The Rack test suite does not pass on TruffleRuby

[eregon]

See rack/rack#1579 and rack/rack#1568 (comment).
Found by @ioquatix

[eregon]

OK, one issue is:

ruby -e 's=StringIO.new; p s.external_encoding; s.binmode; p s.external_encoding'

gives

#<Encoding:UTF-8>
#<Encoding:ASCII-8BIT>

on MRI but

#<Encoding:UTF-8>
#<Encoding:UTF-8>

on TruffleRuby.

That's what causes both Rack::Lint#test_0005_notice error errors and Rack::Lint#test_0008_notice header errors to fail.

[ioquatix]

Is UTF-8 considered binary? I don't get it?

[eregon]

No it's not. It was a bug that StringIO#binmode didn't change the external encoding (and did nothing but return self):

truffleruby/lib/truffle/stringio.rb

Lines 201 to 203 in 9e0b046

	def binmode
	self
	end

[ioquatix]

Haha, that's actually pretty funny :p

[eregon]

Fixed in d5d3d07, waiting for a nightly to build, and then I'll make a PR to add truffleruby-head in rack's CI: rack/rack#1588