From c53aec73ddf94bb9a06bead62c3bf58c5ba49bd3 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Tue, 19 Nov 2019 15:06:11 +0900
Subject: Configure static extensions only if in charge

Get rid of races in parallel configuration when using the
ext/Setup file.
---
 ext/extmk.rb | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/ext/extmk.rb b/ext/extmk.rb
index 6045750fd2..80a0a1208d 100755
--- a/ext/extmk.rb
+++ b/ext/extmk.rb
@@ -463,7 +463,11 @@ end unless $extstatic
 if ARGV[0]
   ext_prefix, exts = ARGV.shift.split('/', 2)
   $extension = [exts] if exts
-  @gemname = exts if ext_prefix == 'gems'
+  if ext_prefix == 'gems'
+    @gemname = exts
+  elsif exts
+    $static_ext.delete_if {|t, *| !File.fnmatch(t, exts)}
+  end
 end
 ext_prefix = "#{$top_srcdir}/#{ext_prefix || 'ext'}"
 exts = $static_ext.sort_by {|t, i| i}.collect {|t, i| t}
-- 
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