Don't derive Copy in FFI structs/unions that contain pointers

[sdroege]

Clone is still derived to as explicitly cloning the structs is less of a
problem, but implicitly copying them can easily cause double frees.

Fixes #1048

[sdroege]

See gtk-rs/gtk3-rs#289 for the regenerate PR.

[sdroege]

Not complete apparently. If a struct contains a field that does not implement Copy, we still consider it Copy sometimes.

[GuillaumeGomez]

Do you have an example by any chance?

[sdroege]

error[E0204]: the trait `Copy` may not be implemented for this type
    --> glib/sys/src/lib.rs:1044:10
     |
1044 | #[derive(Copy, Clone)]
     |          ^^^^
1045 | pub union GVariantBuilder_u {
1046 |     pub s: GVariantBuilder_u_s,
     |     -------------------------- this field does not implement `Copy`
     |
     = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

Another problem is also:

error[E0658]: unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable
    --> glib/sys/src/lib.rs:1046:5
     |
1046 |     pub s: GVariantBuilder_u_s,
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = note: see issue #55149 <https://github.com/rust-lang/rust/issues/55149> for more information

[GuillaumeGomez]

Oh, interesting.

[sdroege]

I think considering that limitation for unions, we can't actually do anything meaningful here yet...

[sdroege]

Closing as blocked on rust-lang/rust#55149