Commit Messages: Volatile Info and Long-Term Records

The Problem with Volatile Data in Commits

A common scenario in software development involves ensuring that code changes are rigorously verified before being integrated. For instance, a releng script might be tasked with merging a maintenance branch into another, a process that critically depends on the preceding commit passing a verification build. The current approach often relies on a default commit message, such as 'Merge branch release/0.1 into release/0.2'.

To enhance this process, there's a desire to embed proof of verification directly into the commit message. This could take the form of a link to the specific verification build that sanctioned the merge. However, a significant challenge arises from the inherent impermanence of such external references. A verification build, perhaps hosted on a platform like GitHub Actions, might be automatically deleted after a defined period, such as two years, rendering the link defunct.

While this crucial information might also be present in a Pull Request description, PRs themselves can have a shorter lifecycle than the commit history they are associated with, also leading to volatility. The fundamental question then becomes: can a commit message contain information that is only usable for a limited time, and is this a sustainable practice for robust version-control systems?

Commit Messages as Communication

Fundamentally, Git commit messages serve as a form of communication. They are primarily intended as notes to future developers, including one's future self, who will need to understand the context and rationale behind specific changes. A commit message is a breadcrumb trail, meant to guide those who follow through the evolution of the codebase.

The content of a commit message is, technically speaking, unrestricted. One can include informal notes, personal anecdotes, or even references to external resources. The accepted answer on softwareengineering.stackexchange.com suggests that any reference to external information, including ticket numbers, is inherently time-limited. This implies that while not explicitly forbidden, relying on such volatile data introduces a risk.

The crucial consideration is not whether you *can* include volatile information, but rather whether that information will remain accessible and useful for the duration required by your specific needs. The intent behind the commit message—to provide context and justification—must be balanced against the lifespan of the data it references.

Assessing Information Longevity

When embedding links to verification builds or other ephemeral artifacts in commit messages, the primary question becomes one of longevity and utility. Will the referenced external information be available when it's needed, and will the mere presence of a link still be meaningful in the future?

Consider the scenario: a year from now, will you or another developer attempt to follow that specific link to a verification build? Or will the historical record, even with a broken link, be sufficient proof that a defined process was followed at the time of the merge? This assessment is critical for determining the value of including such volatile data.

The decision hinges on the expected lifespan of the need for that information. If the goal is merely to assert that a process *was* followed, a textual reference might suffice. If direct verification is required, then the volatility becomes a significant drawback.

Change Management and Artifact Requirements

The question of including volatile information in commit messages transcends a mere Git technicality; it is fundamentally a challenge in Change Management (CM). The core question is about what artifacts are necessary to support the long-term integrity of the CM process.

Different levels of assurance demand different approaches. If confidence that a process was executed is sufficient, a named reference to volatile information might be adequate. However, if a direct demonstration to a third party, such as a customer, is required, then signing that data or ensuring its permanent archival might be necessary.

The nature of the CM requirements dictates the strategy. For highly regulated environments or stringent auditing, simply referencing a now-deleted build might not pass muster. Exploring solutions like a super-repo that holds onto all artifacts, or integrating with dedicated archival tools, becomes essential for future-proofing the CM process.

Strategies for Archiving Volatile Data

While commit messages themselves are permanent fixtures of the version-control history, the external references they contain are not. If the goal is to retain verifiable proof of a process, such as a verification build, then relying solely on a link within the commit message is insufficient.

Organizations might implement strategies to 'vault' this volatile information. This could involve dedicated systems designed for long-term artifact storage, ensuring that build logs, test results, and other critical data are preserved independently of the source code repository.

Another approach involves external repositories or 'super-repos' that incorporate other repositories as submodules. These can potentially hold onto all associated artifacts indefinitely, although this can lead to significant storage overhead over time. The key is to decouple the verifiable artifact from the ephemeral link within the commit message.

Where This Approach Does Not Fit

Including volatile information, such as links to temporary build artifacts, in commit messages is ill-suited for scenarios demanding strict, long-term auditability or verifiable proof. If your change management process requires an irrefutable record that can be independently verified years down the line without reliance on external, potentially deleted services, then this practice is insufficient.

This approach fails when the intent is to provide direct, actionable evidence rather than a historical marker. For regulated industries, security audits, or compliance requirements, a simple link that will inevitably break offers no real value and could even be detrimental, suggesting a lack of rigorous process. In such cases, a more robust solution for artifact management and retention is paramount.

Furthermore, relying on volatile data can obscure the true purpose of the commit message, which is to explain *why* a change was made. The commit message should focus on the code's intent and logic. When critical process information is tied to ephemeral resources, it can lead to confusion and a breakdown in understanding the evolution of the software, hindering effective automation and future-proofing efforts.

This article draws on Can commit messages include volatile information? and answers to it (1, 2), on the Stack Exchange network, licensed under CC BY-SA 4.0.