Compatibility with GAP.jl

* Added installation of GAPTypes.jl to configure when compilation
  with Julia is requested
* Made MPtr, Bag, and LargeBag Julia types instances of GapObj

configure.ac

@@ -497,6 +497,9 @@ AS_IF([test "x$with_julia" != xno ],[
   AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to obtain JULIA_LIBS from julia-config.jl])])
   JULIA_LIBS=${JULIA_LIBS//\'/}
   AC_MSG_RESULT([${JULIA_LIBS}])
+  AC_MSG_NOTICE([installing GAPTypes.jl])
+  ${JULIA} -e 'import Pkg; Pkg.add("GAPTypes")'
+  AS_IF([ test $? != 0 ], [AC_MSG_ERROR([failed to install GAPTypes.jl])])
 ],
 [
   AS_IF( [ test "x$with_gc" = xjulia ],

doc/changes/changes-4.10.xml

@@ -667,6 +667,11 @@ Specify the Julia binary instead of the Julia prefix
 Export Julia <C>CFLAGS</C>, <C>LDFLAGS</C>, and <C>LIBS</C> to <C>sysinfo.gap</C>
 (<URL><LinkText>&Hash;3248</LinkText><Link>https://github.com/gap-system/gap/pull/3248</Link></URL>).
 </Item>
+<Item>
+Change <C>MPtr</C> Julia type of &GAP; objects to be a subtype of the abstract Julia <C>GapObj</C> type
+provided by the Julia package <C>GAPTypes.jl</C>
+(<URL><LinkText>&Hash;3497</LinkText><Link>https://github.com/gap-system/gap/pull/3497</Link></URL>).
+</Item>
 </List>
 
 Improved and extended functionality:

src/julia_gc.c

@@ -817,6 +817,25 @@ void InitBags(UInt initial_size, Bag * stack_bottom, UInt stack_align)
     max_pool_obj_size = jl_gc_max_internal_obj_size();
     jl_gc_enable_conservative_gc_support();
     jl_init();
+
+    // Import GAPTypes module to have access to GapObj abstract type.
+    // Needs to be done before setting any GC states
+    jl_eval_string("import GAPTypes");
+    if (jl_exception_occurred()) {
+        Panic("could not import GAPTypes module into Julia");
+    }
+    // Get GapObj abstract julia type
+    jl_module_t * gaptypes_module =
+        (jl_module_t *)jl_get_global(jl_main_module, jl_symbol("GAPTypes"));
+    if (jl_exception_occurred()) {
+        Panic("Could not read global GAPTypes variable from Julia");
+    }
+    jl_datatype_t * gapobj_type =
+        (jl_datatype_t *)jl_get_global(gaptypes_module, jl_symbol("GapObj"));
+    if (jl_exception_occurred()) {
+        Panic("could not read GapObj variable from Julia");
+    }
+
     JuliaTLS = jl_get_ptls_states();
     // These callbacks potentially require access to the Julia
     // TLS and thus need to be installed after initialization.
@@ -828,14 +847,18 @@ void InitBags(UInt initial_size, Bag * stack_bottom, UInt stack_align)
 
     Module = jl_new_module(jl_symbol("ForeignGAP"));
     Module->parent = jl_main_module;
+
+    // Import GapObj type into ForeignGAP module
+    jl_module_use(Module, gaptypes_module, jl_symbol("GapObj"));
+
     jl_set_const(jl_main_module, jl_symbol("ForeignGAP"),
                  (jl_value_t *)Module);
     datatype_mptr = jl_new_foreign_type(
-        jl_symbol("MPtr"), Module, jl_any_type, MPtrMarkFunc, NULL, 1, 0);
-    datatype_bag = jl_new_foreign_type(jl_symbol("Bag"), Module, jl_any_type,
+        jl_symbol("MPtr"), Module, gapobj_type, MPtrMarkFunc, NULL, 1, 0);
+    datatype_bag = jl_new_foreign_type(jl_symbol("Bag"), Module, gapobj_type,
                                        BagMarkFunc, JFinalizer, 1, 0);
     datatype_largebag =
-        jl_new_foreign_type(jl_symbol("LargeBag"), Module, jl_any_type,
+        jl_new_foreign_type(jl_symbol("LargeBag"), Module, gapobj_type,
                             BagMarkFunc, JFinalizer, 1, 1);
 
     // export datatypes to Julia level