From 73b2e0bf766ece2ec66a443d3d16294320941eb7 Mon Sep 17 00:00:00 2001
From: dearblue <dearblue@users.osdn.me>
Date: Sun, 2 Apr 2023 20:28:14 +0900
Subject: [PATCH] Shrink `<BUILD-DIR>/mrbgems/gem_init.c` if possible

If none of the GEMs have `mrblib/` or `src/` directories, generate `mrb_init_mrbgems()` which does nothing, and omit `mrb_final_mrbgems()`.

The impetus was to avoid `gem_funcs[]` becoming a zero-length array, which is not allowed by the C standard.
The problem is caused by #5938.
---
 tasks/mrbgems.rake | 94 ++++++++++++++++++++++++----------------------
 1 file changed, 49 insertions(+), 45 deletions(-)

diff --git a/tasks/mrbgems.rake b/tasks/mrbgems.rake
index 26d736bfd..686facb25 100644
--- a/tasks/mrbgems.rake
+++ b/tasks/mrbgems.rake
@@ -38,53 +38,57 @@ MRuby.each_target do
         f.puts %Q[#include <mruby/error.h>]
         f.puts %Q[#include <mruby/proc.h>]
         f.puts %Q[]
-        f.write gem_func_decls
-        f.puts %Q[]
-        f.puts %Q[static const struct {]
-        f.puts %Q[  void (*init)(mrb_state*);]
-        f.puts %Q[  void (*final)(mrb_state*);]
-        f.puts %Q[} gem_funcs[] = {]
-        f.write gem_funcs
-        f.puts %Q[};]
-        f.puts %Q[]
-        f.puts %Q[#define NUM_GEMS ((int)(sizeof(gem_funcs) / sizeof(gem_funcs[0])))]
-        f.puts %Q[]
-        f.puts %Q[struct final_mrbgems {]
-        f.puts %Q[  int i;]
-        f.puts %Q[  int ai;]
-        f.puts %Q[};]
-        f.puts %Q[]
-        f.puts %Q[static mrb_value]
-        f.puts %Q[final_mrbgems_body(mrb_state *mrb, void *ud) {]
-        f.puts %Q[  struct final_mrbgems *p = (struct final_mrbgems*)ud;]
-        f.puts %Q[  for (; p->i >= 0; p->i--) {]
-        f.puts %Q[    gem_funcs[p->i].final(mrb);]
-        f.puts %Q[    mrb_gc_arena_restore(mrb, p->ai);]
-        f.puts %Q[  }]
-        f.puts %Q[  return mrb_nil_value();]
-        f.puts %Q[}]
-        f.puts %Q[]
-        f.puts %Q[static void]
-        f.puts %Q[mrb_final_mrbgems(mrb_state *mrb) {]
-        f.puts %Q[  struct final_mrbgems a = { NUM_GEMS - 1, mrb_gc_arena_save(mrb) };]
-        f.puts %Q[  for (; a.i >= 0; a.i--) {]
-        f.puts %Q[    mrb_protect_error(mrb, final_mrbgems_body, &a, NULL);]
-        f.puts %Q[    mrb_gc_arena_restore(mrb, a.ai);]
-        f.puts %Q[  }]
-        f.puts %Q[}]
-        f.puts %Q[]
+        unless gem_funcs.empty?
+          f.write gem_func_decls
+          f.puts %Q[]
+          f.puts %Q[static const struct {]
+          f.puts %Q[  void (*init)(mrb_state*);]
+          f.puts %Q[  void (*final)(mrb_state*);]
+          f.puts %Q[} gem_funcs[] = {]
+          f.write gem_funcs
+          f.puts %Q[};]
+          f.puts %Q[]
+          f.puts %Q[#define NUM_GEMS ((int)(sizeof(gem_funcs) / sizeof(gem_funcs[0])))]
+          f.puts %Q[]
+          f.puts %Q[struct final_mrbgems {]
+          f.puts %Q[  int i;]
+          f.puts %Q[  int ai;]
+          f.puts %Q[};]
+          f.puts %Q[]
+          f.puts %Q[static mrb_value]
+          f.puts %Q[final_mrbgems_body(mrb_state *mrb, void *ud) {]
+          f.puts %Q[  struct final_mrbgems *p = (struct final_mrbgems*)ud;]
+          f.puts %Q[  for (; p->i >= 0; p->i--) {]
+          f.puts %Q[    gem_funcs[p->i].final(mrb);]
+          f.puts %Q[    mrb_gc_arena_restore(mrb, p->ai);]
+          f.puts %Q[  }]
+          f.puts %Q[  return mrb_nil_value();]
+          f.puts %Q[}]
+          f.puts %Q[]
+          f.puts %Q[static void]
+          f.puts %Q[mrb_final_mrbgems(mrb_state *mrb) {]
+          f.puts %Q[  struct final_mrbgems a = { NUM_GEMS - 1, mrb_gc_arena_save(mrb) };]
+          f.puts %Q[  for (; a.i >= 0; a.i--) {]
+          f.puts %Q[    mrb_protect_error(mrb, final_mrbgems_body, &a, NULL);]
+          f.puts %Q[    mrb_gc_arena_restore(mrb, a.ai);]
+          f.puts %Q[  }]
+          f.puts %Q[}]
+          f.puts %Q[]
+        end
         f.puts %Q[void]
         f.puts %Q[mrb_init_mrbgems(mrb_state *mrb) {]
-        f.puts %Q[  int ai = mrb_gc_arena_save(mrb);]
-        f.puts %Q[  for (int i = 0; i < NUM_GEMS; i++) {]
-        f.puts %Q[    gem_funcs[i].init(mrb);]
-        f.puts %Q[    mrb_gc_arena_restore(mrb, ai);]
-        f.puts %Q[    mrb_vm_ci_env_clear(mrb, mrb->c->cibase);]
-        f.puts %Q[    if (mrb->exc) {]
-        f.puts %Q[      mrb_exc_raise(mrb, mrb_obj_value(mrb->exc));]
-        f.puts %Q[    }]
-        f.puts %Q[  }]
-        f.puts %Q[  mrb_state_atexit(mrb, mrb_final_mrbgems);]
+        unless gem_funcs.empty?
+          f.puts %Q[  int ai = mrb_gc_arena_save(mrb);]
+          f.puts %Q[  for (int i = 0; i < NUM_GEMS; i++) {]
+          f.puts %Q[    gem_funcs[i].init(mrb);]
+          f.puts %Q[    mrb_gc_arena_restore(mrb, ai);]
+          f.puts %Q[    mrb_vm_ci_env_clear(mrb, mrb->c->cibase);]
+          f.puts %Q[    if (mrb->exc) {]
+          f.puts %Q[      mrb_exc_raise(mrb, mrb_obj_value(mrb->exc));]
+          f.puts %Q[    }]
+          f.puts %Q[  }]
+          f.puts %Q[  mrb_state_atexit(mrb, mrb_final_mrbgems);]
+        end
         f.puts %Q[}]
       end
     end