[DRE-maint] Bug#888135: ruby-lapack: FTBFS on ruby2.5: `dirname': no implicit conversion of nil into String

[Chris West (Faux)]

Source: ruby-lapack
Version: 1.7.2-1
Severity: important
User: debian-ruby at lists.debian.org
Usertags: ruby2.5

Dear Maintainer,

This package fails to build against ruby2.5. Soon, there will
be a transition to ruby2.5, and this package will FTBFS in sid.

There may be some details on the wiki about common problems:
https://wiki.debian.org/Teams/Ruby/Ruby25Transition

Build log excerpt:

┌──────────────────────────────────────────────────────────────────────────────┐
│ Build native extensions for ruby2.5                                          │
└──────────────────────────────────────────────────────────────────────────────┘

/usr/bin/ruby2.5 /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb /build/ruby-lapack-1.7.2 debian/ruby-lapack
"make clean"
make[1]: Entering directory '/build/ruby-lapack-1.7.2/ext'
make[1]: Leaving directory '/build/ruby-lapack-1.7.2/ext'
"make clean"
make[1]: Entering directory '/build/ruby-lapack-1.7.2/ext'
make[1]: Leaving directory '/build/ruby-lapack-1.7.2/ext'
current directory: /build/ruby-lapack-1.7.2/ext
/usr/bin/ruby2.5 -r ./siteconf20180123-6749-8r2khb.rb extconf.rb
checking for -llapack... yes
extconf.rb:81:in `dirname': no implicit conversion of nil into String (TypeError)
	from extconf.rb:81:in `<main>'
~~~~~~~~~~~~~~~~~~~~~ ↓ mkmf.log ~~~~~~~~~~~~~~~~~~~~~
find_library: checking for -llapack... -------------------- yes

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.5.0 -I/usr/include/ruby-2.5.0/ruby/backward -I/usr/include/ruby-2.5.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fdebug-prefix-map=/build/ruby2.5-ed5dT1/ruby2.5-2.5.0=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.5  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.5.0 -I/usr/include/ruby-2.5.0/ruby/backward -I/usr/include/ruby-2.5.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fdebug-prefix-map=/build/ruby2.5-ed5dT1/ruby2.5-2.5.0=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.5 -llapack  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: 
14: int t(void) { ; return 0; }
/* end */

--------------------

/usr/lib/ruby/2.5.0/rubygems/ext/builder.rb:92:in `run': extconf failed, exit code 1 (Gem::InstallError)
	from /usr/lib/ruby/2.5.0/rubygems/ext/ext_conf_builder.rb:46:in `block in build'
	from /usr/lib/ruby/2.5.0/tempfile.rb:295:in `open'
	from /usr/lib/ruby/2.5.0/rubygems/ext/ext_conf_builder.rb:30:in `build'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:76:in `block in build_and_install'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:70:in `chdir'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:70:in `build_and_install'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:108:in `block in build_all_extensions'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:105:in `each'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:105:in `build_all_extensions'
	from /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb:121:in `<main>'
~~~~~~~~~~~~~~~~~~~~~ ↑ mkmf.log ~~~~~~~~~~~~~~~~~~~~~
/usr/lib/ruby/vendor_ruby/gem2deb.rb:56:in `run': /usr/bin/ruby2.5 /usr/lib/ruby/vendor_ruby/gem2deb/extension_builder.rb /build/ruby-lapack-1.7.2 debian/ruby-lapack (Gem2Deb::CommandFailed)
	from /usr/lib/ruby/vendor_ruby/gem2deb.rb:67:in `run_ruby'
	from /usr/lib/ruby/vendor_ruby/gem2deb/installer.rb:37:in `block in install_files_and_build_extensions'
	from /usr/lib/ruby/vendor_ruby/gem2deb/installer.rb:34:in `each'
	from /usr/lib/ruby/vendor_ruby/gem2deb/installer.rb:34:in `install_files_and_build_extensions'
	from /usr/lib/ruby/vendor_ruby/gem2deb/dh_ruby.rb:84:in `block in install'
	from /usr/lib/ruby/vendor_ruby/gem2deb/dh_ruby.rb:82:in `each'
	from /usr/lib/ruby/vendor_ruby/gem2deb/dh_ruby.rb:82:in `install'
	from /usr/bin/dh_ruby:94:in `<main>'
dh_auto_install: dh_ruby --install /build/ruby-lapack-1.7.2/debian/tmp returned exit code 1
make: *** [binary] Error 1
debian/rules:4: recipe for target 'binary' failed
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2

Full build log:
https://rbuild.fau.xxx/2018-01-23/ruby-lapack.log

Please fix it!

Cheers,
Chris.