Auto merge of #5665 - bundler:colby/stderr-feature, r=indirect

Print errors to stderr

As we discussed, i'm going to start porting over features from the 2-0-dev branch into feature flags.

This PR adds the feature to print bundler errors to `stderr` instead of `stdout`. I had a look to see how feature flags worked and i think i have the idea down but let me know if i missed something.

Thanks!

\cc @segiddins @indirect

5 files changed, 62 insertions, 2 deletions

diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index 150cac1e67..5ee69f538c 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -17,6 +17,7 @@ module Bundler
     settings_flag(:allow_offline_install) { bundler_2_mode? }
     settings_flag(:only_update_to_newer_versions) { bundler_2_mode? }
     settings_flag(:plugins) { @bundler_version >= Gem::Version.new("1.14") }
+    settings_flag(:error_on_stderr) { bundler_2_mode? }
 
     def initialize(bundler_version)
       @bundler_version = Gem::Version.create(bundler_version)
diff --git a/lib/bundler/settings.rb b/lib/bundler/settings.rb
index 62c21a2ecb..9a93eebf83 100644
--- a/lib/bundler/settings.rb
+++ b/lib/bundler/settings.rb
@@ -27,6 +27,7 @@ module Bundler
       only_update_to_newer_versions
       plugins
       silence_root_warning
+      error_on_stderr
     ).freeze
 
     NUMBER_KEYS = %w(
diff --git a/lib/bundler/ui/shell.rb b/lib/bundler/ui/shell.rb
index 87a92471fb..5d4fd76acb 100644
--- a/lib/bundler/ui/shell.rb
+++ b/lib/bundler/ui/shell.rb
@@ -9,7 +9,7 @@ module Bundler
       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
@@ -36,7 +36,9 @@ module Bundler
       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 +105,11 @@ 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")
 
diff --git a/man/bundle-config.ronn b/man/bundle-config.ronn
index afae3e0888..b7ae07698c 100644
--- a/man/bundle-config.ronn
+++ b/man/bundle-config.ronn
@@ -222,6 +222,8 @@ learn more about their operation in [bundle install(1)][bundle-install].
 * `gem.push_key` (`BUNDLE_GEM__PUSH_KEY`):
    Sets the `--key` parameter for `gem push` when using the `rake release`
    command with a private gemstash server.
+* `error_on_stderr` (`BUNDLE_ERROR_ON_STDERR`)
+   Print Bundler errors to stderr
 
 In general, you should set these settings per-application by using the applicable
 flag to the [bundle install(1)][bundle-install] or [bundle package(1)][bundle-package] command.
diff --git a/spec/bundler/ui/shell_spec.rb b/spec/bundler/ui/shell_spec.rb
new file mode 100644
index 0000000000..c5ccce534a
--- /dev/null
+++ b/spec/bundler/ui/shell_spec.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+require "spec_helper"
+
+RSpec.describe Bundler::UI::Shell do
+  subject { described_class.new }
+
+  before { subject.level = "debug" }
+
+  describe "#info" do
+    before { subject.level = "info" }
+    it "prints to stdout" do
+      expect { subject.info("info") }.to output("info\n").to_stdout
+    end
+  end
+
+  describe "#confirm" do
+    before { subject.level = "confirm" }
+    it "prints to stdout" do
+      expect { subject.confirm("confirm") }.to output("confirm\n").to_stdout
+    end
+  end
+
+  describe "#warn" do
+    before { subject.level = "warn" }
+    it "prints to stdout" do
+      expect { subject.warn("warning") }.to output("warning\n").to_stdout
+    end
+  end
+
+  describe "#debug" do
+    it "prints to stdout" do
+      expect { subject.debug("debug") }.to output("debug\n").to_stdout
+    end
+  end
+
+  describe "#error" do
+    before { subject.level = "error" }
+    it "prints to stdout" do
+      expect { subject.error("error!!!") }.to output("error!!!\n").to_stdout
+    end
+
+    context "when stderr flag is enabled" do
+      before { Bundler.settings.temporary(:error_on_stderr => true) }
+      it "prints to stderr" do
+        expect { subject.error("error!!!") }.to output("error!!!\n").to_stderr
+      end
+    end
+  end
+end