ng update migrations not working on npm linked custom schematics

[bmayen]

🐞 Bug report

Command (mark with an x)

- [x] update

Description

I have custom schematics to generate a new application using ng new -c my-custom-schematics. I am attempting to add migrations so I can update my applications when the schematics are updated, using ng update my-custom-schematics. During development of these migrations, if I npm link my-custom-schematics in the generated application and run ng update my-custom-schematics --migrate-only --from=1 I receive the error "Package found in package.json but is not installed." If I copy the package to the application's node_modules folder, it works fine. The problem only arises using npm link.

🔬 Minimal Reproduction

1. Generate a new application using custom schematics.
2. Update the schematic to include migrations to a new version.
3. npm link the application to the new version of the schematics
4. Run ng update my-custom-schematics --migrate-only --from=1

🔥 Exception or Error

Package found in package.json but is not installed.

Anything else relevant?

Not receiving the error if I copy the package to the application's node_modules folder. Only occurs if the schematics package is npm linked.

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