Add function coverage support to go-covercheck

[Copilot]

This PR adds comprehensive function coverage support to go-covercheck, enabling users to track and enforce coverage thresholds at the function level alongside existing statement and block coverage.

Features Added

Function Coverage Tracking

• Function counting: Uses Go AST parsing to accurately count function declarations in source files
• Coverage calculation: Matches functions with coverage profile data to determine covered vs uncovered functions
• Aggregation: Shows function coverage per file, per package, and total across the entire project

CLI Integration

New command-line flags for function coverage:

• --function-threshold (-n): Set global function coverage threshold (default: 60%)
• --total-function-threshold (-F): Override total function coverage threshold
• --sort-by functions: Sort results by function hit count
• --sort-by function-percent: Sort results by function coverage percentage

Configuration File Support

Function thresholds can be configured in .go-covercheck.yml:

functionThreshold: 60.0
total:
  functions: 80.0
perFile:
  functions:
    main.go: 0
perPackage:
  functions:
    pkg/config: 90

Enhanced Output

All output formats now include function coverage:

• Table format: New "Functions" column showing coverage like 8/12 (66.7%)
• JSON/YAML: Include functionCoverage, functionPercentage, and functionThreshold fields
• Export formats: CSV, TSV, Markdown, and HTML all include function data
• Failure reporting: Function coverage failures shown with [F] prefix in summary

History and Compare Support

• History display: Function coverage shown in history table with [F] indicator
• History comparison: Function coverage deltas displayed when comparing against previous commits
• Complete integration: All history operations now include function coverage data

Example Output

┌─────────────────┬─────────────┬───────────┬─────────────┬─────────────┬───────────┬─────────────┐
│                 │ STATEMENTS  │  BLOCKS   │ FUNCTIONS   │ STATEMENT % │  BLOCK %  │ FUNCTION %  │
├─────────────────┼─────────────┼───────────┼─────────────┼─────────────┼───────────┼─────────────┤
│ pkg/config.go   │     47/55   │   32/40   │     5/6     │      85.5   │     80.0  │      83.3   │
│ pkg/compute.go  │    102/104  │   53/55   │     5/7     │      98.1   │     96.4  │      71.4   │
├─────────────────┼─────────────┼───────────┼─────────────┼─────────────┼───────────┼─────────────┤
│ BY TOTAL        │   629/731   │  378/462  │    64/73    │      86.0   │     81.8  │      87.7   │
└─────────────────┴─────────────┴───────────┴─────────────┴─────────────┴───────────┴─────────────┘

Technical Implementation

• AST parsing: Uses go/ast package to parse Go source files and count function declarations
• Coverage matching: Correlates function line ranges with coverage profile blocks to determine coverage status
• Method support: Handles both regular functions and methods (functions with receivers)
• Error handling: Gracefully handles missing source files and parsing errors
• Minimal changes: Follows existing code patterns to maintain consistency

Testing

• All existing tests continue to pass
• Added comprehensive tests for function counting and coverage matching logic
• Updated model tests to include new function-related fields
• Updated history tests to include function coverage expectations
• Verified functionality with real coverage data

This implementation provides complete function coverage analysis with full feature parity to the existing statement and block coverage functionality.

Fixes #40.

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[mach6]

History and compare history should also work for func coverage

[Copilot]

History and compare history should also work for func coverage

Function coverage support has been added to history and compare history functionality. This includes:

• History display now shows function coverage with [F] indicator alongside statements [S] and blocks [B]
• History comparison shows function coverage deltas when comparing against previous commits
• All existing history operations now include function coverage data

The changes are implemented in commit a36f473 with updated tests to verify the functionality works correctly.