Added `experimental` warning category

[Feature #16420]

error.c

@@ -144,6 +144,9 @@ rb_warning_category_from_name(VALUE category)
     if (category == ID2SYM(rb_intern("deprecated"))) {
         cat = RB_WARN_CATEGORY_DEPRECATED;
     }
+    else if (category == ID2SYM(rb_intern("experimental"))) {
+        cat = RB_WARN_CATEGORY_EXPERIMENTAL;
+    }
     else {
         rb_raise(rb_eArgError, "unknown category: %"PRIsVALUE, category);
     }

internal.h

@@ -1558,6 +1558,7 @@ PRINTF_ARGS(void rb_syserr_enc_warning(int err, rb_encoding *enc, const char *fm
 typedef enum {
     RB_WARN_CATEGORY_NONE,
     RB_WARN_CATEGORY_DEPRECATED,
+    RB_WARN_CATEGORY_EXPERIMENTAL,
 } rb_warning_category_t;
 rb_warning_category_t rb_warning_category_from_name(VALUE category);
 bool rb_warning_category_enabled_p(rb_warning_category_t category);

parse.y

@@ -11457,7 +11457,8 @@ new_case3(struct parser_params *p, NODE *val, NODE *pat, const YYLTYPE *loc)
 {
     NODE *node = NEW_CASE3(val, pat, loc);
 
-    rb_warn0L(nd_line(node), "Pattern matching is experimental, and the behavior may change in future versions of Ruby!");
+    if (rb_warning_category_enabled_p(RB_WARN_CATEGORY_EXPERIMENTAL))
+	rb_warn0L(nd_line(node), "Pattern matching is experimental, and the behavior may change in future versions of Ruby!");
     return node;
 }
 

test/ruby/test_exception.rb

@@ -1266,6 +1266,7 @@ $stderr = $stdout; raise "\x82\xa0"') do |outs, errs, status|
     assert_raise(TypeError) {Warning[nil]}
     assert_raise(ArgumentError) {Warning[:XXXX]}
     assert_include([true, false], Warning[:deprecated])
+    assert_include([true, false], Warning[:experimental])
   end
 
   def test_undefined_backtrace

test/ruby/test_pattern_matching.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require 'test/unit'
 
-verbose, $VERBOSE = $VERBOSE, nil # suppress "warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!"
+experimental, Warning[:experimental] = Warning[:experimental], false # suppress "warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!"
 eval "\n#{<<~'END_of_GUARD'}", binding, __FILE__, __LINE__
 class TestPatternMatching < Test::Unit::TestCase
   class C
@@ -92,7 +92,8 @@ class TestPatternMatching < Test::Unit::TestCase
     end
 
     assert_block do
-      verbose, $VERBOSE = $VERBOSE, nil # suppress "warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!"
+      # suppress "warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!"
+      experimental, Warning[:experimental] = Warning[:experimental], false
       eval(%q{
         case true
         in a
@@ -100,7 +101,7 @@ class TestPatternMatching < Test::Unit::TestCase
         end
       })
     ensure
-      $VERBOSE = verbose
+      Warning[:experimental] = experimental
     end
 
     assert_block do
@@ -1274,6 +1275,23 @@ END
       1 in a:
     }, /unexpected/, '[ruby-core:95098]')
   end
+
+  def assert_experimental_warning(code)
+    w = Warning[:experimental]
+
+    Warning[:experimental] = false
+    assert_warn('') {eval(code)}
+
+    Warning[:experimental] = true
+    assert_warn(/Pattern matching is experimental/) {eval(code)}
+  ensure
+    Warning[:experimental] = w
+  end
+
+  def test_experimental_warning
+    assert_experimental_warning("case 0; in 0; end")
+    assert_experimental_warning("0 in 0")
+  end
 end
 END_of_GUARD
-$VERBOSE = verbose
+Warning[:experimental] = experimental