# HG changeset patch
# User Markus Mützel <markus.muetzel@gmx.de>
# Date 1713010939 -7200
# Node ID f3ffee7cf47820a0857c26ed01e97f0e9264fbdf
# Parent  0d1a3c2ad9c62c324996f0d09e1aaaffe2b7ba39
build: Run test for polymorphic allocators if possible.

* m4/acinclude.m4 (OCTAVE_CHECK_STD_PMR_POLYMORPHIC_ALLOCATOR): On macOS, we
need to run an executable to check if polymorphic allocators are actually
working. Do that on all platforms (if possible). Fall back to a
compilation-only test when cross-compiling.

See: https://octave.discourse.group/t/5481/33

diff -r 0d1a3c2ad9c6 -r f3ffee7cf478 m4/acinclude.m4
--- a/m4/acinclude.m4	Sat Apr 13 12:13:34 2024 +0200
+++ b/m4/acinclude.m4	Sat Apr 13 14:22:19 2024 +0200
@@ -200,6 +200,47 @@
   AC_CACHE_CHECK([whether std::pmr::polymorphic_allocator is available],
     [octave_cv_std_pmr_polymorphic_allocator],
     [AC_LANG_PUSH(C++)
+    AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+      #include <cstdlib>
+      #include <memory_resource>
+      #include <vector>
+      class mx_memory_resource : public std::pmr::memory_resource
+      {
+      private:
+        void * do_allocate (std::size_t bytes, size_t /*alignment*/)
+        {
+          void *ptr = std::malloc (bytes);
+          if (! ptr)
+            throw std::bad_alloc ();
+            return ptr;
+        }
+        void do_deallocate (void* ptr, std::size_t /*bytes*/,
+                            std::size_t /*alignment*/)
+        {
+          std::free (ptr);
+        }
+        bool do_is_equal (const std::pmr::memory_resource& other) const noexcept
+        {
+          return this == dynamic_cast<const mx_memory_resource *> (&other);
+          return true;
+        }
+      };
+      mx_memory_resource the_mx_memory_resource;
+    ]], [[
+      std::pmr::vector<int> my_int_vec { &the_mx_memory_resource };
+    ]])],
+    octave_cv_std_pmr_polymorphic_allocator=yes,
+    octave_cv_std_pmr_polymorphic_allocator=no,
+    [## On macOS, we need to run an executable to check if polymorphic
+    ## allocators are working.
+    ## When cross-compiling to that target, the following test might succeed
+    ## even if polymorphic allocators are not actually implemented. In that
+    ## case, users would need to manually configure with
+    ## `--disable-std-pmr-polymorphic-allocator`.
+    ## When cross-compiling to any other target, the following test should be
+    ## giving accurate results.
+
+    ## FIXME: Is there a way to not repeat the same code from above?
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
       #include <cstdlib>
       #include <memory_resource>
@@ -230,7 +271,7 @@
       std::pmr::vector<int> my_int_vec { &the_mx_memory_resource };
     ]])],
     octave_cv_std_pmr_polymorphic_allocator=yes,
-    octave_cv_std_pmr_polymorphic_allocator=no)
+    octave_cv_std_pmr_polymorphic_allocator=no)])
     AC_LANG_POP(C++)
   ])
   if test $octave_cv_std_pmr_polymorphic_allocator = yes; then