There's actually a third alternative, called Git X-Modules (https://gitmodules.com). It's a tool to release the PIA submodules are causing, as described in may comment above :-)
In short, it takes all synchronization to the server's side. So you can combine repositories together in any way you like, and still work with a multi-module repository as if it was a regular one - no special commands, specific course of actions, etc.
Git X-Modules is a server-side app that syncs your project directories with other repositories. Think of it as a server-side alternative to Git Submodules.
Use Cases:
- Combine multiple projects and components into a single repository for cross-project development (like a monorepo, but keeping the original repositories up and running)
- Include parts of other projects into yours
- Share common assets across multiple projects
How it works:
- An X-Module is a regular directory. It’s synced on your Git server with an external repository.
- When an X-Module is updated the changes go to the external repository.
- When an external repository is updated the changes are applied to the X-Module.
- When there are two conflicting updates Git X-Modules applies one update and turns the other into a pull request
This tool is available as a free GitHub app. There's also an app for Bitbucket DataCenter (self-hosted).
Some of the real-life cases we've heard of:
- Code review team wants to see all changes made in various repositories, in one place
- A private project contains an open-source part, that is shared in a separate repository
- A library or component is maintained in a separate repository and shared between several projects
Both approaches have their good and bad sides. There is, however, a way to combine the advantages of both ways, having a monorepo synchronized with multiple individual repositories by Git X-Modules(https://gitmodules.com).
I am a part of the team behind it, so AMA about the tool :-)