Cannot add component of type:CustomObject to another package because it is an installed component

Question

I created a package and now I want to create a dependent package. Let's say the parent package has a custom object: namespace__Application__c

In my child package, under the objects directory, I have: namespace__Application__c/fields/

which is a directory of new fields to be added to the object.

When I try to install the package, I get the following error:

package.xml: Cannot add component of type:CustomObject named:namespace__Application__c subjectId:01IP0000000Iz59 to another package because it is an installed component.

The parent package is already installed and the child package gets compiled with no errors, but this happens when I try to install it.

I can only find one more result here but it's a different problem.

Details about the environment:

1. Both packages are attached to the same dev hub
2. Both packages created with this command: sfdx force:package:version:create --package PackageName --path force-app --installationkey XXXXX --wait 10 --definitionfile config/project-scratch-def.json
3. I'm trying to install them to a temporary scratch org - the parent package installs fine, the child package fails

Here's the sfdx-project.json

    "packageDirectories": [
        {
            "path": "force-app",
            "default": true,
            "package": "ChildPackage",
            "versionName": "ver 0.2",
            "versionNumber": "0.2.0.NEXT",
            "dependencies": [
                {
                    "package": "[email protected]"
                }
            ]
        }
    ],
    "namespace": "namespace",
    "sfdcLoginUrl": "https://login.salesforce.com",
    "sourceApiVersion": "47.0",
    "packageAliases": {
        "ChildPackage": "0HoXXX",
        "[email protected]": "04tXXX",
        ... multiple versions of ChildPackage ...
        "[email protected]": "04tXXX"
    }
}```

Answer 1

For your 2GP packages, you need to use the name/versionNumber format for your dependencies:

"dependencies": [
    {
        "package": "ParentPackage",
        "versionNumber": "0.1.0.LATEST"
    }
]

It took me a little while to figure this out myself.

Also, make sure you do not have an object-meta.xml file in the root of each object folder for the child packages. It should contain only field metadata.