Records in normal mode

[EPashkin]

Part of #102
Seems records will more difficult that I think.

• Its needed wrapper (analog of Object but maybe without inheritance).
• Also needed autogenerated file with wrapping ffi types. Not sure better do one file for all records in gtk_sys or separate some (with functions) or all.
• when record act as in parameter then it passed by reference and translated with to_glib_none.
• act as return then it optioned and translated with from_glib_none()

[gkoz]

We seem to be going down the one struct per file path so it makes sense to do the same with records.

Wrapping them is a bit more difficult mostly because some of them are refcounted (ref/unref methods) and others (let's call them owned) are not (copy/free). Can't say if using generics is worth it. Possibly. We obviously don't want to expose any of (ref, unref, copy, free, and possibly more).

The owned records have to be taken as arguments by &mut not &. And I haven't really explored the implications for the translate API, but I expect it to work.

The kind of ownership transfer (none/full) we know.

[gkoz]

The owned records have to be taken as arguments by &mut not &.

Unless the function takes a const *.

[gkoz]

Theoretically, if an owned record is passed as an argument with transfer: full we could take the wrapper by value (consume). No idea how many such cases there actually are.

[gkoz]

Some "Boxed" types support has been added. A completely opaque struct can be represented now. Other kinds need more thinking.

[EPashkin]

6 owned(boxed) records without fields: IconSource(deprecated 3.10), PaperSize, SelectionData(no constructor), TreePath, TreeRowReference(no external usage), WidgetPath(has copy, free, ref, unref).
5 with fields: Border, Requisition(width,height), TargetEntry, TextIter(all fields dummy), TreeIter(also).
1 without glib:get-type: StockItem (fields, deprecated 3.10).

Some have only copy, ref, unref: IconSet(deprecated 3.10), TextAttributes, so it don't count as boxed.
I try write generation for first 6 with PaperSize as start.

[gkoz]

While the owned and refcounted records need slightly different wrappers, the difference probably doesn't matter for the conversions code.

The caller-allocates attribute, that is currently ignored, impacts the outparams records conversions.

caller-allocates="0" transfer-ownership="xyz":

    let mut ptr = ptr::null_mut();
    ffi::func(&mut ptr);
    from_glib_xyz(ptr)

caller-allocates="1" transfer-ownership="none":

    let mut rec = Rec::uninitialized();
    ffi::func(rec.to_glib_none_mut().0);
    rec

[gkoz]

Now, there also are "plain old data" records like GdkRectangle and GtkAccelKey that probably don't need any conversions but are passed by pointer.

[gkoz]

So, there now exist Boxed and Refcounted wrappers but a big issue with Boxed records is that

• they often have to be borrowed mutably (to_glib_none_mut),
• there needs to be a way to override the above and use immutable borrow despite the function taking *mut (see Use the glib_wrapper! macro and wrap TreeIter gtk#176 (comment)).