Parallel Incremental Builds Not Working Across Projects in Xcode

[chiragramani]

We are experiencing an issue where incremental builds in a multi-project setup within Xcode run serially instead of in parallel. While we observe parallel builds for targets within the same workspace/project, projects with dependencies across different Xcode projects only build sequentially.

We would like to understand the recommended way to configure project dependencies - such as shared build directory settings or any other relevant configurations, so that we can achieve the same level of parallelism for cross-project references as we do for targets within the same workspace/project.

Repro: https://github.com/chiragramani/Xcode-Serial-Incremental-Builds

Additional Context

1. When we first reported this issue, parallel builds weren't even working for targets within the same project. It looks like that problem has now been resolved(sharing as it might related). Link
2. In the above repro, we see partial incremental builds with how projects are generated with tuist but not with Xcode. We are unsure what we are missing and what's recommended from a build system point of view, so that we can add the recommended configuration.