Show experimental warning when namespace is enabled

common.mk

@@ -11041,6 +11041,7 @@ namespace.$(OBJEXT): $(top_srcdir)/internal/array.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/basic_operators.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/class.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/compilers.h
+namespace.$(OBJEXT): $(top_srcdir)/internal/error.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/eval.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/file.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/gc.h
@@ -11053,6 +11054,7 @@ namespace.$(OBJEXT): $(top_srcdir)/internal/serial.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/set_table.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/st.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/static_assert.h
+namespace.$(OBJEXT): $(top_srcdir)/internal/string.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/variable.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/vm.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/warnings.h

doc/namespace.md

@@ -0,0 +1,16 @@
+# Namespace - Ruby's in-process separation of Classes and Modules
+
+Namespace is designed to provide separated spaces in a Ruby process, to isolate applications and libraries.
+
+## Known issues
+
+* Experimental warning is shown when ruby starts with `RUBY_NAMESPACE=1` (specify `-W:no-experimental` command line option to hide it)
+
+## TODOs
+
+## How to use
+
+## Summary
+
+## Specs
+

internal/namespace.h

@@ -4,12 +4,12 @@
 #include "ruby/ruby.h"          /* for VALUE */
 
 /**
- * @author     Satoshi Tagomori <tagomoris@gmail.com>
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
  * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
  *             Permission  is hereby  granted,  to  either redistribute  and/or
  *             modify this file, provided that  the conditions mentioned in the
  *             file COPYING are met.  Consult the file for details.
- * @brief      Internal header for Fiber.
+ * @brief      Internal header for Namespace.
  */
 struct rb_namespace_struct {
     /*

namespace.c

@@ -3,6 +3,7 @@
 #include "internal.h"
 #include "internal/class.h"
 #include "internal/eval.h"
+#include "internal/error.h"
 #include "internal/file.h"
 #include "internal/gc.h"
 #include "internal/hash.h"
@@ -960,6 +961,8 @@ rb_namespace_require_relative(VALUE namespace, VALUE fname)
     return rb_ensure(rb_require_relative_entrypoint, fname, namespace_both_pop, (VALUE)&arg);
 }
 
+static int namespace_experimental_warned = 0;
+
 void
 rb_initialize_main_namespace(void)
 {
@@ -968,6 +971,13 @@ rb_initialize_main_namespace(void)
     rb_thread_t *th = GET_THREAD();
     VALUE main_ns;
 
+    if (!namespace_experimental_warned) {
+        rb_category_warn(RB_WARN_CATEGORY_EXPERIMENTAL,
+                         "Namespace is experimental, and the behavior may change in the future!\n"
+                         "See doc/namespace.md for know issues, etc.");
+        namespace_experimental_warned = 1;
+    }
+
     main_ns = rb_class_new_instance_pass_kw(0, NULL, rb_cNamespace);
     ns = rb_get_namespace_t(main_ns);
     ns->ns_object = main_ns;