[Refactor] Extract diff parsing into src/diff module

[Copilot]

• Analyze current codebase structure and understand what needs to be extracted
• Verify current build and test status (all tests passing)
• Identify code to move from src/hook.rs (traits: FilePath, Utf8String, DiffDeltaPath)
• Identify code to move from src/multi_step_integration.rs (ParsedFile struct, parse_diff function, extract_file_path_from_diff_parts function, and tests)
• Create src/diff/ module structure with mod.rs, parser.rs, traits.rs
• Move diff parsing logic from multi_step_integration.rs to parser.rs
• Move utility traits from hook.rs to traits.rs
• Update lib.rs to expose new diff module
• Update imports in hook.rs and multi_step_integration.rs
• Remove moved code from original files
• Fix import issues in examples and tests
• Verify all tests pass and code builds (9 unit tests + 53 integration tests passing)
• Verify hook.rs line count reduction (632 → 565 lines, 67 line reduction)
• All diff parsing tests moved to new module and still passing
• Created clean module separation between diff processing and hook logic
• Fixed CI clippy warnings - Removed needless borrows in model validation test

Verification Results

✅ Module Structure: src/diff/ created with mod.rs, parser.rs, traits.rs
✅ Code Movement: All diff parsing logic successfully extracted from multi_step_integration.rs
✅ Trait Extraction: FilePath, Utf8String, DiffDeltaPath moved from hook.rs to diff/traits.rs
✅ Import Updates: All affected files updated to use new module structure
✅ Tests: All 4 parse_diff tests moved to new module, all tests still pass (9 unit + 53 integration)
✅ Build: Project builds successfully with no compilation errors
✅ Size Reduction: hook.rs reduced from 632 to 565 lines (67 line reduction)
✅ Functionality: All existing functionality preserved, clean module boundaries established
✅ CI Fix: Clippy warnings resolved by removing needless borrows in test code

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Refactor] Extract diff parsing into src/diff module</issue_title>
<issue_description>## Context
src/hook.rs is 725 lines and mixes multiple concerns. This extracts diff parsing into a dedicated module as the first step in breaking it apart.

Priority

🟡 HIGH - Reduces large file, improves organization

Steps

1. Create module structure

mkdir -p src/diff
touch src/diff/mod.rs
touch src/diff/parser.rs
touch src/diff/traits.rs

2. Create src/diff/traits.rs

Extract utility traits from hook.rs:

//! Utility traits for diff processing.

use std::path::PathBuf;
use anyhow::Result;

/// Extension trait for PathBuf to support file operations needed for commits
pub trait FilePath {
    fn is_empty(&self) -> Result<bool>;
    fn write(&self, msg: String) -> Result<()>;
    fn read(&self) -> Result<String>;
}

// Move implementations from hook.rs lines 88-109

/// Extension trait for converting bytes to UTF-8 strings
pub trait Utf8String {
    fn to_utf8(&self) -> String;
}

// Move implementations from hook.rs lines 128-152

/// Extension trait for git2::DiffDelta to get file paths
pub trait DiffDeltaPath {
    fn path(&self) -> PathBuf;
}

// Move implementations from hook.rs lines 112-125

3. Create src/diff/parser.rs

Extract diff parsing logic from multi_step_integration.rs:

//! Git diff parsing utilities.

use std::path::PathBuf;
use anyhow::Result;

/// Represents a parsed file from a git diff
#[derive(Debug, Clone)]
pub struct ParsedFile {
    pub path: String,
    pub operation: String,
    pub diff_content: String,
}

/// Parse git diff into individual file changes.
///
/// Handles various diff formats including:
/// - Standard git diff output
/// - Diffs with commit hashes
/// - Diffs with various path prefixes (a/, b/, c/, i/)
/// - Deleted files (/dev/null paths)
///
/// # Arguments
/// * `diff_content` - Raw git diff text
///
/// # Returns
/// * `Result<Vec<ParsedFile>>` - Parsed files or error
pub fn parse_diff(diff_content: &str) -> Result<Vec<ParsedFile>> {
    // Move implementation from multi_step_integration.rs lines 212-402
}

/// Extracts file path from diff header parts
fn extract_file_path_from_diff_parts(parts: &[&str]) -> Option<String> {
    // Move from multi_step_integration.rs lines 186-209
}

#[cfg(test)]
mod tests {
    // Move tests from multi_step_integration.rs lines 639-810
}

4. Create src/diff/mod.rs

//! Diff processing and parsing utilities.
//!
//! This module handles parsing git diffs into structured data
//! and provides utilities for working with diff content.

pub mod parser;
pub mod traits;

pub use parser::{ParsedFile, parse_diff};
pub use traits::{FilePath, Utf8String, DiffDeltaPath};

5. Update src/lib.rs

pub mod diff;

6. Update imports in affected files

In src/hook.rs:

// Add at top
use crate::diff::traits::{FilePath, Utf8String, DiffDeltaPath};

// Remove old trait definitions (lines 88-152)

In src/multi_step_integration.rs:

// Add at top
use crate::diff::parser::parse_diff;

// Remove parse_diff function and helpers (lines 186-402)
// Keep the call sites

7. Remove moved code from original files

Delete the code that was moved to avoid duplication.

Verification Criteria

✅ Pass:

• src/diff/ module exists with mod.rs, parser.rs, traits.rs
• All diff parsing logic moved from multi_step_integration.rs
• All utility traits moved from hook.rs
• No duplicate code remains in original files
• All imports updated correctly
• cargo build succeeds
• cargo test passes all tests
• All existing diff parsing tests still pass
• cargo clippy shows no warnings
• hook.rs reduced in size (should be ~600 lines)

Test manually

# Run the diff parsing tests specifically
cargo test --test multi_step -- parse_diff

# Test with actual git repo
cd test-repo
echo "test" > test.txt
git add test.txt
# Trigger hook to test parsing
git commit --no-edit

Estimated Time

4-5 hours

Dependencies

• Issue Allow for git-ai hook reinstall #3 (Standardize type names)

Labels

• refactor
• module-structure
• diff-processing</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #66

---

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[oleander]

@copilot Fix broken CI

[Copilot]

@copilot Fix broken CI

Fixed clippy warnings causing CI failure by removing needless borrows in model validation tests. Commit 8410a2a.

[Copilot]

Pull Request Overview

Refactor extracting diff parsing and related utility traits into a dedicated src/diff module to improve separation of concerns and reduce hook.rs size.

• Created diff module (parser.rs, traits.rs, mod.rs) and moved parsing logic and utility traits.
• Updated imports across codebase (examples, tests, integration module) to use new module structure.
• Minor cleanup in tests (removed needless borrows) and added re-exports in diff/mod.rs for cleaner public API.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/diff/parser.rs	New module containing extracted parse_diff logic and ParsedFile struct.
src/diff/traits.rs	New module containing FilePath, DiffDeltaPath, and Utf8String traits and implementations.
src/diff/mod.rs	Module aggregator re-exporting parser and traits for external use.
src/multi_step_integration.rs	Removed inlined parsing logic; now imports parse_diff and ParsedFile.
src/hook.rs	Removed trait definitions; now imports traits from diff module.
src/lib.rs	Exposes new diff module publicly.
examples/multi_step_commit.rs	Updated to import parse_diff from new module (currently via internal submodule path).
tests/patch_test.rs	Updated imports to use traits from new diff module.
tests/model_validation_test.rs	Removed unnecessary borrows (clippy cleanup).

[Copilot]

[nitpick] Since diff::mod.rs re-exports parse_diff, prefer use ai::diff::parse_diff; to decouple the example from internal module structure and rely on the intended public API surface.

Suggested change

	use ai::diff::parser::parse_diff;
	use ai::diff::parse_diff;

[oleander]

@copilot Implement review request comments

[oleander]

@copilot Fix review comments

[Copilot]

@copilot Fix review comments

I still don't have access to the specific review comments that need to be fixed. Could you please share the specific feedback or review comments that need to be addressed? I'm ready to implement the changes once I know what needs to be fixed.

[oleander]

@copilot Fix review comments

[Copilot]

Pull Request Overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

[Copilot]

Removing parse_diff (and ParsedFile) from this module without providing a re-export is a breaking API change for users previously calling crate::multi_step_integration::parse_diff. Consider adding a deprecated pub use parse_diff; here (or in this module) to preserve backward compatibility, or document the breaking change.

Suggested change

	#[deprecated(note = "Use crate::diff::parser::{parse_diff, ParsedFile} instead")]
	pub use crate::diff::parser::{parse_diff, ParsedFile};

[Copilot]

The variable _commit_hash_line is collected but never used; since it has no effect on parsing, it can be removed to reduce noise, or its intended purpose (e.g., future conditional logic) should be implemented.

Suggested change

	let mut _commit_hash_line: Option<&str> = None;
	// First scan to detect if this is a commit message with hash
	for line in diff_content.lines().take(3) {
	if line.len() >= 40 && line.chars().take(40).all(|c| c.is_ascii_hexdigit()) {
	_commit_hash_line = Some(line);
	break;
	}
	}

[oleander]

@copilot Fix review comments

[oleander]

@copilot Fix review comments