Constraints prevent packages from depending on each other in ways that don’t make sense but are allowed by your package manager. They help you maintain a dependency graph that’s easy to reason about no matter how many packages are in your project. You might want to use constraints to:
  • Ensure no package can ever depend on an application
  • Ensure data packages can’t depend on ui packages
  • Ensure config packages can only depend on other config packages.

​
Configuring constraints

Constraints are defined as a constraint object in your project configuration file and can be used to allow and disallow packages matching a selector. Here’s an example of a configuration that enforces the constraints above:
.commonality/config.json
{
  "$schema": "https://commonality.co/config.json",
  "constraints": {
    "*": {
      "disallow": ["deployable"]
    },
    "data": {
      "disallow": ["ui"]
    },
    "config": {
      "allow": ["config"]
    }
  }
}

​
Validating constraints

You can view the status of your constraints by running the constraint command. 
commonality constrain

​
Precedence

A constraint object can contain both allow and disallow constraints. When both are present, disallow constraints will be evaluated first.