1 files changed, 15 insertions, 4 deletions
diff --git a/lib/bundler/ui/shell.rb b/lib/bundler/ui/shell.rb
index 87a92471fb..3b3b6bfb53 100644
--- a/lib/bundler/ui/shell.rb
+++ b/lib/bundler/ui/shell.rb
@@ -1,15 +1,16 @@
 # frozen_string_literal: true
+
 require "bundler/vendored_thor"
 
 module Bundler
   module UI
     class Shell
-      LEVELS = %w(silent error warn confirm info debug).freeze
+      LEVELS = %w[silent error warn confirm info debug].freeze
 
       attr_writer :shell
 
       def initialize(options = {})
-        if options["no-color"] || !STDOUT.tty?
+        if options["no-color"] || !$stdout.tty?
           Thor::Base.shell = Thor::Shell::Basic
         end
         @shell = Thor::Base.shell.new
@@ -30,13 +31,18 @@ module Bundler
       end
 
       def warn(msg, newline = nil)
+        return unless level("warn")
         return if @warning_history.include? msg
         @warning_history << msg
-        tell_me(msg, :yellow, newline) if level("warn")
+
+        return tell_err(msg, :yellow, newline) if Bundler.feature_flag.error_on_stderr?
+        tell_me(msg, :yellow, newline)
       end
 
       def error(msg, newline = nil)
-        tell_me(msg, :red, newline) if level("error")
+        return unless level("error")
+        return tell_err(msg, :red, newline) if Bundler.feature_flag.error_on_stderr?
+        tell_me(msg, :red, newline)
       end
 
       def debug(msg, newline = nil)
@@ -103,6 +109,11 @@ module Bundler
       end
 
       def tell_err(message, color = nil, newline = nil)
+        newline = message.to_s !~ /( |\t)\Z/ unless newline
+        message = word_wrap(message) if newline.is_a?(Hash) && newline[:wrap]
+
+        color = nil if color && !$stderr.tty?
+
         buffer = @shell.send(:prepare_message, message, *color)
         buffer << "\n" if newline && !message.to_s.end_with?("\n")