[Libguestfs] [PATCH 0/6] Allow non-optargs functions to gain optional arguments.

[Richard W.M. Jones]

This rather complex set of patches allow non-optargs functions to gain
optional arguments, while preserving source and binary backwards
compatibility.

The problem is that we cannot add an optional argument to an existing
function.  For example, we might want to add flags to the 'lvresize'
API which currently has no optional arguments.

  http://libguestfs.org/guestfs.3.html#guestfs_lvresize

The reason this wouldn't be possible is because in C the call is
specified as:

  int guestfs_lvresize (guestfs_h *g, const char *device, int mbytes);

which leaves no scope for extra parameters to be added.  However in
other languages, it wouldn't be a problem, eg. in Perl you can
overload functions with additional arguments perfectly happily:

  $g->lvresize (device, mbytes);
  $g->lvresize (device, mbytes, free_percent => 50);

and this is true in most non-C languages.

The way to make this work is to generate C bindings differently.  We
would still generate the (backwards-compatible) guestfs_lvresize
function as before, but we would generate an additional function
'guestfs_lvresize_opts' which could take optional arguments.

Additionally, there are three "*-opts" APIs already (add-drive-opts,
mkfs-opts, ntfsresize-opts).  By luck, all of these have "non-opts"
variants which take all the same required arguments.  Therefore we can
rename these as non-opts functions (add-drive, mkfs, ntfsresize) and
use the same machinery above to generate the "*-opts" variants
automatically.  Existing callers will not be affected.

The patches in this series do just this:

1/6, 2/6: Adds a 'once_had_no_optargs' flag to the generator, allowing
functions to be transitioned from non-opts -> opts.  This flag must be
set to true when this is done so the corresponding backwards-
compatibility functions can be generated.

3/6: Adds *-opts aliases in non-C languages.  This ensures that non-C
bindings won't be broken by this transition.  *NB* PHP, Haskell and
GObject bindings *are* broken at the moment; see the notes in the
commit message.

4/6, 5/6, 6/6: Rename add-drive-opts -> add_drive, mkfs-opts -> mkfs,
ntfsresize-opts -> ntfsresize.  By setting the once_had_no_optargs
flag we avoid breaking code for callers.

----

At the moment, the GObject bindings don't run at all on Rawhide.  I
suspect this is a general bug in Rawhide, since it doesn't happen on
F17.  The error is:

    JS ERROR: !!!   Exception was: Error: Unsupported type void, deriving from fundamental void
    JS ERROR: !!!     message = '"Unsupported type void, deriving from fundamental void"'
    JS ERROR: !!!     fileName = '"./bindtests.js"'
    JS ERROR: !!!     lineNumber = '27'
    JS ERROR: !!!     stack = '"@./bindtests.js:27

Rich.