Bazel Refetching Dependencies: UTF-8 Error And Solution

Bazel, a popular open-source build tool, is known for its efficiency and reproducibility. However, users sometimes encounter issues that can impact build performance. One such issue arises when Bazel refetches dependencies after each shutdown due to the flag --incompatible_enforce_starlark_utf8=error. This article delves into this specific problem, exploring its causes, potential solutions, and providing a comprehensive understanding to help developers overcome this hurdle.

Understanding the Issue: --incompatible_enforce_starlark_utf8=error

To grasp the root of the problem, let's first understand the role of the --incompatible_enforce_starlark_utf8 flag in Bazel. This flag controls how Bazel handles UTF-8 encoding in Starlark files. Starlark is the configuration language used by Bazel to define build rules. When --incompatible_enforce_starlark_utf8=error is set, Bazel strictly enforces UTF-8 encoding in Starlark files. Any file that doesn't adhere to UTF-8 encoding will cause Bazel to throw an error. While enforcing UTF-8 is generally a good practice for consistency and to avoid encoding-related issues, it can sometimes lead to unexpected behavior, especially when dealing with external dependencies.

When Bazel encounters a Starlark file that is not UTF-8 encoded under the --incompatible_enforce_starlark_utf8=error setting, it might fail to cache the dependencies correctly. This can result in Bazel refetching these dependencies every time it restarts, significantly increasing build times. This issue often surfaces when projects include external dependencies that may not strictly adhere to UTF-8 encoding. Identifying these non-UTF-8 encoded files can be challenging, especially in large projects with numerous dependencies.

The Refetching Problem: Why It Happens

The core reason for the refetching issue lies in Bazel's dependency caching mechanism. Bazel caches dependencies to avoid redundant downloads and builds, which speeds up subsequent builds. However, when --incompatible_enforce_starlark_utf8=error is active, Bazel might not be able to cache dependencies correctly if any Starlark file in the dependency chain is not strictly UTF-8 encoded. This lack of proper caching forces Bazel to refetch the dependencies on each invocation, leading to significant delays, especially in projects with many external dependencies. The problem is exacerbated in environments where network bandwidth is limited or latency is high.

The impact of this issue can be substantial, particularly in continuous integration (CI) environments where builds are frequent and time-sensitive. Refetching dependencies on every build can negate the benefits of Bazel's caching mechanism, resulting in longer build times and increased resource consumption. This not only affects developer productivity but also the overall efficiency of the CI pipeline.

The Solution: Using --incompatible_enforce_starlark_utf8=warning

One potential solution to this problem is to change the flag setting to --incompatible_enforce_starlark_utf8=warning. This setting tells Bazel to issue a warning when it encounters a non-UTF-8 encoded Starlark file but doesn't treat it as a fatal error. By switching to the warning mode, Bazel can continue to build the project and cache dependencies, avoiding the refetching issue. However, it's important to note that this approach only mitigates the symptom and doesn't address the underlying cause of non-UTF-8 encoding.

While using the warning setting can resolve the immediate refetching problem, it's crucial to eventually address the encoding issues in your project and its dependencies. Leaving the setting on warning indefinitely might mask potential encoding-related bugs that could surface later. Therefore, it's recommended to use the warning setting as a temporary workaround while you work on fixing the underlying encoding problems.

Deeper Dive: Identifying and Fixing Non-UTF-8 Encoded Files

To truly resolve the issue, you need to identify and fix the Starlark files that are not UTF-8 encoded. This can be a challenging task, especially in large projects with numerous dependencies. However, there are several strategies and tools that can help you pinpoint the problematic files.

Using file Command:

The file command in Unix-like systems can be used to detect the encoding of a file. By running file -i <filename>, you can get information about the file's encoding. If the output indicates that the file is not UTF-8 encoded, you've found a potential culprit. This method is particularly useful for quickly checking individual files.

Scripting for Bulk Analysis:

For larger projects, scripting can automate the process of checking multiple files. A simple script can iterate through all Starlark files (.bzl extension) in your project and use the file command to check their encoding. This approach can significantly speed up the process of identifying non-UTF-8 encoded files.

Text Editor Encoding Detection:

Most modern text editors have built-in encoding detection capabilities. Opening a Starlark file in a text editor and checking its encoding can often reveal whether it's UTF-8 encoded or not. Some editors also provide options to automatically convert files to UTF-8 encoding.

Fixing Encoding Issues:

Once you've identified a non-UTF-8 encoded file, you can use various tools to convert it to UTF-8. Text editors often provide options to save files in UTF-8 encoding. Alternatively, command-line tools like iconv can be used to convert file encodings. For example, iconv -f <original_encoding> -t UTF-8 <input_file> -o <output_file> can convert a file from a specific encoding to UTF-8.

Addressing External Dependencies:

If the encoding issue lies in an external dependency, you have a few options. You can try to contact the maintainers of the dependency and request them to fix the encoding. Alternatively, you can create a local patch to fix the encoding in your project. However, patching external dependencies can make it harder to update them in the future, so it's generally better to address the issue upstream if possible.

Best Practices for UTF-8 Encoding in Bazel Projects

To avoid UTF-8 encoding issues in your Bazel projects, it's crucial to follow some best practices:

Enforce UTF-8 Encoding:

Make sure all Starlark files in your project are saved in UTF-8 encoding. This should be a standard practice in your development workflow.

Use a Consistent Encoding:

Stick to UTF-8 encoding throughout your project and its dependencies. Mixing encodings can lead to unexpected issues.

Validate Encoding in CI:

Incorporate encoding validation checks in your CI pipeline. This can help catch encoding issues early in the development process.

Educate Your Team:

Ensure that your team members are aware of the importance of UTF-8 encoding and follow best practices.

Real-World Example: Reproduction Repository

The issue described in the initial bug report includes a reproduction repository: https://github.com/alwaldend/com_github_bazel_contrib_bazelrc_preset_bzl_issues_95. This repository provides a minimal example that demonstrates the refetching problem. By examining this repository, developers can gain a better understanding of the issue and test potential solutions.

Conclusion: Resolving Bazel Dependency Refetching

The issue of Bazel refetching dependencies due to --incompatible_enforce_starlark_utf8=error can significantly impact build performance. While using --incompatible_enforce_starlark_utf8=warning can provide a temporary workaround, the long-term solution involves identifying and fixing non-UTF-8 encoded files. By following best practices for UTF-8 encoding and using appropriate tools, developers can avoid this issue and ensure efficient Bazel builds. Addressing encoding issues not only resolves the refetching problem but also contributes to a more robust and maintainable codebase. Always strive for consistent UTF-8 encoding throughout your project to prevent future complications.

For more information on Bazel and best practices, you can visit the official Bazel documentation: https://bazel.build/.