Fix Kernel.warn and don't call Warning#warn if a specified category is disabled

Author: andrykonchin

CHANGELOG.md

@@ -39,6 +39,7 @@ Compatibility:
 * Fix `Thread#{thread_variable_get,thread_variable_set,thread_variable?,key?,[],[]=,fetch}` and convert a non-String/Symbol thread-local variable name to String using `#to_str` (@andrykonchin).
 * Fix formatting in `Exception#full_message` when `RuntimeError` is not handled and `highlight` option is specified (@andrykonchin).
 * Fix `String#encode` and convert fallback values into String using `#to_str` (@andrykonchin).
+* Fix `Kernel.warn` and don't call `Warning#warn` if a specified category is disabled (@andrykonchin).
 
 Performance:
 

spec/ruby/core/warning/warn_spec.rb

@@ -121,7 +121,7 @@ def Warning.warn(msg)
     end
   end
 
-  ruby_bug '#19530', ''...'3.4' do
+  ruby_bug '#20573', ''...'3.4' do
     it "isn't called by Kernel.warn when category is :deprecated but Warning[:deprecated] is false" do
       warn_deprecated = Warning[:deprecated]
       begin

spec/tags/core/warning/warn_tags.txt

@@ -2,5 +2,3 @@ slow:Warning.warn has Warning as the method owner
 slow:Warning.warn can be overridden
 slow:Warning.warn does not add a newline
 slow:Warning.warn returns nil
-fails:Warning.warn isn't called by Kernel.warn when category is :deprecated but Warning[:deprecated] is false
-fails:Warning.warn isn't called by Kernel.warn when category is :experimental but Warning[:experimental] is false

src/main/ruby/truffleruby/core/kernel.rb

@@ -629,6 +629,12 @@ def untrace_var(name, cmd = undefined)
 
   def warn(*messages, uplevel: undefined, category: nil)
     if !Primitive.nil?($VERBOSE) && !messages.empty?
+      unless Primitive.nil?(category)
+        category = Truffle::Type.rb_convert_type(category, Symbol, :to_sym)
+        Truffle::WarningOperations.check_category(category)
+        return nil unless Warning[category]
+      end
+
       prefix = if Primitive.undefined?(uplevel)
                  ''
                else
@@ -662,15 +668,13 @@ def warn(*messages, uplevel: undefined, category: nil)
         unless message.encoding.ascii_compatible?
           raise Encoding::CompatibilityError, "ASCII incompatible encoding: #{message.encoding}"
         end
-        Truffle::WarningOperations.check_category(category) unless Primitive.nil?(category)
 
         $stderr.write message
       else
         warning_warn = Warning.method(:warn)
         if warning_warn.arity == 1
           warning_warn.call(message)
         else
-          category = Truffle::Type.rb_convert_type(category, Symbol, :to_sym) unless Primitive.nil?(category)
           warning_warn.call(message, category: category)
         end
       end