Fix another silent rubygems issue

We might be shelling out to rubygems in a `bundle exec` context. In the
case where we don't shell out to the `gem` binstub directly, the
previous trick wouldn't work.

Instead, reset the rubygems ui right after `bundler/setup`, so that if
we end up shelling out to rubygems, it will use its default shell
(non-silent).

The best place to fix this would probably be right inside the `gem`
script, but even if we fix it there, we'll need workarounds for previous
rubygems versions inside `bundler` so I think this is good for now.

lib/bundler/cli/exec.rb

@@ -25,12 +25,12 @@ def run
       SharedHelpers.set_bundle_environment
       if bin_path = Bundler.which(cmd)
         if !Bundler.settings[:disable_exec_load] && ruby_shebang?(bin_path)
-          return with_verbose_rubygems { kernel_load(bin_path, *args) }
+          return kernel_load(bin_path, *args)
         end
-        with_verbose_rubygems { kernel_exec(bin_path, *args) }
+        kernel_exec(bin_path, *args)
       else
         # exec using the given command
-        with_verbose_rubygems { kernel_exec(cmd, *args) }
+        kernel_exec(cmd, *args)
       end
     end
 
@@ -89,14 +89,5 @@ def ruby_shebang?(file)
       first_line = File.open(file, "rb") {|f| f.read(possibilities.map(&:size).max) }
       possibilities.any? {|shebang| first_line.start_with?(shebang) }
     end
-
-    def with_verbose_rubygems
-      old_ui = Gem::DefaultUserInteraction.ui
-      Gem::DefaultUserInteraction.ui = nil
-
-      yield
-    ensure
-      Gem::DefaultUserInteraction.ui = old_ui
-    end
   end
 end

lib/bundler/setup.rb

@@ -19,4 +19,9 @@
   else
     Bundler.ui.silence { Bundler.setup }
   end
+
+  # We might be in the middle of shelling out to rubygems
+  # (RUBYOPT=-rbundler/setup), so we need to give rubygems the opportunity of
+  # not being silent.
+  Gem::DefaultUserInteraction.ui = nil
 end

spec/commands/exec_spec.rb

@@ -61,6 +61,12 @@
     expect(out).to eq(Gem::VERSION)
   end
 
+  it "works when exec'ing to rubygems through sh -c" do
+    install_gemfile 'gem "rack"'
+    bundle "exec sh -c '#{gem_cmd} --version'"
+    expect(out).to eq(Gem::VERSION)
+  end
+
   it "respects custom process title when loading through ruby" do
     script_that_changes_its_own_title_and_checks_if_picked_up_by_ps_unix_utility = <<~'RUBY'
       Process.setproctitle("1-2-3-4-5-6-7-8-9-10-11-12-13-14-15")