[ruby/rubygems] Make the Bundler logger thread safe:

- The Logger is not thread safe when calling `with_level`.
  This now becomes problematic because we are using multiple
  threads during the resolution phase in order to fetch git gems.

https://github.com/ruby/rubygems/commit/380653ae74

lib/bundler/ui/shell.rb

@@ -17,6 +17,7 @@ module Bundler
         @level = ENV["DEBUG"] ? "debug" : "info"
         @warning_history = []
         @output_stream = :stdout
+        @thread_safe_logger_key = "logger_level_#{object_id}"
       end
 
       def add_color(string, *color)
@@ -97,11 +98,13 @@ module Bundler
       end
 
       def level(name = nil)
-        return @level unless name
+        current_level = Thread.current.thread_variable_get(@thread_safe_logger_key) || @level
+        return current_level unless name
+
         unless index = LEVELS.index(name)
           raise "#{name.inspect} is not a valid level"
         end
-        index <= LEVELS.index(@level)
+        index <= LEVELS.index(current_level)
       end
 
       def output_stream=(symbol)
@@ -167,12 +170,13 @@ module Bundler
         end * "\n"
       end
 
-      def with_level(level)
-        original = @level
-        @level = level
+      def with_level(desired_level)
+        old_level = level
+        Thread.current.thread_variable_set(@thread_safe_logger_key, desired_level)
+
         yield
       ensure
-        @level = original
+        Thread.current.thread_variable_set(@thread_safe_logger_key, old_level)
       end
 
       def with_output_stream(symbol)

spec/bundler/bundler/ui/shell_spec.rb

@@ -81,4 +81,32 @@ RSpec.describe Bundler::UI::Shell do
       end
     end
   end
+
+  describe "threads" do
+    it "is thread safe when using with_level" do
+      stop_thr1 = false
+      stop_thr2 = false
+
+      expect(subject.level).to eq("debug")
+
+      thr1 = Thread.new do
+        subject.silence do
+          sleep(0.1) until stop_thr1
+        end
+
+        stop_thr2 = true
+      end
+
+      thr2 = Thread.new do
+        subject.silence do
+          stop_thr1 = true
+          sleep(0.1) until stop_thr2
+        end
+      end
+
+      [thr1, thr2].each(&:join)
+
+      expect(subject.level).to eq("debug")
+    end
+  end
 end