How to deal with multiple nested workspace roots?

Question

How can you have multiple nested workspace with Cargo?

I have the following project structure:

myworkspace
├── project_a
│   └── Cargo.toml
├── project_b
│   └── Cargo.toml
│   └── project_b_dependency
|       └── Cargo.toml
└── Cargo.toml

Where project_b_dependency is a big library which is a git submodule which has a workspace by itself.

I get an error when I run cargo build because there is a workspace within a workspace.

$ cargo build
error: multiple workspace roots found in the same workspace:
  /myworkspace
  /myworkspace/project_b/project_b_dependency

Is there a simple work-around? I want to keep project_b_dependency in source control as a submodule.

This is not a duplicate of Refactoring to workspace structure causes extern crate imports to not work because I want to know how I can deal with nested workspaces.

Answer 1

It seems that nested workspaces are quite difficult to manage, so one possibility is to change the layout of you project:

.
├── myworkspace
│   ├── Cargo.lock
│   ├── Cargo.toml
│   ├── project_a
│   │   ├── Cargo.toml
│   │   └── src
│   │       └── lib.rs
│   ├── project_b
│   │   ├── Cargo.toml
│   │   └── src
│   │       └── lib.rs
│   └── src
│       └── main.rs
└── project_b_dependency
    ├── Cargo.toml
    └── src
        └── lib.rs

in myworkspace/Cargo.toml:

[workspace]
members= ["project_a", "project_b"]

In myworkspace/project_b/Cargo.toml

[dependencies]
project_b_dependency = {path = "../../project_b_dependency"}

I've tried to use workspace.exclude property with your layout but without success.