# Review a Pull Request in Swift with Atlas in 2026

> Atlas enhances Swift pull request reviews by providing deep context, checking XCTest results, and verifying Swift Package Manager dependencies to catch subtle bugs.

In 2026, Atlas empowers Swift developers to review pull requests by providing comprehensive context beyond simple diffs, integrating directly with your Swift Package Manager projects and leveraging XCTest via swift test for thorough validation. Atlas fetches the branch, reads full changed files, checks signature references, and runs tests, ensuring you catch bugs a line-by-line review might miss.

## Key takeaways

- Atlas provides deep contextual understanding for Swift pull request reviews, going beyond simple diffs.
- Leverage `XCTest via swift test` and `Swift Package Manager` directly within Atlas for comprehensive validation.
- Atlas uses `lsp.findReferences` to proactively catch broken Swift function callers.
- Ensure all instances of Swift constants and feature flags are updated with Atlas's `grep` capabilities.
- Maintain full control over Atlas's actions with permission-gated tool calls and explicit approval for changes to your Swift project.

## How Atlas Fetches and Diffs Swift Code for Pull Request Review

When reviewing a Swift pull request in 2026, Atlas begins by fetching the target branch and generating a unified diff, just as a careful human would. This initial step uses Atlas's robust VCS layer to expose git data, ensuring you always work with the most current code changes for a precise review.

Atlas leverages its integrated VCS layer to interact directly with your git repository, mirroring the actions of a human reviewer. For any Swift pull request, Atlas first fetches the relevant branch, ensuring all local changes are up to date. It then produces a comprehensive diff using the `bash` tool, specifically `git diff`, to identify all modifications. Unlike a simple `git diff` that might only show hunks, Atlas's `diffRaw` capability provides the complete patch, which is crucial for understanding the full scope of changes. This process is permission-gated, meaning Atlas drafts a plan in a read-only plan agent and asks for approval before executing any `bash` commands that modify your local repository state. This ensures transparency and control, allowing you to verify that Atlas is performing the correct `git` operations on your Swift codebase. The `Package.swift` file, a cornerstone of any `Swift Package Manager` project, is often among the files Atlas examines, providing a clear view of any dependency or target changes.

## Gaining Full Context on Swift File Changes

A line-by-line diff often hides critical context, but Atlas addresses this by reading entire Swift files, not just the changed hunks. In 2026, this capability is vital for understanding how a modification in `Sources/MyModule/MyFile.swift` impacts surrounding code, preventing bugs that a limited view would miss.

To catch bugs that a limited diff view would obscure, Atlas employs its `read` tool to pull the full contents of every changed Swift file. This goes beyond the raw patch generated by `git diff`, providing the complete file as it exists on the fetched branch. For instance, if a change modifies a single line within a large Swift function in `Sources/MyApp/Models/User.swift`, Atlas will read the entire `User.swift` file. This allows the agent to analyze the modification within its complete functional and structural context, identifying potential issues that depend on code outside the immediate diff hunks. This deep contextual understanding is particularly important in Swift, where subtle changes in type declarations, access control, or protocol conformances can have far-reaching implications across a module managed by `Swift Package Manager`. Atlas's ability to read full files ensures that the AI agent has the same comprehensive view a human reviewer would gain by opening the file in an IDE.

## Verifying Swift Signature Changes and Callers with Atlas

When a Swift function signature changes, it can silently break callers across your codebase, a risk Atlas mitigates using its `lsp` tool. In 2026, Atlas automatically runs `findReferences` for every modified declaration in files like `Sources/MyLibrary/API.swift`, ensuring no downstream code is inadvertently broken by the pull request.

One of the most insidious bugs in a pull request involves a change to a function or method signature that breaks its callers, especially if those callers are not part of the immediate diff. Atlas addresses this critical review gap using its `lsp` (Language Server Protocol) tool. For every changed function, method, or property declaration within a Swift file, Atlas invokes the `findReferences` operation. This operation, powered by the underlying Swift language server, identifies all locations in the codebase where the modified symbol is used. For example, if a developer changes the signature of `func process(data: Data)` to `func process(payload: Payload)` in `Sources/MyFeature/Processor.swift`, Atlas will use `lsp.findReferences` to locate every call site. If any call site is not updated, Atlas will flag it as a potential issue. This proactive check is vital for maintaining the integrity of large Swift projects managed by `Swift Package Manager`, where a single signature change can have ripple effects across multiple modules and targets.

## Catching Missing Updates with Grep in Swift Codebases

Even with thorough diffs, a pull request might miss updating all instances of a constant or feature flag, a common oversight Atlas catches with its `grep` tool. By 2026, Atlas can efficiently search for old constant names or stale copies across your Swift project, ensuring comprehensive updates in files like `Constants.swift`.

Human reviewers often miss instances where a change should have propagated to multiple locations but did not. This includes updating old constant names, removing stale copies of code, or adjusting feature flags. Atlas employs its `grep` tool to systematically search for such patterns across the entire Swift codebase. For example, if a pull request renames a constant from `oldAPIBaseURL` to `newAPIBaseURL` in `Sources/Shared/Configuration.swift`, Atlas can be instructed to `grep` for `oldAPIBaseURL` to ensure all references have been updated. Similarly, if a feature flag like `isFeatureXEnabled` is being removed, Atlas can `grep` for its usage to confirm it is no longer referenced. This targeted search capability is particularly effective in Swift projects where constants are often defined in dedicated files or structs, such as `struct AppConstants { static let baseURL = "..." }`. The `grep` tool helps Atlas identify these subtle omissions, providing an additional layer of verification beyond what a standard diff or `lsp` check might reveal.

## Running Swift Tests and Reporting Findings

No Swift pull request review is complete without running the tests, a crucial step Atlas automates using `bash` to execute `XCTest via swift test`. In 2026, Atlas will run your entire test suite, including unit and integration tests defined in `Tests/MyModuleTests/`, and report any failures as a prioritized `todowrite` list for immediate action.

The ultimate validation for any code change in Swift is its impact on the existing test suite. Atlas integrates this critical step into its review workflow by using the `bash` tool to execute the `XCTest via swift test` command. This command, the standard for running tests in `Swift Package Manager` projects, compiles and runs all test targets defined in your `Package.swift` file, typically located in directories like `Tests/MyFeatureTests/`. Atlas captures the output of this command, analyzing any test failures or warnings. The findings, including stack traces and error messages from `XCTest`, are then compiled into a `todowrite` list. This list is ordered by severity, presenting the most critical issues first, allowing the developer to quickly address regressions or unexpected behaviors introduced by the pull request. This automated testing ensures that the proposed changes maintain the expected functionality and do not introduce new bugs, providing a robust safety net for Swift development.

## Atlas's Safety and Control Mechanisms for Swift Code Reviews

Atlas prioritizes safety and user control during Swift pull request reviews, employing multiple permission-gated steps. Every Atlas tool call, whether `bash` for `swift test` or `lsp` for `findReferences`, is checked against `allow`, `ask`, and `deny` rules, ensuring you retain full oversight of the AI's actions in 2026.

Atlas is designed with a strong emphasis on safety and user control, particularly crucial when an AI agent interacts with your Swift codebase. Before any tool call is executed, such as running `bash` to execute `swift test` or using `lsp` to `findReferences`, Atlas checks against a set of permission rules: `allow`, `ask`, and `deny`. This means you can configure Atlas to automatically `allow` certain safe operations, `deny` potentially destructive ones, or `ask` for explicit approval for sensitive actions. Furthermore, Atlas operates with a read-only plan agent that drafts a detailed plan of action before switching to a build agent that can execute commands. This plan is surfaced for your review and approval, providing a transparent overview of what Atlas intends to do. All file edits proposed by Atlas are presented as a unified diff, similar to a `git diff`, for your approval before they are written to disk. Atlas also snapshots file changes as `git` patches, allowing for easy diffing and rolling back of any edits. These layered safety mechanisms ensure that you, the Swift developer, remain in complete control throughout the pull request review process.

## Steps

1. 1: Fetch the pull request branch and generate the diff: Atlas uses its VCS layer and the `bash` tool to `git fetch` the target branch and then `git diff` to produce the raw patch for review.
2. 2: Read full Swift files for complete context: Atlas employs the `read` tool to pull the entire content of changed Swift files, such as `Sources/MyModule/Feature.swift`, providing context beyond just the diff hunks.
3. 3: Verify Swift function signature changes with LSP: For every modified function or method in your Swift code, Atlas uses the `lsp` tool's `findReferences` operation to ensure no callers are broken across your `Swift Package Manager` project.
4. 4: Grep for unupdated patterns in Swift files: Atlas utilizes the `grep` tool to search for old constant names, stale code, or feature flags that should have been updated but were missed in files like `Constants.swift`.
5. 5: Run `XCTest` suite and report findings: Atlas executes `XCTest via swift test` using the `bash` tool, capturing test results and compiling any failures into a prioritized `todowrite` list.
6. 6: Review and approve Atlas's proposed changes: Atlas presents all suggested edits as a unified diff for your approval, allowing you to accept or roll back changes before they are written to your Swift codebase.

## FAQ

### How does Atlas integrate with Swift Package Manager projects?

Atlas direct integrates by reading your `Package.swift` file to understand targets, protocols, and dependencies. It can then assist with tasks like adding `XCTest` cases or adopting `async/await` within your `Swift Package Manager` project.

### Can Atlas run my XCTest suite during a pull request review?

Yes, Atlas uses the `bash` tool to execute `XCTest via swift test`, running your entire test suite and reporting any failures as a prioritized `todowrite` list.

### How does Atlas ensure I don't miss broken references after a Swift signature change?

Atlas employs its `lsp` tool to run `findReferences` for every changed function or method signature in your Swift code, identifying and flagging any call sites that were not updated.

### What safety features does Atlas offer when reviewing Swift code?

Atlas provides permission-gated tool calls (`allow`, `ask`, `deny`), drafts plans in a read-only agent, and presents all proposed file edits as a unified diff for your explicit approval before writing to your Swift codebase.

### Can Atlas help me find old constant names or feature flags that should be removed in Swift?

Absolutely. Atlas uses its `grep` tool to search your Swift project for specific patterns, such as old constant names or stale feature flag usages, ensuring comprehensive updates across your codebase.

### Does Atlas only show diff hunks, or does it provide more context for Swift files?

Atlas goes beyond diff hunks. It uses the `read` tool to pull the full contents of changed Swift files, like `Sources/MyModule/MyFile.swift`, giving you complete surrounding context to catch subtle bugs.

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Canonical HTML: https://runatlas.sh/resources/stacks/review-a-pull-request-in-swift
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Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.