simdjson: ISO C++17 does not allow 'register' storage class specifier simdjson

[deepj]

truffleruby 20.1.0-dev-08311e22, like ruby 2.6.5, GraalVM CE Native [x86_64-darwin]

To reproduce:

$ gem install simdjson

Error:

Fetching simdjson-0.2.0.gem
Building native extensions. This could take a while...
ERROR:  Error installing simdjson:
	ERROR: Failed to build gem native extension.

    current directory: ~/.gem/truffleruby/2.6.5/gems/simdjson-0.2.0/ext/simdjson
~/.rubies/truffleruby-dev/bin/truffleruby -I ~/.rubies/truffleruby-dev/lib/mri -r ./siteconf20200224-84741-1hdzy5a.rb extconf.rb
creating Makefile

current directory: ~/.gem/truffleruby/2.6.5/gems/simdjson-0.2.0/ext/simdjson
make "DESTDIR=" clean

current directory: ~/.gem/truffleruby/2.6.5/gems/simdjson-0.2.0/ext/simdjson
make "DESTDIR="
compiling simdjson.cpp
In file included from simdjson.cpp:5:
In file included from ./simdjson.hpp:4:
In file included from ~/.rubies/truffleruby-dev/lib/cext/include/ruby.h:33:
~/.rubies/truffleruby-dev/lib/cext/include/ruby/ruby.h:902:1: warning: empty struct has size 0 in C, size 1 in C++ [-Wextern-c-compat]
struct RUBY_ALIGNAS(SIZEOF_VALUE) RBasic {
^
In file included from simdjson.cpp:5:
In file included from ./simdjson.hpp:4:
In file included from ~/.rubies/truffleruby-dev/lib/cext/include/ruby.h:33:
In file included from ~/.rubies/truffleruby-dev/lib/cext/include/ruby/ruby.h:1939:
~/.rubies/truffleruby-dev/lib/cext/include/ruby/intern.h:56:19: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
void rb_mem_clear(register VALUE*, register long);
                  ^~~~~~~~~
~/.rubies/truffleruby-dev/lib/cext/include/ruby/intern.h:56:36: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
void rb_mem_clear(register VALUE*, register long);
                                   ^~~~~~~~~
1 warning and 2 errors generated.
make: *** [simdjson.o] Error 1

make failed, exit code 2

Gem files will remain installed in ~/.gem/truffleruby/2.6.5/gems/simdjson-0.2.0 for inspection.
Results logged to ~/.gem/truffleruby/2.6.5/extensions/x86_64-darwin/20.1.0-dev-08311e22/simdjson-0.2.0/gem_make.out

[eregon]

The same warning happens on MRI 2.6.5 too with gcc, except there it's a warning and not an error:

compiling simdjson.cpp
cc1plus: warning: command line option ‘-Wdeclaration-after-statement’ is valid for C/ObjC but not for C++
cc1plus: warning: command line option ‘-Wimplicit-function-declaration’ is valid for C/ObjC but not for C++
cc1plus: warning: command line option ‘-Wimplicit-int’ is valid for C/ObjC but not for C++
In file included from /home/eregon/.rubies/ruby-2.6.5/include/ruby-2.6.0/ruby/ruby.h:2111,
                 from /home/eregon/.rubies/ruby-2.6.5/include/ruby-2.6.0/ruby.h:33,
                 from simdjson.hpp:4,
                 from simdjson.cpp:5:
/home/eregon/.rubies/ruby-2.6.5/include/ruby-2.6.0/ruby/intern.h:56:33: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
 void rb_mem_clear(register VALUE*, register long);
                                 ^
/home/eregon/.rubies/ruby-2.6.5/include/ruby-2.6.0/ruby/intern.h:56:45: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
 void rb_mem_clear(register VALUE*, register long);
                                             ^~~~

Since the warning comes from ruby/intern.h it should be fixed in TruffleRuby, as done in MRI in ruby/ruby@113bef6.

[deepj]

@eregon Ah, I tested it only on MRI 2.7.0 where it works

$ gem install simdjson
Fetching simdjson-0.2.0.gem
Building native extensions. This could take a while...
Successfully installed simdjson-0.2.0
1 gem installed
$ ruby -v
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin18]