I think that for an option library like uuid, its feature can be reexported at the same time.

[driftluo]

Issue:

Diesel 1.1.* only support uuid 0.5.*, and I use uuid need its v4 feature, so on my Cargo.toml will be:

[dependencies.uuid]
features = ["serde", "v4"]
version = "^0.5.0"

[dependencies.diesel]
features = ["postgres", "chrono", "uuid", "r2d2"]
version = "^1.1.1"

But diesel 1.2.* support to uuid 0.6.*, when I cargo update, uuid doesn't update to 0.6, then will Rustc will complain like follow:

error[E0277]: the trait bound `uuid::Uuid: diesel::Expression` is not satisfied
 --> src\models\article_tag_relation.rs:9:10
  |
9 | #[derive(Insertable, Debug, Clone, Deserialize, Serialize)]
  |          ^^^^^^^^^^ the trait `diesel::Expression` is not implemented for `uuid::Uuid`
  |
  = note: required because of the requirements on the impl of `diesel::Expression` for `&'insert uuid::Uuid`
  = note: required because of the requirements on the impl of `diesel::expression::AsExpression<diesel::sql_types::Uuid>` for `&'insert uuid::Uuid`

So, I think that for an option library like uuid, its feature can be reexported at the same time. In this way, you do not need to pay attention to the version of the corresponding library, let it upgrade at the same time with the diesel.

If you accept this view, I will submit a pull request to complete this function.

[sgrif]

This wouldn't solve your original problem, as the v4 feature would not be enabled since the versions don't match up.

[driftluo]

However, when I write it like this, my project is working properly:

[dependencies.uuid]
features = ["serde", "v4"]
version = "^0.6.0"

[dependencies.diesel]
features = ["postgres", "chrono", "uuid", "r2d2"]
version = "^1.1.1"

On Cargo.lock , only a 0.6.3 version of the uuid library.

I think diesel features add the following:

[features]
v4 = ["uuid/v4"]

I will be able to use this instead of reimport the uuid library just to turn on an features：

[dependencies.diesel]
features = ["postgres", "chrono", "uuid", "r2d2", "v4"]
version = "^1.1.1"

[driftluo]

Ok, I looked at the source code, uuid is converted from trait FromSql IntoSql, not the corresponding type in the uuid crate, there seems to be no way to inherit the feature, this is my idealization, I underestimated the complexity of the problem, but this is not something that cannot be achieved

[sgrif]

I do not want to re-export every feature of every optional dependency we support

[sgrif]

While I can appreciate the sentiment here, I don't think this approach makes sense in Diesel. For most applications, they will likely want to enable at least one feature on the other crates (usually serde). This requires syncing versions. There's really no way around it.