fix: set nil value error

[kooksee]

Summary by CodeRabbit

• Refactor

  • Enhanced error handling in struct field injection for Interface, Pointer, Function, Map, and Slice field types to ensure proper validation before field assignment.

• Chores

  • Updated dependency management in module configuration.
  • Added new example program demonstrating a complete dependency injection setup with nested struct relationships and constructor registration.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The pull request refactors error handling in field injection within the DI library by retrieving values into local variables before setting struct fields. A module dependency transitions from indirect to direct, and a new example program demonstrates the DI framework with multiple struct types and constructors.

Changes

Cohort / File(s)	Change Summary
Core DI Field Injection Refactor dixinternal/dix.go	Modified field injection logic for Interface, Ptr, Func, Map, and Slice-typed fields. Changed from directly setting fields with UnwrapErr(&r) to retrieving values into a local variable val, checking errors, then setting with vp.Field(i).Set(val).
Example Module Dependencies example/go.mod	Transitioned github.com/kr/pretty v0.3.1 from an indirect to a direct dependency in the require block.
New Example Program example/nildata/main.go	Added new program demonstrating DIX global DI setup. Defines structs (AP, A, A1, AR, BP, B, BR), interface (BI), constructors (newA, newB), and a params struct with dependency injection via dixglobal.Provide and recovery handling.

Sequence Diagram

sequenceDiagram
    participant injectStruct
    participant field as Field (Interface/Ptr/Func/Map/Slice)
    
    rect rgb(100, 150, 100)
    Note over injectStruct,field: New Flow (After)
    injectStruct->>field: Retrieve value from container
    field-->>injectStruct: Return value & error
    injectStruct->>injectStruct: Check for errors
    alt Error found
        injectStruct->>injectStruct: Handle error
    else No error
        injectStruct->>field: Set field value
        field-->>injectStruct: Success
    end
    end
    
    rect rgb(150, 100, 100)
    Note over injectStruct,field: Old Flow (Before)
    injectStruct->>field: Retrieve & set in one step
    field-->>injectStruct: Field set with UnwrapErr result
    end

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

• The field injection refactor is a consistent pattern applied uniformly across five field kinds, reducing cognitive load
• The go.mod change is straightforward dependency management
• The new example program is self-contained and demonstrates existing framework functionality
• Focus areas: Verify error handling is correct in the new flow for all five field types; confirm the dependency change doesn't introduce unexpected transitive dependencies

Poem

🐰 With gentle paws, we catch the errors true,
Before we set the fields in morning dew,
From indirect to direct, dependencies align,
New examples bloom—the DI framework shines!
✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: set nil value error' directly relates to the main changes in the PR, which refactor how nil/error values are handled in field injection.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/nil_value

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[gemini-code-assist]

Summary of Changes

Hello @kooksee, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily focuses on enhancing the robustness of the dependency injection mechanism by addressing potential 'nil value error' issues. The core change involves a more explicit error handling flow within the injectStruct function, ensuring that value assignments only proceed if no errors occurred during value retrieval. To validate or demonstrate this improvement, a new example has been added, showcasing the injection process with different data structures. Additionally, a minor dependency declaration update was made in the example module.

Highlights

• Error Handling Refinement: The injectStruct method in dixinternal/dix.go has been refactored to explicitly check for errors immediately after retrieving a value using getValue. This prevents attempting to assign a potentially nil or invalid value if an error occurred during its resolution, thereby fixing 'nil value error' scenarios.
• New Example Added: A new example file, example/nildata/main.go, has been introduced. This example demonstrates the usage of dixglobal.Inject with various struct and interface types, likely serving as a test case or demonstration for the improved error handling.
• Dependency Update: The example/go.mod file was updated to move github.com/kr/pretty from an indirect dependency to a direct requirement, indicating its direct usage within the example module.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a potential panic in the dependency injection logic. By checking for an error before attempting to set a field's value via reflection, it prevents a crash when a provider fails to yield a value. The addition of the nildata example is a good way to demonstrate and test this fix. I have one suggestion regarding code duplication that was introduced with the fix, which could improve maintainability.

[Copilot]

Pull request overview

This PR fixes an issue with setting nil values during dependency injection by refactoring the field-setting logic in the injectStruct method. The key change separates the retrieval of dependency values from their assignment to struct fields, ensuring that nil value errors are properly caught before attempting to set field values.

Key Changes:

• Refactored injectStruct to use intermediate variables for retrieved values before calling Set()
• Added a new example demonstrating nil value handling in the dependency injection system
• Updated dependencies in go.mod to make github.com/kr/pretty a direct dependency

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
dixinternal/dix.go	Refactored field setting logic to prevent nil value errors by checking errors before calling Set() on reflect.Value
example/nildata/main.go	Added new example demonstrating dependency injection with nil interface values
example/go.mod	Moved kr/pretty from indirect to direct dependency
go.work.sum	Updated workspace checksums (auto-generated)

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[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between a1f4608 and 0aead80.

⛔ Files ignored due to path filters (1)

• go.work.sum is excluded by !**/*.sum

📒 Files selected for processing (3)

• dixinternal/dix.go (1 hunks)
• example/go.mod (1 hunks)
• example/nildata/main.go (1 hunks)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: CodeQL analysis (go)
• GitHub Check: Agent

🔇 Additional comments (5)

dixinternal/dix.go (3)

304-309: LGTM! Critical bug fix for Interface/Ptr/Func fields.

The refactoring correctly ensures the value is retrieved and error-checked before calling Set, preventing invalid or nil values from being assigned to fields when getValue fails.

---

317-322: LGTM! Critical bug fix for Map fields.

The same fix pattern is correctly applied: retrieve the value, check for errors, then set the field. This prevents the field from being assigned an invalid value when dependency resolution fails.

---

324-329: LGTM! Critical bug fix for Slice fields.

The fix is consistently applied across all field types in injectStruct, ensuring errors are caught before any field modifications occur.

example/go.mod (1)

8-8: LGTM! Dependency correctly promoted to direct.

The kr/pretty dependency is now directly used in example/nildata/main.go, so promoting it from indirect to direct is appropriate.

example/nildata/main.go (1)

43-45: Clarify intent: Constructor returns zero-initialized struct.

The newB constructor returns BR{} with an uninitialized BI field (nil). If this is intentional to demonstrate the nil value handling fix, consider adding a comment. Otherwise, this may cause issues in the DI resolution.

Is the nil BI field intentional for testing purposes? If so, please add a comment explaining this is a test case for nil value handling. If not, the constructor should initialize the field:

func newB(p BP) BR {
	return BR{BI: someValue} // Initialize BI field
}