Hide most of the implementation of `struct rb_io`. (#6511)

* Add rb_io_path and rb_io_open_descriptor.

* Use rb_io_open_descriptor to create PTY objects

* Rename FMODE_PREP -> FMODE_EXTERNAL and expose it

FMODE_PREP I believe refers to the concept of a "pre-prepared" file, but
FMODE_EXTERNAL is clearer about what the file descriptor represents and
aligns with language in the IO::Buffer module.

* Ensure that rb_io_open_descriptor closes the FD if it fails

If FMODE_EXTERNAL is not set, then it's guaranteed that Ruby will be
responsible for closing your file, eventually, if you pass it to
rb_io_open_descriptor, even if it raises an exception.

* Rename IS_EXTERNAL_FD -> RUBY_IO_EXTERNAL_P

* Expose `rb_io_closed_p`.

* Add `rb_io_mode` to get IO mode.

---------

Co-authored-by: KJ Tsanaktsidis <ktsanaktsidis@zendesk.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/debug.c b/debug.c
index d3f41f1a3a..b5cba590ba 100644
--- a/debug.c
+++ b/debug.c
@@ -70,7 +70,7 @@ const union {
         RUBY_FMODE_NOREVLOOKUP		= 0x00000100,
         RUBY_FMODE_TRUNC		= FMODE_TRUNC,
         RUBY_FMODE_TEXTMODE		= FMODE_TEXTMODE,
-        RUBY_FMODE_PREP 		= 0x00010000,
+        RUBY_FMODE_EXTERNAL		= 0x00010000,
         RUBY_FMODE_SETENC_BY_BOM	= FMODE_SETENC_BY_BOM,
         RUBY_FMODE_UNIX 		= 0x00200000,
         RUBY_FMODE_INET 		= 0x00400000,