From bd47c2a5998657ad07e610b9873c362b353371cf Mon Sep 17 00:00:00 2001
From: Benoit Daloze <eregontp@gmail.com>
Date: Thu, 3 Mar 2022 13:34:35 +0100
Subject: [PATCH] Add `--error-output stderr` option to only print
 errors/failures on stderr

* See https://github.com/ruby/ruby/pull/5510
  and https://github.com/ruby/ruby/pull/5487
---
 lib/mspec/commands/mspec.rb         |  6 ++++--
 lib/mspec/runner/formatters/base.rb | 18 +++++++++++++-----
 lib/mspec/utils/options.rb          | 11 ++++++++++-
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/lib/mspec/commands/mspec.rb b/lib/mspec/commands/mspec.rb
index 9d82949f..9c38cebc 100755
--- a/lib/mspec/commands/mspec.rb
+++ b/lib/mspec/commands/mspec.rb
@@ -25,6 +25,7 @@ def options(argv = ARGV)
     config[:command] = argv.shift if ["ci", "run", "tag"].include?(argv[0])
 
     options = MSpecOptions.new "mspec [COMMAND] [options] (FILE|DIRECTORY|GLOB)+", 30, config
+    @options = options
 
     options.doc " The mspec command sets up and invokes the sub-commands"
     options.doc " (see below) to enable, for instance, running the specs"
@@ -110,8 +111,9 @@ def run
     if config[:multi]
       exit multi_exec(argv)
     else
-      $stderr.puts "$ #{argv.join(' ')}"
-      $stderr.flush
+      log = config[:options].include?('--error-output') ? $stdout : $stderr
+      log.puts "$ #{argv.join(' ')}"
+      log.flush
       exec(*argv, close_others: false)
     end
   end
diff --git a/lib/mspec/runner/formatters/base.rb b/lib/mspec/runner/formatters/base.rb
index 6c075c4d..c7c50c40 100644
--- a/lib/mspec/runner/formatters/base.rb
+++ b/lib/mspec/runner/formatters/base.rb
@@ -1,6 +1,7 @@
 require 'mspec/expectations/expectations'
 require 'mspec/runner/actions/timer'
 require 'mspec/runner/actions/tally'
+require 'mspec/utils/options'
 
 if ENV['CHECK_LEAKS']
   require 'mspec/runner/actions/leakchecker'
@@ -18,10 +19,17 @@ def initialize(out = nil)
 
     @count = 0 # For subclasses
 
-    if out.nil?
+    if out
+      @out = File.open out, "w"
+    else
       @out = $stdout
+    end
+
+    err = MSpecOptions.latest && MSpecOptions.latest.config[:error_output]
+    if err
+      @err = (err == 'stderr') ? $stderr : File.open(err, "w")
     else
-      @out = File.open out, "w"
+      @err = @out
     end
   end
 
@@ -115,9 +123,9 @@ def finish
 
   def print_exception(exc, count)
     outcome = exc.failure? ? "FAILED" : "ERROR"
-    print "\n#{count})\n#{exc.description} #{outcome}\n"
-    print exc.message, "\n"
-    print exc.backtrace, "\n"
+    @err.print "\n#{count})\n#{exc.description} #{outcome}\n"
+    @err.print exc.message, "\n"
+    @err.print exc.backtrace, "\n"
   end
 
   # A convenience method to allow printing to different outputs.
diff --git a/lib/mspec/utils/options.rb b/lib/mspec/utils/options.rb
index bef1dbdd..23a4c9a2 100644
--- a/lib/mspec/utils/options.rb
+++ b/lib/mspec/utils/options.rb
@@ -32,6 +32,10 @@ class OptionError < Exception; end
   # Raised if an unrecognized option is encountered.
   class ParseError < Exception; end
 
+  class << self
+    attr_accessor :latest
+  end
+
   attr_accessor :config, :banner, :width, :options
 
   def initialize(banner = "", width = 30, config = nil)
@@ -46,7 +50,7 @@ def initialize(banner = "", width = 30, config = nil)
       @extra << x
     }
 
-    yield self if block_given?
+    MSpecOptions.latest = self
   end
 
   # Registers an option. Acceptable formats for arguments are:
@@ -311,6 +315,11 @@ def formatters
        "Write formatter output to FILE") do |f|
       config[:output] = f
     end
+
+    on("--error-output", "FILE",
+       "Write error output of failing specs to FILE, or $stderr if value is 'stderr'.") do |f|
+      config[:error_output] = f
+    end
   end
 
   def filters