version.c: show +JIT when --jit is passed

in version output.
version.h: ditto
ruby.c: propagate option for it
common.mk: updated dependency for version.c

mjit.c: overwrites the RUBY_DESCRIPTION to have +JIT when --jit is passed

test/ruby/test_rubyoptions.rb: add test for them

Only `ruby --jit -v` will have "+JIT", but this is intentional.
This may not be convenient for debugging by ticket with `ruby -v`,
but it's convenient for benchmark tools that pass options (--jit)
when showing it. At least such behavior is planned for benchmark_driver.gem
and this behavior is designed for it. Other benchmark tools are
recommended to follow the behavior too if they show version.
RUBY_DESCRIPTION might be useful for it too.

The position of "+JIT" is changed from original proposal because other
platforms like JRuby and TruffleRuby end it with archtecture.
It's made similar to JRuby, but it's upper-cased because Matz made approval
for "+JIT" in the ticket.

Example:
$ ruby -v
ruby 2.6.0dev (2018-02-22 trunk 62529) [x86_64-linux]
$ ruby --jit -v
ruby 2.6.0dev (2018-02-22 trunk 62529) +JIT [x86_64-linux]

After --jit is made default in the future, this output may be removed.
So do not rely on this output if possible.

[Feature #14462]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62530 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 9 insertions, 0 deletions

diff --git a/mjit.c b/mjit.c
index 502769c52b..b8cb4f5424 100644
--- a/mjit.c
+++ b/mjit.c
@@ -1314,12 +1314,16 @@ system_tmpdir(void)
 /* Minimum value for JIT cache size.  */
 #define MIN_CACHE_SIZE 10
 
+extern const char ruby_description_with_jit[];
+
 /* Initialize MJIT.  Start a thread creating the precompiled header and
    processing ISeqs.  The function should be called first for using MJIT.
    If everything is successfull, MJIT_INIT_P will be TRUE.  */
 void
 mjit_init(struct mjit_options *opts)
 {
+    VALUE rb_description;
+
     mjit_opts = *opts;
     mjit_init_p = TRUE;
 
@@ -1366,6 +1370,11 @@ mjit_init(struct mjit_options *opts)
         rb_id_table_foreach(RCLASS_CONST_TBL(rb_cObject), valid_class_serials_add_i, NULL);
     }
 
+    /* Overwrites RUBY_DESCRIPTION constant */
+    rb_const_remove(rb_cObject, rb_intern("RUBY_DESCRIPTION"));
+    rb_description = rb_usascii_str_new_static(ruby_description_with_jit, strlen(ruby_description_with_jit));
+    rb_define_global_const("RUBY_DESCRIPTION", rb_obj_freeze(rb_description));
+
     /* Initialize worker thread */
     finish_worker_p = FALSE;
     worker_finished = FALSE;