[Bug #19592] Fix ext/Setup support

After [1], using ext/Setup to link some, but not all extensions failed
during linking. I did not know about this option, and had assumed that
only `--with-static-linked-ext` builds can include statically linked
extensions.

Include the support code for statically linked extensions in all
configurations like before [1]. Initialize the table lazily to minimize
footprint on builds that have no statically linked extensions.

[1]: 790cf4b6d0475614afb127b416e87cfa39044d67 "Fix autoload status of
         statically linked extensions"

load.c

@@ -1032,8 +1032,10 @@ search_required(rb_vm_t *vm, VALUE fname, volatile VALUE *path, feature_func rb_
     }
     tmp = fname;
     type = rb_find_file_ext(&tmp, ft == 's' ? ruby_ext : loadable_ext);
-#if EXTSTATIC
+
-    if (!ft && type != 1) { // not already a feature and not found as a dynamic library
+    // Check if it's a statically linked extension when
+    // not already a feature and not found as a dynamic library.
+    if (!ft && type != 1 && vm->static_ext_inits) {
         VALUE lookup_name = tmp;
         // Append ".so" if not already present so for example "etc" can find "etc.so".
         // We always register statically linked extensions with a ".so" extension.
@@ -1048,7 +1050,7 @@ search_required(rb_vm_t *vm, VALUE fname, volatile VALUE *path, feature_func rb_
             return 's';
         }
     }
-#endif
+
     switch (type) {
       case 0:
         if (ft)
@@ -1087,19 +1089,18 @@ load_ext(VALUE path)
     return (VALUE)dln_load(RSTRING_PTR(path));
 }
 
-#if EXTSTATIC
 static bool
 run_static_ext_init(rb_vm_t *vm, const char *feature)
 {
     st_data_t key = (st_data_t)feature;
     st_data_t init_func;
-    if (st_delete(vm->static_ext_inits, &key, &init_func)) {
+
+    if (vm->static_ext_inits && st_delete(vm->static_ext_inits, &key, &init_func)) {
         ((void (*)(void))init_func)();
         return true;
     }
     return false;
 }
-#endif
 
 static int
 no_feature_p(rb_vm_t *vm, const char *feature, const char *ext, int rb, int expanded, const char **fn)
@@ -1203,11 +1204,9 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
             else if (!*ftptr) {
                 result = TAG_RETURN;
             }
-#if EXTSTATIC
             else if (found == 's' && run_static_ext_init(th->vm, RSTRING_PTR(path))) {
                 result = TAG_RETURN;
             }
-#endif
             else if (RTEST(rb_hash_aref(realpaths,
                                         realpath = rb_realpath_internal(Qnil, path, 1)))) {
                 result = 0;
@@ -1326,7 +1325,6 @@ rb_require(const char *fname)
     return rb_require_string(rb_str_new_cstr(fname));
 }
 
-#if EXTSTATIC
 static int
 register_init_ext(st_data_t *key, st_data_t *value, st_data_t init, int existing)
 {
@@ -1341,17 +1339,25 @@ register_init_ext(st_data_t *key, st_data_t *value, st_data_t init, int existing
     return ST_CONTINUE;
 }
 
+// Private API for statically linked extensions.
+// Used with the ext/Setup file, the --with-setup and
+// --with-static-linked-ext configuration option, etc.
 void
 ruby_init_ext(const char *name, void (*init)(void))
 {
+    st_table *inits_table;
     rb_vm_t *vm = GET_VM();
-    st_table *inits_table = vm->static_ext_inits;
 
     if (feature_provided(vm, name, 0))
         return;
+
+    inits_table = vm->static_ext_inits;
+    if (!inits_table) {
+        inits_table = st_init_strtable();
+        vm->static_ext_inits = inits_table;
+    }
     st_update(inits_table, (st_data_t)name, register_init_ext, (st_data_t)init);
 }
-#endif
 
 /*
  *  call-seq:

vm.c

@@ -4037,9 +4037,6 @@ Init_vm_objects(void)
     vm->mark_object_ary = rb_ary_hidden_new(128);
     vm->loading_table = st_init_strtable();
     vm->frozen_strings = st_init_table_with_size(&rb_fstring_hash_type, 10000);
-#if EXTSTATIC
-    vm->static_ext_inits = st_init_strtable();
-#endif
 }
 
 /* Stub for builtin function when not building YJIT units*/

vm_core.h

@@ -557,10 +557,6 @@ struct rb_iseq_struct {
 
 #define ISEQ_BODY(iseq) ((iseq)->body)
 
-#ifndef EXTSTATIC
-#define EXTSTATIC 0
-#endif
-
 #ifndef USE_LAZY_LOAD
 #define USE_LAZY_LOAD 0
 #endif
@@ -686,11 +682,9 @@ typedef struct rb_vm_struct {
     VALUE loaded_features_realpath_map;
     struct st_table *loaded_features_index;
     struct st_table *loading_table;
-#if EXTSTATIC
     // For running the init function of statically linked
     // extensions when they are loaded
     struct st_table *static_ext_inits;
-#endif
 
     /* signal */
     struct {