[ruby/prism] Warn when the parser translator receives an incompatible builder class

In https://github.com/ruby/prism/pull/3494 I added a bit of code
so that using the new builder doesn't break stuff.
This code can be dropped when it is enforced that builder
is _always_ the correct subclass (and makes future issues like that unlikely).

https://github.com/ruby/prism/commit/193d4b806d

lib/prism/translation/parser.rb

@@ -59,6 +59,12 @@ module Prism
       # should be implemented as needed.
       #
       def initialize(builder = Prism::Translation::Parser::Builder.new, parser: Prism)
+        if !builder.is_a?(Prism::Translation::Parser::Builder)
+          warn(<<~MSG, uplevel: 1)
+            [deprecation]: The builder passed to `Prism::Translation::Parser.new` is not a \
+            `Prism::Translation::Parser::Builder` subclass. This will raise in the next major version.
+          MSG
+        end
         @parser = parser
 
         super(builder)

test/prism/ruby/parser_test.rb

@@ -145,6 +145,16 @@ module Prism
       end
     end
 
+    def test_non_prism_builder_class_deprecated
+      warnings = capture_warnings { Prism::Translation::Parser33.new(Parser::Builders::Default.new) }
+
+      assert_include(warnings, "#{__FILE__}:#{__LINE__ - 2}")
+      assert_include(warnings, "is not a `Prism::Translation::Parser::Builder` subclass")
+
+      warnings = capture_warnings { Prism::Translation::Parser33.new }
+      assert_empty(warnings)
+    end
+
     def test_it_block_parameter_syntax
       it_fixture_path = Pathname(__dir__).join("../../../test/prism/fixtures/it.txt")
 

test/prism/test_helper.rb

@@ -314,15 +314,16 @@ module Prism
       end
     end
 
-    def ignore_warnings
-      previous = $VERBOSE
-      $VERBOSE = nil
+    def capture_warnings
+      $stderr = StringIO.new
+      yield
+      $stderr.string
+    ensure
+      $stderr = STDERR
+    end
 
-      begin
-        yield
-      ensure
-        $VERBOSE = previous
-      end
+    def ignore_warnings
+      capture_warnings { return yield }
     end
   end
 end