Match `--with/--without` options against gem names

The simple names in `default_exclude_exts` do not match extension
paths under gems.

Extract each gem name from the gemspec file at the top level of each
gem directory.  For example, if `ext` is `syslog-0.1.2/ext/syslog/`,
find out `syslog-0.1.2/syslog.gemspec` and take the base name `syslog`
without the suffix `.gemspec`.

1 files changed, 6 insertions, 0 deletions

diff --git a/ext/extmk.rb b/ext/extmk.rb
index ffd64209ae..6c7c7aeab7 100755
--- a/ext/extmk.rb
+++ b/ext/extmk.rb
@@ -517,6 +517,12 @@ cond = proc {|ext, *|
   incl, excl = Dir.glob("#{e}/**/extconf.rb", base: "#$top_srcdir/#{ext_prefix}").collect {|d|
     File.dirname(d)
   }.partition {|ext|
+    if @gemname
+      ext = ext[%r[\A[^/]+]] # extract gem name
+      Dir.glob("*.gemspec", base: "#$top_srcdir/#{ext_prefix}/#{ext}") do |g|
+        break ext = g if ext.start_with?("#{g.chomp!(".gemspec")}-")
+      end
+    end
     with_config(ext, &cond)
   }
   incl.sort!