[rubygems/rubygems] Emit progress to stderr when --parseable is passed to bundle outdated

Before, `bundle outdated --parseable` (or `--porcelain`) caused output
to be completely silenced during definition resolution, so nothing was
printed at all until the table of outdated gems was printed.

With this change, `--parseable`/`--porcelain` now prints progress to
stderr during resolution. E.g.:

```
Fetching gem metadata from https://rubygems.org/.........
Resolving dependencies...
```

This provides a better user experience, especially when
`outdated --parseable` takes several seconds or more.

The report of outdated gems is still printed to stdout, and the exit
status codes are unchanged, so the fundamental contract with other tools
consuming the `outdated --parseable` result should not be affected.

https://github.com/rubygems/rubygems/commit/7d4bb43570

lib/bundler/cli/outdated.rb

@@ -54,7 +54,7 @@ module Bundler
       end
 
       if options[:parseable]
-        Bundler.ui.silence(&definition_resolution)
+        Bundler.ui.progress(&definition_resolution)
       else
         definition_resolution.call
       end

lib/bundler/ui/shell.rb

@@ -119,6 +119,10 @@ module Bundler
         with_level("silent", &blk)
       end
 
+      def progress(&blk)
+        with_output_stream(:stderr, &blk)
+      end
+
       def unprinted_warnings
         []
       end
@@ -170,6 +174,14 @@ module Bundler
       ensure
         @level = original
       end
+
+      def with_output_stream(symbol)
+        original = output_stream
+        self.output_stream = symbol
+        yield
+      ensure
+        @output_stream = original
+      end
     end
   end
 end

lib/bundler/ui/silent.rb

@@ -84,6 +84,10 @@ module Bundler
         yield
       end
 
+      def progress
+        yield
+      end
+
       def unprinted_warnings
         @warnings
       end

spec/bundler/commands/outdated_spec.rb

@@ -438,19 +438,40 @@ RSpec.describe "bundle outdated" do
         G
       end
 
-      it "outputs a sorted list of outdated gems with a more minimal format" do
+      it "outputs a sorted list of outdated gems with a more minimal format to stdout" do
         minimal_output = "activesupport (newest 3.0, installed 2.3.5, requested = 2.3.5)\n" \
                          "weakling (newest 0.2, installed 0.0.3, requested ~> 0.0.1)"
         subject
         expect(out).to eq(minimal_output)
       end
+
+      it "outputs progress to stderr" do
+        subject
+        expect(err).to include("Fetching gem metadata")
+      end
     end
 
     context "and no gems are outdated" do
-      it "has empty output" do
+      before do
+        build_repo2 do
+          build_gem "activesupport", "3.0"
+        end
+
+        install_gemfile <<-G
+          source "https://gem.repo2"
+          gem "activesupport", "3.0"
+        G
+      end
+
+      it "does not output to stdout" do
         subject
         expect(out).to be_empty
       end
+
+      it "outputs progress to stderr" do
+        subject
+        expect(err).to include("Fetching gem metadata")
+      end
     end
   end