I am fairly new to rust and am trying to understand how best to create re-useable shared library components. I have a github repo named rust-libs that is setup as a cargo workspace. The project tree for this repo looks like this:
├── Cargo.lock
├── Cargo.toml
├── describable
│ ├── Cargo.toml
│ └── src
│ ├── describable.rs
│ └── lib.rs
└── health_check
├── Cargo.toml
└── src
├── health_check.rs
└── lib.rs
where the top-level Cargo.toml file contains:
[workspace]
members = [
"describable",
"health_check"
]
The Cargo.toml file in each member just defines the dependencies of that member and its version - e.g. describable/Cargo.toml:
[package]
name = "lib_describable"
version = "1.0.0"
authors = ["my-name <me@email.com>"]
edition = "2018"
[lib]
name = "lib_describable"
path = "src/lib.rs"
and health_check/Cargo.toml:
[package]
name = "lib_health_check"
version = "1.0.0"
authors = ["my-name <me@email.com>"]
edition = "2018"
[dependencies]
lib_describable = { path = "../describable" }
[lib]
name = "lib_health_check"
path = "src/lib.rs"
Note that I am naming the library with a lib_ prefix just to avoid any clashes with other rust libraries.
The lib.rs file in each workspace member just defines the public modules I want to export - e.g. describable/src/lib.rs:
pub mod describable;
The implementation for this is in describable/src/describable.rs:
pub trait Describable {
fn describe(&self) -> String;
}
The implementation in health_check/src/health_check.rs is:
use lib_describable::describable::Describable;
pub trait HealthCheckable: Describable {
fn check_health(&mut self) -> Result<(), String>;
}
When making any changes to a specific member, I always update its version number in its Cargo.toml file. CircleCI is used to automatically build this repo. If the build is successful, then the CircleCI job tags this repo with a multiple git tags (one per member in the workspace) and these tags are of the form <member-name>_<member-version-from-its-cargo-toml>_<git-short-commit-sha>, e.g. for the above two members it might tag the build with these tags:
describable_1.0.0_d2db9ff
health_check_1.0.0_d2db9ff
I then have a separate git repo that contains a rust binary that is built that makes use of these shared library members. The project refers to the shared library members in its Config.toml as follows:
...
[dependencies]
...
lib_describable = { git = "ssh://git@github.com/xxx/rust-libs.git", tag = "describable_1.0.0_d2db9ff" }
lib_health_check = { git = "ssh://git@github.com/xxx/rust-libs.git", tag = "health_check_1.0.0_d2db9ff" }
...
[[bin]]
name = "my-app"
path = "src/bin/main.rs"
xxx is just the obfuscated name of my github account. The file src/bin/main.rs in this project contains code of the form:
extern crate lib_describable;
extern crate lib_health_check;
use lib_describable::describable::Describable;
use lib_health_check::health_check::HealthCheckable;
pub trait MyDb: Describable + HealthCheckable {
// some functions defined here that are not important for this issue
}
pub struct MySpecialDb { ... }
impl Describable for MySpecialDb {
fn describe(&self) -> String {
// returns a description of this DB
}
}
impl HealthCheckable for MySpecialDb {
fn check_health(&mut self) -> Result<(), String> {
// performs some health check specific to this DB and returns either Ok(()) if its healthy or Err("...some error message...") if it is unhealthy
}
}
impl MyDb for MySpecialDb { ... }
The problem I am finding is that the rust compiler does not seem to like the line impl HealthCheckable for MySpecialDb and reports an error of the form:
the trait bound `...::MySpecialDb: lib_describable::describable::Describable` is not satisfied
the trait `lib_describable::describable::Describable` is not implemented for `...::MySpecialDb`
note: perhaps two different versions of crate `lib_describable` are being used?rustc(E0277)
Is there something obvious that I am doing wrong here to cause this error?
