Improvement: Make FORTRAN interface work again and add tests for all its functions

.github/workflows/code_coverage.yml

@@ -91,13 +91,14 @@ jobs:
       run: export TEST_LEVEL_FLAG="-DT8CODE_TEST_LEVEL=${{ inputs.TEST_LEVEL }}"
            && echo TEST_LEVEL_FLAG="$TEST_LEVEL_FLAG" >> $GITHUB_ENV
     - name: build config variables
-      run: export CONFIG_OPTIONS="${TEST_LEVEL_FLAG} -DT8CODE_CODE_COVERAGE=ON -DT8CODE_USE_SYSTEM_SC=ON -DT8CODE_USE_SYSTEM_P4EST=ON -DT8CODE_BUILD_PEDANTIC=ON -DT8CODE_BUILD_WALL=ON -DT8CODE_BUILD_WERROR=ON -DT8CODE_ENABLE_MPI=$MPI -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DT8CODE_BUILD_FORTRAN_INTERFACE=ON -DT8CODE_BUILD_MESH_HANDLE=ON -DSC_DIR=$SC_PATH/install/cmake -DP4EST_DIR=$P4EST_PATH/install/cmake -DT8CODE_BUILD_BENCHMARKS=OFF -DT8CODE_BUILD_DOCUMENTATION=OFF -DT8CODE_BUILD_EXAMPLES=OFF -DT8CODE_BUILD_TUTORIALS=OFF"
+      run: export CONFIG_OPTIONS="${TEST_LEVEL_FLAG} -DCMAKE_Fortran_COMPILER=mpifort -DT8CODE_CODE_COVERAGE=ON -DT8CODE_USE_SYSTEM_SC=ON -DT8CODE_USE_SYSTEM_P4EST=ON -DT8CODE_BUILD_PEDANTIC=ON -DT8CODE_BUILD_WALL=ON -DT8CODE_BUILD_WERROR=ON -DT8CODE_ENABLE_MPI=$MPI -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DT8CODE_BUILD_FORTRAN_INTERFACE=ON -DT8CODE_BUILD_MESH_HANDLE=ON -DSC_DIR=$SC_PATH/install/cmake -DP4EST_DIR=$P4EST_PATH/install/cmake -DT8CODE_BUILD_BENCHMARKS=OFF -DT8CODE_BUILD_DOCUMENTATION=OFF -DT8CODE_BUILD_EXAMPLES=OFF -DT8CODE_BUILD_TUTORIALS=OFF"
         && echo CONFIG_OPTIONS="$CONFIG_OPTIONS" >> $GITHUB_ENV
     # cmake
     - name: echo cmake line
-      run: echo cmake ../ $CONFIG_OPTIONS
+      run: echo cmake ../ $CONFIG_OPTIONS -DCMAKE_Fortran_FLAGS="-fprofile-arcs -ftest-coverage" 
+    # Note: Adding DCMAKE_Fortran_FLAGS here is a workaround because the blank space between the compiler flags causes trouble otherwise.
     - name: cmake
-      run: mkdir build && cd build && cmake ../ $CONFIG_OPTIONS
+      run: mkdir build && cd build && cmake ../ $CONFIG_OPTIONS -DCMAKE_Fortran_FLAGS="-fprofile-arcs -ftest-coverage" 
     - name: OnFailUploadLog
       if: failure()
       uses: actions/upload-artifact@v6
@@ -117,4 +118,4 @@ jobs:
         fail_ci_if_error: true
         disable_search: true
         token: ${{ secrets.CODE_COV }}
-
+

api/t8_fortran_interface/CMakeLists.txt

@@ -1,6 +1,6 @@
 # Link in C-Fortran interface file into libt8.
 target_sources( T8 PRIVATE t8_fortran_interface.c )
-target_sources( T8 PRIVATE t8_fortran_interface_mod.f90 )
+target_sources( T8 PRIVATE t8_fortran_interface_mod.f90 t8_fortran_example_adapt_mod.f90 )
 
 
 # Add this directory to header search path.

api/t8_fortran_interface/t8_fortran_example_adapt_mod.f90

@@ -0,0 +1,48 @@
+! This file is part of t8code.
+! t8code is a C library to manage a collection (a forest) of multiple
+! connected adaptive space-trees of general element classes in parallel.
+!
+! Copyright (C) 2026 the developers
+!
+! t8code is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 2 of the License, or
+! (at your option) any later version.
+!
+! t8code is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with t8code; if not, write to the Free Software Foundation, Inc.,
+! 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
+! This file contains a module with an example callback of the Fortran interface
+! that refines and coarsenes some elements based on their centroids' coordinates.
+module t8_fortran_example_adapt_mod
+    use t8_fortran_interface_mod
+
+contains
+
+      ! Example callback for adapting based on the centroid coordinates x, y, z.
+      function example_fortran_adapt_by_coordinates_callback(x, y, z, is_family) &
+            & result(ret) bind(c, name="example_fortran_adapt_by_coordinates_callback")
+            use, intrinsic :: ISO_C_BINDING, only: c_int, c_double
+            real(c_double), value :: x
+            real(c_double), value :: y
+            real(c_double), value :: z
+            integer(c_int), value :: is_family
+            integer(c_int) :: ret
+            ret = 0
+            if(x < 0.5d0 .and. y < 0.5d0 .and. z < 0.5d0) then
+                  ret = 1
+            elseif(x > 0.5d0 .and. y > 0.5d0) then
+                  if(is_family.ne.0) then
+                        ret = -1
+                  endif
+            endif
+
+      end function example_fortran_adapt_by_coordinates_callback
+
+end module t8_fortran_example_adapt_mod

api/t8_fortran_interface/t8_fortran_interface.c

@@ -21,10 +21,11 @@
 */
 
 #include <t8_fortran_interface.h>
-#include <t8_forest/t8_forest_general.h>
-#include <t8_forest/t8_forest_geometrical.h>
 #include <t8_cmesh/t8_cmesh_examples.h>
 #include <t8_cmesh/t8_cmesh_helpers.h>
+#include <t8_forest/t8_forest_general.h>
+#include <t8_forest/t8_forest_geometrical.h>
+#include <t8_forest/t8_forest_io.h>
 #include <t8_schemes/t8_scheme.h>
 #include <t8_schemes/t8_default/t8_default_c_interface.h>
 
@@ -51,12 +52,6 @@ t8_fortran_cmesh_commit (t8_cmesh_t cmesh, sc_MPI_Comm *comm)
   t8_cmesh_commit (cmesh, *comm);
 }
 
-void
-t8_fortran_cmesh_set_join_by_stash_noConn (t8_cmesh_t cmesh, const int do_both_directions)
-{
-  t8_cmesh_set_join_by_stash (cmesh, NULL, do_both_directions);
-}
-
 void
 t8_fortran_init_all (sc_MPI_Comm *comm)
 {
@@ -127,16 +122,14 @@ int
 t8_fortran_adapt_by_coordinates_callback (t8_forest_t forest, t8_forest_t forest_from, t8_locidx_t which_tree,
                                           const t8_eclass_t tree_class,
                                           __attribute__ ((unused)) t8_locidx_t lelement_id, const t8_scheme_c *scheme,
-                                          const int is_family, const int num_elements, t8_element_t *elements[])
+                                          const int is_family, __attribute__ ((unused)) const int num_elements,
+                                          t8_element_t *elements[])
 {
   t8_fortran_adapt_coordinate_callback callback
     = (t8_fortran_adapt_coordinate_callback) t8_forest_get_user_function (forest);
   double midpoint[3];
-  t8_forest_element_centroid (forest_from, which_tree, elements[0], midpoint);
-  t8_debugf ("Coord: %.2f\n", midpoint[0]);
-  int ret = callback (midpoint[0], midpoint[1], midpoint[2], num_elements > 0);
 
-  /* Coarsen if a family was given and return value is negative. */
+  /* If a family was given, form parent first to feed its centroid into the callback. */
   if (is_family) {
     /* The elements form a family */
     T8_ASSERT (t8_elements_are_family (scheme, tree_class, elements));
@@ -146,14 +139,16 @@ t8_fortran_adapt_by_coordinates_callback (t8_forest_t forest, t8_forest_t forest
     t8_element_get_parent (scheme, tree_class, elements[0], parent);
     /* Get the coordinates of the parent. */
     t8_forest_element_centroid (forest_from, which_tree, parent, midpoint);
-
-    ret = callback (midpoint[0], midpoint[1], midpoint[2], 1);
+    /* Deallocate parent element to avoid memory leakage. */
+    t8_element_destroy (scheme, tree_class, 1, &parent);
   }
   else {
     /* The elements do not form a family. */
-    /* Get the coordinates of the first element and call callback */
+    /* Get the coordinates of the first element.*/
     t8_forest_element_centroid (forest_from, which_tree, elements[0], midpoint);
-    ret = callback (midpoint[0], midpoint[1], midpoint[2], 0);
+  }
+  int ret = callback (midpoint[0], midpoint[1], midpoint[2], is_family);
+  if (!is_family) {
     T8_ASSERT (ret >= 0);
   }
   return ret;

api/t8_fortran_interface/t8_fortran_interface.h

@@ -21,11 +21,11 @@
 */
 
 /** \file t8_fortran_interface.h
- * In this file we provide a basic Fortran interface 
+ * In this file we provide a basic Fortran interface
  * for some functions of t8code.
  * Mostly, the C functions here are wrappers around more complex
  * t8code function.
- * We only export a minimum of the actual t8code functionality 
+ * We only export a minimum of the actual t8code functionality
  * to Fortran.
  */
 
@@ -73,19 +73,6 @@ t8_fortran_finalize ();
 void
 t8_fortran_cmesh_commit (t8_cmesh_t cmesh, sc_MPI_Comm *comm);
 
-/** This function calls t8_cmesh_set_join_by_stash with connectivity = NULL.
- * \param[in,out]   cmesh               Pointer to a t8code cmesh object. If set to NULL this argument is ignored.
- * \param[in]       do_both_directions  Compute the connectivity from both neighboring sides.
- *                                      Takes much longer to compute.
- *
- * \warning  This routine might be too expensive for very large meshes. In this case, 
- *           consider to use a fully featured mesh generator.
- *
- * \note This routine does not detect periodic boundaries.
-*/
-void
-t8_fortran_cmesh_set_join_by_stash_noConn (t8_cmesh_t cmesh, const int do_both_directions);
-
 /** Translate a fortran MPI communicator into a C MPI communicator
  * and return a pointer to it.
  * \param [in] Fcomm           Fortran MPI Communicator
@@ -125,7 +112,7 @@ t8_cmesh_new_periodic_tri_wrap (sc_MPI_Comm *Ccomm);
 t8_forest_t
 t8_forest_new_uniform_default (t8_cmesh_t cmesh, int level, int do_face_ghost, sc_MPI_Comm *comm);
 
-/** 
+/**
  * \param [in, out] forest     The forest
  * \param [in] recursive       A flag specifying whether adaptation is to be done recursively
  *                             or not. If the value is zero, adaptation is not recursive