4est2d_euler_sedov.jl
+          mpirun -n 2 trixi_controller_t8code_f \
+              ../../libtrixi-julia \
+              ../../LibTrixi.jl/examples/libelixir_t8code2d_euler_tracer_amr.jl
         env:
           LIBTRIXI_DEBUG: all
 

From a93b6dc69b2f66cbd59ed6b7fff4b0138ab363fe Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Mon, 28 Sep 2026 16:43:05 +0200
Subject: [PATCH 17/24] Does PC work with t8code?

---
 .github/workflows/ci.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e0923d87..2e586d98 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -226,6 +226,7 @@ jobs:
           cd build
           cmake .. -DCMAKE_INSTALL_PREFIX=../install \
                    -DCMAKE_BUILD_TYPE=Debug \
+                   -DT8CODE_ROOT=$PWD/../t8code-local/prefix \
                    -DUSE_PACKAGE_COMPILER=ON \
                    -DJULIA_PROJECT_PATH=$PWD/../libtrixi-julia
 

From 7904222a441cd6958b48f73f2dc28ae02e686cc1 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:16:07 +0200
Subject: [PATCH 18/24] add option disabling fortran build

---
 CMakeLists.txt          | 73 +++++++++++++++++++++++++++--------------
 README.md               |  4 ++-
 docs/src/developers.md  |  2 +-
 docs/src/index.md       |  4 ++-
 examples/CMakeLists.txt | 11 +++++--
 5 files changed, 65 insertions(+), 29 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5376e94d..94631762 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,8 +23,18 @@ file(WRITE "${CMAKE_BINARY_DIR}/LIBTRIXI_VERSION" "${LIBTRIXI_VERSION}\n")
 project ( trixi VERSION ${LIBTRIXI_VERSION_MAJOR}.${LIBTRIXI_VERSION_MINOR}.${LIBTRIXI_VERSION_PATCH}
           DESCRIPTION "Interface library for using Trixi.jl from C/C++/Fortran" )
 
-# Enable C and Fortran
-enable_language(C Fortran)
+# Additional configuration options
+option( LIBTRIXI_BUILD_FORTRAN_API "Enable the build of the Fortran interface" ON )
+option( LIBTRIXI_ENABLE_TESTING "Build tests using Google Test (C) and test-drive (Fortran)" OFF )
+option( LIBTRIXI_USE_PACKAGE_COMPILER "Build standalone libtrixi.so using PackageCompiler.jl" )
+
+# Enable C always
+enable_language( C )
+
+# Optionally enable Fortran
+if( LIBTRIXI_BUILD_FORTRAN_API )
+    enable_language( Fortran )
+endif()
 
 # Enabling setting rpath for installation
 SET(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
@@ -47,8 +57,7 @@ endif()
 find_package( MPI REQUIRED )
 
 # Find Google Test and test-drive on demand
-option( ENABLE_TESTING "Build tests using Google Test (C) and test-drive (Fortran)" )
-if( ENABLE_TESTING )
+if( LIBTRIXI_ENABLE_TESTING )
     if ( NOT DEFINED JULIA_PROJECT_PATH )
         message( FATAL_ERROR "JULIA_PROJECT_PATH not set, tests will not work.")
     endif()
@@ -57,22 +66,23 @@ if( ENABLE_TESTING )
 
     find_package( GTest REQUIRED )
 
-    set ( TEST_DRIVE_FIND_METHOD fetch )
-    # Option TEST_DRIVE_BUILD_TESTING is hard-coded to ON, could be spared
-    find_package( test-drive REQUIRED )
+    if( LIBTRIXI_BUILD_FORTRAN_API )
+        set ( TEST_DRIVE_FIND_METHOD fetch )
+        # Option TEST_DRIVE_BUILD_TESTING is hard-coded to ON, could be spared
+        find_package( test-drive REQUIRED )
+    endif()
 endif()
 
-# Optionally use PackageCompiler.jl to build standalone libtrixi.so
-option( USE_PACKAGE_COMPILER "Build standalone libtrixi.so using PackageCompiler.jl" )
-
-# Fortran mod file location
-set(CMAKE_Fortran_MODULE_DIRECTORY ${CMAKE_BINARY_DIR})
+if( LIBTRIXI_BUILD_FORTRAN_API )
+    # Fortran mod file location
+    set(CMAKE_Fortran_MODULE_DIRECTORY ${CMAKE_BINARY_DIR})
+endif()
 
-if( USE_PACKAGE_COMPILER )
+if( LIBTRIXI_USE_PACKAGE_COMPILER )
     if ( NOT DEFINED JULIA_PROJECT_PATH )
         message( FATAL_ERROR "JULIA_PROJECT_PATH needs to be set for PackageCompiler.jl.")
     endif()
-    if ( ENABLE_TESTING )
+    if ( LIBTRIXI_ENABLE_TESTING )
         message( NOTICE "Testing is not supported when PackageCompiler is used.")
     endif()
 
@@ -89,10 +99,12 @@ if( USE_PACKAGE_COMPILER )
                         COMMAND ${CMAKE_COMMAND} -E copy ${PC_INIT_SOURCE} ${PC_INIT_BUILD}
                         DEPENDS ${PC_INIT_SOURCE} )
 
-    # Add a library target (libtrixi), only for Fortran module
-    add_library( ${PROJECT_NAME} OBJECT
-        src/api.f90
-    )
+    if( LIBTRIXI_BUILD_FORTRAN_API )
+        # Add a library target (libtrixi), only for Fortran module
+        add_library( ${PROJECT_NAME} OBJECT
+            src/api.f90
+        )
+    endif()
 
     # Custom command to run PackageCompiler.jl to produce libtrixi.so
     add_custom_command( OUTPUT ${PC_LIBTRIXI_SO}
@@ -123,12 +135,18 @@ else()
     # Library target
     add_library ( ${PROJECT_NAME} SHARED
         src/api.c
-        src/api.f90
         src/auxiliary.h
         src/auxiliary.c
         src/trixi.h
     )
 
+    # Build Fortran library target on demand
+    if( LIBTRIXI_BUILD_FORTRAN_API )
+        target_sources (${PROJECT_NAME} PRIVATE
+            src/api.f90
+        )
+    endif()
+
     # Include directories, private
     target_include_directories ( ${PROJECT_NAME} PRIVATE src )
 
@@ -141,7 +159,10 @@ else()
 
 
     # Include directories
-    target_include_directories( ${PROJECT_NAME} PRIVATE src ${JULIA_INCLUDE_DIRS} )
+    # PRIVATE: Do not include internal directory in projects building against libtrixi
+    # SYSTEM: Disable warnings/error from upstream libraries
+    target_include_directories( ${PROJECT_NAME} PRIVATE src )
+    target_include_directories( ${PROJECT_NAME} SYSTEM PRIVATE ${JULIA_INCLUDE_DIRS} )
 
     # Libraries to link
     target_link_libraries( ${PROJECT_NAME} PRIVATE ${JULIA_LIBRARY} )
@@ -160,13 +181,15 @@ else()
     add_library ( ${PROJECT_NAME}_tls OBJECT
         src/tls.c
     )
-    target_include_directories( ${PROJECT_NAME}_tls PRIVATE ${JULIA_INCLUDE_DIRS} )
+    target_include_directories( ${PROJECT_NAME}_tls SYSTEM ${JULIA_INCLUDE_DIRS} )
 
     # Add test on demand
-    if( ENABLE_TESTING )
+    if( LIBTRIXI_ENABLE_TESTING )
         enable_testing()
         add_subdirectory( test/c )
-        add_subdirectory( test/fortran )
+        if( LIBTRIXI_BUILD_FORTRAN_API )
+            add_subdirectory( test/fortran )
+        endif()
     endif()
 
 
@@ -183,7 +206,9 @@ set_target_properties ( ${PROJECT_NAME} PROPERTIES PUBLIC_HEADER src/trixi.h )
 # Common install configuration
 install( TARGETS ${PROJECT_NAME} )
 install( DIRECTORY LibTrixi.jl DESTINATION share/libtrixi PATTERN "lib" EXCLUDE )
-install( FILES ${CMAKE_Fortran_MODULE_DIRECTORY}/libtrixi.mod TYPE INCLUDE)
+if( LIBTRIXI_BUILD_FORTRAN_API )
+    install( FILES ${CMAKE_Fortran_MODULE_DIRECTORY}/libtrixi.mod TYPE INCLUDE)
+endif()
 install( PROGRAMS utils/libtrixi-init-julia TYPE BIN )
 
 # Add examples
diff --git a/README.md b/README.md
index cc57ae01..117acb1f 100644
--- a/README.md
+++ b/README.md
@@ -56,6 +56,8 @@ For building, `cmake` and its typical workflow is used.
     - Specifying the directory `install_directory` for later installation is optional.
     - Optional specification of build type sets some default compiler options for optimized
       or debug code.
+    - By default the Fortran-Interface is built; it may be excluded with
+      `-DLIBTRIXI_BUILD_FORTRAN_API=OFF`.
     - Building with t8code support is optional. It requires to pass
       `-DT8CODE_ROOT=<t8code_install_directory>`.
 
@@ -302,7 +304,7 @@ To try this out, perform the following steps:
     *using cmake*
     - Add
       ```
-      -DUSE_PACKAGE_COMPILER=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
+      -DLIBTRIXI_USE_PACKAGE_COMPILER=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
       ```
       to your cmake call (see above)
 3. From inside the `examples` folder you should be able to run the example (in parallel)
diff --git a/docs/src/developers.md b/docs/src/developers.md
index 0f6834c3..5ddd05f0 100644
--- a/docs/src/developers.md
+++ b/docs/src/developers.md
@@ -50,7 +50,7 @@ For testing the C interface of libtrixi we rely on [GoogleTest](https://google.g
 The tests are contained in `cpp`-files located under `test/c`. They are processed by `cmake` and made available via
 `ctest`, provided the options
 ```
--DENABLE_TESTING=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
+-DLIBTRIXI_ENABLE_TESTING=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
 ```
 are passed to `cmake` during configuration.
 The executables can then be found under `<build_directory>/test/c` (they will not be installed). To run them, execute
diff --git a/docs/src/index.md b/docs/src/index.md
index 5ad8376b..48baaa86 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -56,6 +56,8 @@ For building, `cmake` and its typical workflow is used.
     - Specifying the directory `install_directory` for later installation is optional.
     - Optional specification of build type sets some default compiler options for optimized
       or debug code.
+    - By default the Fortran-Interface is built; it may be excluded with
+      `-DLIBTRIXI_BUILD_FORTRAN_API=OFF`.
     - Building with t8code support is optional. It requires to pass
       `-DT8CODE_ROOT=<t8code_install_directory>`.
 
@@ -306,7 +308,7 @@ To try this out, perform the following steps:
     *using cmake*
     - Add
       ```
-      -DUSE_PACKAGE_COMPILER=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
+      -DLIBTRIXI_USE_PACKAGE_COMPILER=ON -DJULIA_PROJECT_PATH=<libtrixi-julia_directory>
       ```
       to your cmake call (see above)
 3. From inside the `examples` folder you should be able to run the example (in parallel)
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 508fb4bf..be992e3c 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -17,6 +17,11 @@ if ( NOT T8CODE_FOUND )
     list( FILTER EXAMPLES EXCLUDE REGEX "trixi_controller_baroclinic.*" )
 endif()
 
+if (NOT LIBTRIXI_BUILD_FORTRAN_API)
+    # Remove Fortran files if the the Fortran API is not build
+    list( FILTER EXAMPLES EXCLUDE REGEX ".*\.f90" )
+endif()
+
 foreach ( EXAMPLE ${EXAMPLES} )
 
     get_filename_component ( EXAMPLE_EXT ${EXAMPLE} EXT )
@@ -41,7 +46,7 @@ foreach ( EXAMPLE ${EXAMPLES} )
         ${TARGET_NAME}
         PRIVATE MPI::MPI_${EXAMPLE_LANG} ${PROJECT_NAME}
     )
-    if ( NOT USE_PACKAGE_COMPILER )
+    if ( NOT LIBTRIXI_USE_PACKAGE_COMPILER )
         target_link_libraries( ${TARGET_NAME} PRIVATE ${PROJECT_NAME}_tls )
     endif()
     if ( T8CODE_FOUND )
@@ -53,7 +58,9 @@ foreach ( EXAMPLE ${EXAMPLES} )
         ${TARGET_NAME}
         PRIVATE ${CMAKE_SOURCE_DIR}/src
     )
-    if ( T8CODE_FOUND )
+
+    if ( LIBTRIXI_BUILD_FORTRAN_API AND T8CODE_FOUND )
+        # Add the t8code include directory of the Fortran module file
         target_include_directories( ${TARGET_NAME} PRIVATE ${T8CODE_ROOT}/include/t8_fortran_interface/ )
     endif()
 

From 13e3ed15af1dca14b17253cc2e2cbb265efd6ea3 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:16:35 +0200
Subject: [PATCH 19/24] add a test with Fortran disabled

---
 .github/workflows/ci.yml | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2e586d98..416c1472 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -140,7 +140,17 @@ jobs:
           cmake .. -DCMAKE_INSTALL_PREFIX=../install \
                    -DCMAKE_BUILD_TYPE=Release \
                    -DT8CODE_ROOT=$PWD/../t8code-local/prefix \
-                   -DENABLE_TESTING=ON -DJULIA_PROJECT_PATH=../libtrixi-julia
+                   -DLIBTRIXI_ENABLE_TESTING=ON -DJULIA_PROJECT_PATH=../libtrixi-julia
+
+      - name: Configure without Fortran (test_type == 'regular')
+        if: ${{ matrix.test_type == 'regular' }}
+        run: |
+          mkdir build-nofortran
+          cd build-nofortran
+          cmake .. -DCMAKE_INSTALL_PREFIX=../install-nofortran \
+                   -DCMAKE_BUILD_TYPE=Release \
+                   -DT8CODE_ROOT=$PWD/../t8code-local/prefix \
+                   -LIBTRIXI_BUILD_FORTRAN_API=OFF
 
       - name: Configure (test_type == 'coverage')
         if: ${{ matrix.test_type == 'coverage' }}
@@ -154,13 +164,15 @@ jobs:
                    -DCMAKE_Fortran_FLAGS="-cpp --coverage -O0" \
                    -DCMAKE_EXE_LINKER_FLAGS="--coverage" \
                    -DCMAKE_SHARED_LINKER_FLAGS="--coverage" \
-                   -DENABLE_TESTING=ON -DJULIA_PROJECT_PATH=../libtrixi-julia
+                   -DLIBTRIXI_ENABLE_TESTING=ON -DJULIA_PROJECT_PATH=../libtrixi-julia
 
       - name: Build
         if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' || matrix.test_type == 'smoke' }}
         run: |
           cd build
           make -j 2
+          cd ../build-nofortran
+          make -j 2
 
       - name: Install
         if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' || matrix.test_type == 'smoke' }}
@@ -227,7 +239,7 @@ jobs:
           cmake .. -DCMAKE_INSTALL_PREFIX=../install \
                    -DCMAKE_BUILD_TYPE=Debug \
                    -DT8CODE_ROOT=$PWD/../t8code-local/prefix \
-                   -DUSE_PACKAGE_COMPILER=ON \
+                   -DLIBTRIXI_USE_PACKAGE_COMPILER=ON \
                    -DJULIA_PROJECT_PATH=$PWD/../libtrixi-julia
 
       - name: Build (test_type == 'package-compiler')
@@ -300,6 +312,16 @@ jobs:
         env:
           LIBTRIXI_DEBUG: all
 
+      - name: Run C example (Fortran API disabled)
+        if: ${{ matrix.test_type == 'regular'}}
+        run: |
+          cd build-nofortran
+          mpirun -n 2 trixi_controller_simple_c \
+              ../../libtrixi-julia \
+              ../../LibTrixi.jl/examples/libelixir_p4est2d_euler_sedov.jl
+        env:
+          LIBTRIXI_DEBUG: all
+
       - name: Check error handling of examples
         if: ${{ matrix.test_type == 'regular' || matrix.test_type == 'coverage' }}
         run: |

From 6be7ef255633188277fb7f317e6fd14c069917bd Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:17:48 +0200
Subject: [PATCH 20/24] temporarily switch to Julia 1.12

---
 .github/workflows/ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 416c1472..4fa1fe33 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
           - x64
         julia_version:
           - '1.10'
-          - '1.11'
+          - '1.12'
         t8code_version:
           - '4.0.0-26.07'
         include:

From 448fca646bbdcdab5fe7b88d36e6023e5df24e08 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:25:35 +0200
Subject: [PATCH 21/24] update minimum version

---
 CMakeLists.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 94631762..5ee8a13b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,7 +1,8 @@
 # Specify the minimum version
 #   3.9  required for regex submatches
 #   3.12 required for policy CMP0074 (using *_ROOT variables)
-cmake_minimum_required ( VERSION 3.12 )
+#   3.13 required for policy CMP0076 (target_sources() command converts relative paths to absolute)
+cmake_minimum_required ( VERSION 3.13 )
 
 # Reconfigure if Project.toml has changed
 set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS "${CMAKE_SOURCE_DIR}/LibTrixi.jl/Project.toml")

From fed382510f85350112c912bc045630396b5d8446 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:25:50 +0200
Subject: [PATCH 22/24] SYSTEM PRIVATE?

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5ee8a13b..2e55aec9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -182,7 +182,7 @@ else()
     add_library ( ${PROJECT_NAME}_tls OBJECT
         src/tls.c
     )
-    target_include_directories( ${PROJECT_NAME}_tls SYSTEM ${JULIA_INCLUDE_DIRS} )
+    target_include_directories( ${PROJECT_NAME}_tls SYSTEM PRIVATE ${JULIA_INCLUDE_DIRS} )
 
     # Add test on demand
     if( LIBTRIXI_ENABLE_TESTING )

From 3eb3d369a10b7e37645dbfa06483e205acf19029 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 11:27:47 +0200
Subject: [PATCH 23/24] fix

---
 .github/workflows/ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4fa1fe33..03064040 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -150,7 +150,7 @@ jobs:
           cmake .. -DCMAKE_INSTALL_PREFIX=../install-nofortran \
                    -DCMAKE_BUILD_TYPE=Release \
                    -DT8CODE_ROOT=$PWD/../t8code-local/prefix \
-                   -LIBTRIXI_BUILD_FORTRAN_API=OFF
+                   -DLIBTRIXI_BUILD_FORTRAN_API=OFF
 
       - name: Configure (test_type == 'coverage')
         if: ${{ matrix.test_type == 'coverage' }}

From e809d472a8d07f0577c2118249a253d1b5a403f3 Mon Sep 17 00:00:00 2001
From: Benedict Geihe <bgeihe@uni-koeln.de>
Date: Tue, 29 Sep 2026 12:42:27 +0200
Subject: [PATCH 24/24] fix

---
 .github/workflows/ci.yml | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 03064040..efad5e87 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
           - x64
         julia_version:
           - '1.10'
-          - '1.12'
+          - '1.11'
         t8code_version:
           - '4.0.0-26.07'
         include:
@@ -171,7 +171,11 @@ jobs:
         run: |
           cd build
           make -j 2
-          cd ../build-nofortran
+
+      - name: Build without Fortran
+        if: ${{ matrix.test_type == 'regular' }}
+        run: |
+          cd build-nofortran
           make -j 2
 
       - name: Install
@@ -315,7 +319,7 @@ jobs:
       - name: Run C example (Fortran API disabled)
         if: ${{ matrix.test_type == 'regular'}}
         run: |
-          cd build-nofortran
+          cd build-nofortran/examples
           mpirun -n 2 trixi_controller_simple_c \
               ../../libtrixi-julia \
               ../../LibTrixi.jl/examples/libelixir_p4est2d_euler_sedov.jl