examples: Add stricter impl trait bounds

[felinira]

Separates out the examples as those don't introduce breaking changes.

See #1515

[sdroege]

This one is not inferred by requiring PetImpl, and PetImpl requiring IsA<Pet>?

[felinira]

It is required, not inferred. Therefore it is showing an error if not specified.

[felinira]

error[E0277]: the trait bound `<Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/cat.rs:99:20
    |
99  | pub trait CatImpl: PetImpl
    |                    ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Self as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
101 |     <Self as ObjectSubclass>::Type: IsA<Cat>, <Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>
    |                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error[E0277]: the trait bound `<Obj as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/cat.rs:106:28
    |
106 | unsafe impl<Obj: CatImpl + PetImpl> IsSubclassable<Obj> for Cat where
    |                            ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Obj as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
107 |     <Obj as ObjectSubclass>::Type: IsA<Cat>, <Obj as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>
    |                                            +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `gtk-rs-examples` (bin "virtual_methods") due to 2 previous errors

[sdroege]

Not necessary (because nothing else can implement this trait) unless the compiler forces you :) It should also be implied via T: PetImpl already

[felinira]

unless the compiler forces you

It does.

error[E0277]: the trait bound `<Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/pet.rs:154:23
    |
154 | pub trait PetImplExt: PetImpl {
    |                       ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Self as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
154 | pub trait PetImplExt: PetImpl where <Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet> {
    |                               ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

error[E0277]: the trait bound `<T as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/pet.rs:175:9
    |
175 | impl<T: PetImpl> PetImplExt for T {}
    |         ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<T as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
175 | impl<T: PetImpl> PetImplExt for T where <T as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet> {}
    |                                   +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

error[E0277]: the trait bound `<Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/pet.rs:154:23
    |
154 | pub trait PetImplExt: PetImpl {
    |                       ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Self as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
156 |     fn parent_pet(&self) -> bool where <Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet> {
    |                                  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

error[E0277]: the trait bound `<Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/pet.rs:154:23
    |
154 | pub trait PetImplExt: PetImpl {
    |                       ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Self as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
165 |     fn parent_feed(&self) where <Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet> {
    |                           ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `gtk-rs-examples` (bin "virtual_methods") due to 4 previous errors