Error running 'make ', please check /Users/home_dir/.rvm/log/ruby-1.9.1-p378/make*.log
The error in ~/.rvm/log/ruby-1.9.1-p378/make*.log:
compiling readline
readline.c: In function ‘username_completion_proc_call’:
readline.c:1159: error: ‘username_completion_function’ undeclared (first use in this function)
readline.c:1159: error: (Each undeclared identifier is reported only once
readline.c:1159: error: for each function it appears in.)
make[1]: *** [readline.o] Error 1
make: *** [mkmain.sh] Error 1
So compiling Ruby 1.9.1 with the default readline installed on Snow Leopard didn't work.
By looking at "rvm --help" or ~/.rvm/README, there is an option to specify custom configure options, i.e. -C|--configure. Also there is a flag to force ./configure on install even if Makefile already exists, i.e. --reconfigure.
So I installed readline with MacPorts and installed Ruby 1.9.1 with the option and the flag:
$ sudo port install readline
$ rvm install 1.9.1 --reconfigure --configure --with-readline-dir=/opt/local
Then installation succeeded.