skylight: lib/mri/mkmf.rb:1299:in `find_type': wrong number of arguments (given 1, expected 2+) (ArgumentError)

[deepj]

To reproduce:

gem install skylight

Error:

ERROR:  Error installing skylight:
	ERROR: Failed to build gem native extension.

    current directory: ~/.gem/truffleruby/2.6.5/gems/skylight-4.2.1/ext
~/.rubies/truffleruby-20.1.0-dev/bin/truffleruby -I ~/.rubies/truffleruby-20.1.0-dev/lib/mri -r ./siteconf20200208-39800-1h6f77a.rb extconf.rb
~/.rubies/truffleruby-20.1.0-dev/lib/mri/mkmf.rb:1299:in `find_type': wrong number of arguments (given 1, expected 2+) (ArgumentError)
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/ffi/struct.rb:272:in `find_type'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/ffi/struct.rb:266:in `find_field_type'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/ffi/struct.rb:306:in `array_layout'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/ffi/struct.rb:218:in `layout'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle.rb:63:in `config'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle/foreign/addrinfo.rb:31:in `Addrinfo'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle/foreign/addrinfo.rb:30:in `Foreign'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle/foreign/addrinfo.rb:29:in `Socket'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle/foreign/addrinfo.rb:28:in `Truffle'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket/truffle/foreign/addrinfo.rb:27:in `<top (required)>'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/truffle/socket.rb:38:in `<top (required)>'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/net/protocol.rb:22:in `<top (required)>'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/net/http.rb:23:in `require_relative'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/net/http.rb:23:in `<top (required)>'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.gem/truffleruby/2.6.5/gems/skylight-4.2.1/lib/skylight/native_ext_fetcher.rb:3:in `<top (required)>'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from ~/.rubies/truffleruby-20.1.0-dev/lib/mri/rubygems/core_ext/kernel_require.rb:54:in `require'
	from extconf.rb:9:in `<main>'
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=~/.rubies/truffleruby-20.1.0-dev/bin/truffleruby
log file does not exist

extconf failed, exit code 1

Gem files will remain installed in ~/.gem/truffleruby/2.6.5/gems/skylight-4.2.1 for inspection.
Results logged to ~/.gem/truffleruby/2.6.5/extensions/x86_64-darwin/20.1.0-dev-9e0b0468/skylight-4.2.1/gem_make.out

[eregon]

Interesting case where code in FFI ends up conflicting with code in mkmf.rb.
I'll need to find out why it doesn't happen on MRI.

[eregon]

ruby -rmkmf -rffi -e 'module A; class A < FFI::Struct; layout :a, :int; end; end'

reproduces and also fails in MRI.

So basically it's an issue of FFI: ffi/ffi#776
Because mkmf defines a public find_type on every object by include MakeMakefile.

The only reason it doesn't fail on MRI for the extconf.rb is that MRI doesn't use FFI internally for the socket stdlib.

The require chain here is extconf.rb -> net/http -> socket -> ffi and in #2010 it's extconf.rb -> openssl -> ipaddr -> socket -> ffi.

[eregon]

Fixed by a54e85b.
gem install skylight works for me locally now.