current directory: /home/kk/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/json-1.8.3/ext/json/ext/generator
make "DESTDIR="
compiling generator.c
generator.c: In function ‘generate_json’:
generator.c:861:25: error: ‘rb_cFixnum’ undeclared (first use in this function); did you mean ‘mFixnum’?
861 | } else if (klass == rb_cFixnum) {
| ^~~~~~~~~~
| mFixnum
generator.c:861:25: note: each undeclared identifier is reported only once for each function it appears in
generator.c:863:25: error: ‘rb_cBignum’ undeclared (first use in this function); did you mean ‘mBignum’?
863 | } else if (klass == rb_cBignum) {
| ^~~~~~~~~~
| mBignum
generator.c: At top level:
cc1: warning: unrecognized command line option ‘-Wno-self-assign’
cc1: warning: unrecognized command line option ‘-Wno-parentheses-equality’
cc1: warning: unrecognized command line option ‘-Wno-constant-logical-operand’
make: *** [Makefile:245: generator.o] Error 1
make failed, exit code 2
Using rbenv on Ubuntu.