From 2901dae9484e5311e68517016ddfe57f257734df Mon Sep 17 00:00:00 2001
From: Brian Cain <bcain@hashicorp.com>
Date: Fri, 22 Nov 2019 12:04:09 -0800
Subject: [PATCH] Add option for docker executor to handle stderr from results

Instead of always joining stdout and stderr, only join the two if the
caller explicitly asks for it. Otherwise, only return stdout.
---
 plugins/providers/docker/driver.rb         |  7 ++++---
 plugins/providers/docker/executor/local.rb | 10 ++++++----
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/plugins/providers/docker/driver.rb b/plugins/providers/docker/driver.rb
index f2b382fc3..8932c74a2 100644
--- a/plugins/providers/docker/driver.rb
+++ b/plugins/providers/docker/driver.rb
@@ -20,9 +20,10 @@ module VagrantPlugins
       #
       # @return [String] id - ID matched from the docker build output.
       def build(dir, **opts, &block)
-        args   = Array(opts[:extra_args])
-        args   << dir
-        result = execute('docker', 'build', *args, &block)
+        args = Array(opts[:extra_args])
+        args << dir
+        opts = {with_stderr: true}
+        result = execute('docker', 'build', *args, opts, &block)
         matches = result.match(/Successfully built (?<id>.+)$/i)
         if !matches
           # Check for the new output format 'writing image sha256...'
diff --git a/plugins/providers/docker/executor/local.rb b/plugins/providers/docker/executor/local.rb
index f99c4f929..7825a0292 100644
--- a/plugins/providers/docker/executor/local.rb
+++ b/plugins/providers/docker/executor/local.rb
@@ -27,10 +27,12 @@ module VagrantPlugins
               stdout: result.stdout
           end
 
-          if result.stdout.to_s.strip.length == 0
-            result.stderr
-          else
-            result.stdout
+          if opts
+            if opts[:with_stderr]
+              return result.stdout + " " + result.stderr
+            else
+              return result.stdout
+            end
           end
         end