rustc will start looking behind `#[cfg(FALSE)]` items to start giving
better diagnostics. By using an explicit re-export instead of a glob
export, we tell rustc that `Deserialize` and `Serialize` exist here.
This works just fine if we make syn parse "where " as a syn::WhereClause.
The serde(bound = "") attribute is definitely not common enough that it
would warrant a micro-optimization.
Without serde(bound = ""), serde_derive infers a bound of `T: Serialize`
for the generated Serialize impl and `T: Deserialize<'de> + Default` for
the Deserialize impl. `X` implements none of these so the generated code
would fail to compile.
error[E0277]: the trait bound `X: Serialize` is not satisfied
--> test_suite/tests/test_gen.rs:268:14
|
268 | assert::<PhantomDataWrapper<X>>();
| ^^^^^^^^^^^^^^^^^^^^^ the trait `Serialize` is not implemented for `X`
|
= help: the following other types implement trait `Serialize`:
&'a T
&'a mut T
()
(T0, T1)
(T0, T1, T2)
(T0, T1, T2, T3)
(T0, T1, T2, T3, T4)
(T0, T1, T2, T3, T4, T5)
and 248 others
note: required for `PhantomDataWrapper<X>` to implement `Serialize`
--> test_suite/tests/test_gen.rs:262:14
|
262 | #[derive(Serialize, Deserialize)]
| ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
263 | //#[serde(bound = "")]
264 | struct PhantomDataWrapper<T> {
| ^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `assert`
--> test_suite/tests/test_gen.rs:767:14
|
767 | fn assert<T: Serialize + DeserializeOwned>() {}
| ^^^^^^^^^ required by this bound in `assert`
= note: this error originates in the derive macro `Serialize` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0277]: the trait bound `X: Deserialize<'_>` is not satisfied
--> test_suite/tests/test_gen.rs:268:14
|
268 | assert::<PhantomDataWrapper<X>>();
| ^^^^^^^^^^^^^^^^^^^^^ the trait `Deserialize<'_>` is not implemented for `X`
|
= help: the following other types implement trait `Deserialize<'de>`:
<&'a Path as Deserialize<'de>>
<&'a [u8] as Deserialize<'de>>
<&'a str as Deserialize<'de>>
<() as Deserialize<'de>>
<(T0, T1) as Deserialize<'de>>
<(T0, T1, T2) as Deserialize<'de>>
<(T0, T1, T2, T3) as Deserialize<'de>>
<(T0, T1, T2, T3, T4) as Deserialize<'de>>
and 331 others
note: required for `PhantomDataWrapper<X>` to implement `for<'de> Deserialize<'de>`
--> test_suite/tests/test_gen.rs:262:25
|
262 | #[derive(Serialize, Deserialize)]
| ^^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
263 | //#[serde(bound = "")]
264 | struct PhantomDataWrapper<T> {
| ^^^^^^^^^^^^^^^^^^^^^
= note: required for `PhantomDataWrapper<X>` to implement `DeserializeOwned`
note: required by a bound in `assert`
--> test_suite/tests/test_gen.rs:767:26
|
767 | fn assert<T: Serialize + DeserializeOwned>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `assert`
= note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0277]: the trait bound `X: Default` is not satisfied
--> test_suite/tests/test_gen.rs:268:14
|
268 | assert::<PhantomDataWrapper<X>>();
| ^^^^^^^^^^^^^^^^^^^^^ the trait `Default` is not implemented for `X`
|
note: required for `PhantomDataWrapper<X>` to implement `for<'de> Deserialize<'de>`
--> test_suite/tests/test_gen.rs:262:25
|
262 | #[derive(Serialize, Deserialize)]
| ^^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
263 | //#[serde(bound = "")]
264 | struct PhantomDataWrapper<T> {
| ^^^^^^^^^^^^^^^^^^^^^
= note: required for `PhantomDataWrapper<X>` to implement `DeserializeOwned`
note: required by a bound in `assert`
--> test_suite/tests/test_gen.rs:767:26
|
767 | fn assert<T: Serialize + DeserializeOwned>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `assert`
= note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider annotating `X` with `#[derive(Default)]`
|
779 | #[derive(Default)]
|
This function is called for untagged, internally and externally tagged enums,
but `deserializer` parameter is `None` only for the latest. Only when it's `None`
`DeserializeSeed` impl is used
