supply missing externs

Changes

@@ -514,6 +514,9 @@ Working version
 
 ### Bug fixes:
 
+- # 12791: bytecode -custom supply missing externs
+  (Shayne Fletcher)
+
 - #12712, #12742: fix an assertion boundary case in `caml_reset_young_limit`
   (Jan Midtgaard, review by Guillaume Munch-Maccagnoni and KC Sivaramakrishnan)
 

bytecomp/symtable.ml

@@ -177,12 +177,20 @@ let output_primitive_table outchan =
     fprintf outchan "extern value %s(void);\n" prim.(i)
   done;
   fprintf outchan "typedef value (*c_primitive)(void);\n";
+  fprintf outchan "#if defined __cplusplus\n";
+  fprintf outchan "extern const c_primitive caml_builtin_cprim[] = {\n";
+  fprintf outchan "#else\n";
   fprintf outchan "const c_primitive caml_builtin_cprim[] = {\n";
+  fprintf outchan "#endif\n";
   for i = 0 to Array.length prim - 1 do
     fprintf outchan "  %s,\n" prim.(i)
   done;
   fprintf outchan "  0 };\n";
+  fprintf outchan "#if defined __cplusplus\n";
+  fprintf outchan "extern const char * const caml_names_of_builtin_cprim[] = {\n";
+  fprintf outchan "#else\n";
   fprintf outchan "const char * const caml_names_of_builtin_cprim[] = {\n";
+  fprintf outchan "#endif\n";
   for i = 0 to Array.length prim - 1 do
     fprintf outchan "  \"%s\",\n" prim.(i)
   done;

runtime/gen_primsc.sh

@@ -52,12 +52,20 @@ sed \
 
 # Generate the table of primitives
 echo
+echo '#if defined __cplusplus'
+echo 'extern const c_primitive caml_builtin_cprim[] = {'
+echo '#else'
 echo 'const c_primitive caml_builtin_cprim[] = {'
+echo '#endif'
 sed -e 's/.*/  (c_primitive) &,/' "$primitives"
 echo '  0 };'
 
 # Generate the table of primitive names
 echo
+echo '#if defined __cplusplus'
+echo 'extern const char * const caml_names_of_builtin_cprim[] = {'
+echo '#else'
 echo 'const char * const caml_names_of_builtin_cprim[] = {'
+echo '#endif'
 sed -e 's/.*/  "&",/' "$primitives"
 echo '  0 };'