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Binary Caching

Xcode's build system is designed for incremental builds, enhancing efficiency under normal circumstances. However, this feature falls short in Continuous Integration (CI) environments, where data essential for incremental builds is not shared across different builds. Additionally, developers often reset this data locally to troubleshoot complex compilation problems, leading to more frequent clean builds. This results in teams spending excessive time waiting for local builds to finish or for Continuous Integration pipelines to provide feedback on pull requests. Furthermore, the frequent context switching in such an environment compounds this unproductiveness.

Tuist addresses these challenges effectively with its binary caching feature. This tool optimizes the build process by caching compiled binaries, significantly reducing build times both in local development and CI environments. This approach not only accelerates feedback loops but also minimizes the need for context switching, ultimately boosting productivity.

BINARY CACHING AND TUIST SUSTAINABILITY

Be aware that sharing binaries across environments is not possible without Tuist Cloud. We've designed this feature to secure funding for the Tuist projct, which we couldn't achieve with the traditional open-source model. Attempts to work around this limitation may impact the sustainability of the project, which might impact your ability to use Tuist in the future.

Cache warming

Tuist efficiently utilizes hashes for each target in the dependency graph to detect changes. Utilizing this data, it builds and assigns unique identifiers to binaries derived from these targets. At the time of graph generation, Tuist then seamlessly substitutes the original targets with their corresponding binary versions.

This operation, known as "warming," produces binaries for local use or for sharing with teammates and CI environments via Tuist Cloud. The process of warming the cache is straightforward and can be initiated with a simple command:

bash
tuist cache

The command re-uses binaries to speed up the process.

Using the cache binaries

By default, when Tuist commands necessitate project generation, they automatically substitute dependencies with their binary equivalents from the cache, if available. Additionally, if you specify a list of targets to focus on, Tuist will also replace any dependent targets with their cached binaries, provided they are available. For those who prefer a different approach, there is an option to opt out of this behavior entirely by using a specific flag:

bash
tuist generate # Only dependencies
tuist generate Search # Dependencies + Search dependencies
tuist generate Search Settings # Dependencies, and Search and Settings dependencies
tuist generate --no-binary-cache # No cache at all
bash
tuist test

WARNING

Binary caching is a feature designed for development workflows such as running the app on a simulator or device, or running tests. It is not intended for release builds. When archiving the app, generate a project with the sources by using the --no-binary-cache flag.

Cacheable products

Only the following target products are cacheable by Tuist:

  • Frameworks (static and dynamic) that don't depend on XCTest
  • Bundles
  • Swift Macros

We are working on supporting libraries and targets that depend on XCTest.

UPSTREAM DEPENDENCIES

When a target is non-cacheable it makes the upstream targets non-cacheable too. For example, if you have the dependency graph A > B, where A depends on B, if B is non-cacheable, A will also be non-cacheable.

Cache effectiveness

The level of effectiveness that can be achieved with binary caching depends strongly on the graph structure. To achieve the best results, we recommend the following:

  1. Avoid very nested dependency graphs. The shallower the graph, the better.
  2. Define dependencies with protocol/interface targets instead of implementation ones, and dependency-inject implementations from the top-most targets.
  3. Split frequently-modified targets into smaller ones whose likelihood of change is lower.

The above suggestions are part of the The Modular Architecture, which we propose as a way to structure your projects to maximize the benefits not only of binary caching but also of Xcode's capabilities.

We recommend having a CI job that runs in every commit in the main branch to warm the cache. This will ensure the cache always contains binaries for the changes in main so local and CI branch build incrementally upon them.

CACHE WARMING USES BINARIES

The tuist cache command also makes use of the binary cache to speed up the warming.

The following are some examples of common workflows:

A developer starts to work on a new feature

  1. They create a new branch from main.
  2. They run tuist generate.
  3. Tuist pulls the most recent binaries from main and generates the project with them.

A developer pushes changes upstream

  1. The CI pipeline will run tuist build or tuist test to build or test the project.
  2. The workflow will pull the most recent binaries from main and generate the project with them.
  3. It will then build or test the project incrementally.

Troubleshooting

It doesn't use binaries for my targets

Ensure that the hashes are deterministic across environments and runs. This might happen if the project has references to the environment, for example through absolute paths. You can use the diff command to compare the projects generated by two consecutive invocations of tuist generate or across environments or runs.

Also make sure that the target doesn't depend either directly or indirectly on a non-cacheable target.

Released under the MIT License.