I have a Rust project that follows a structure:
- main_crate (features = "x")
- driver_crate (features = "x")
- x_crate
...
...
In my main_crate, I have a feature flag x that I enable by default which is propagated to the driver_crate via the following setup in main_crate/Cargo.toml:
[features]
x = ["driver-crate/x"]
# default = ["x"]
The driver_crate/Cargo.toml specifies the x dependency as optional in the following way:
[dependencies]
x-crate = { path = "../x-crate", optional = true }
[features]
x = ["dep:x-crate"]
Suppose that I run cargo build --no-default-features, my expectation is that now that x is no longer enabled by default, Cargo should now treat the x dependency as false and hence not even attempt to compile it as part of the project. Instead, cargo still adds x_crate as part of the compilation process.
Furthermore, I verified that "x" crate is not in the "dependency" tree when I do the following command:
cargo tree -p main_crate | grep "x_crate"
It is however present when I specifically enable x:
cargo tree -p main_crate -F "x" | grep "x_crate"
│ │ ├── x_crate v0.1.0 (/src/x_crate)
Is there a way to ensure that x_crate is not compiled at all when feature x is not specified?
Update: I realised why it's included in the compilation. My project is using a virtual manifest that specifies that the members of the workspace are src/* which automatically includes x:
[workspace]
members = [
"src/*",
How can I dynamically include/exclude x_crate as a dependency when I specify x feature flag to the workspace?
The crate is being compiled because in a workspace, Cargo by default builds all packages.
You can build only a specific package (and its dependencies) with cargo build --package <package> (cargo build -p <package>), or set a default package for all cargo builds via workspace.default-members.