Add file-level result caching system with tests

Signed-off-by: Om Ambole <omambole2007@gmail.com>

Author: OmAmbole

src/scancode/cache_manager.py

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+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) nexB Inc. and others. All rights reserved.
+# ScanCode is a trademark of nexB Inc.
+# Visit https://aboutcode.org and https://github.com/aboutcode-org/scancode-toolkit/
+#
+"""
+File-level result caching for faster repeated scans.
+"""
+
+import hashlib
+import json
+import os
+from pathlib import Path
+
+from commoncode import fileutils
+scancode_version = "dev"
+
+class ResultCache:
+    """
+    Manages cached scan results for files based on content hash.
+    """
+    
+    def __init__(self, cache_dir=None):
+        """
+        Initialize cache manager.
+        
+        Args:
+            cache_dir: Custom cache directory path. If None, uses default.
+        """
+        if cache_dir:
+            self.cache_dir = Path(cache_dir)
+        else:
+            # Use platform-appropriate cache directory
+            cache_base = Path.home() / '.cache' / 'scancode'
+            self.cache_dir = cache_base / 'file_results'
+        
+        self.cache_dir.mkdir(parents=True, exist_ok=True)
+        self.stats = {'hits': 0, 'misses': 0}
+    
+    def _get_file_hash(self, file_path, scan_options):
+        """
+        Generate unique hash for file + scan configuration.
+        
+        Args:
+            file_path: Path to file being scanned
+            scan_options: Dict of enabled scan options (e.g., {'license': True})
+        
+        Returns:
+            SHA256 hex digest string
+        """
+        hasher = hashlib.sha256()
+        
+        # Hash file content
+        with open(file_path, 'rb') as f:
+            hasher.update(f.read())
+        
+        # Hash scan configuration to invalidate on option changes
+        config_str = f"{scancode_version}:{sorted(scan_options.items())}"
+        hasher.update(config_str.encode('utf-8'))
+        
+        return hasher.hexdigest()
+    
+    def get_cached_result(self, file_path, scan_options):
+        """
+        Retrieve cached scan result if available.
+        
+        Args:
+            file_path: Path to file
+            scan_options: Dict of scan options
+        
+        Returns:
+            Dict with scan results or None if not cached
+        """
+        file_hash = self._get_file_hash(file_path, scan_options)
+        cache_file = self.cache_dir / f"{file_hash}.json"
+        
+        if cache_file.exists():
+            try:
+                with open(cache_file, 'r') as f:
+                    self.stats['hits'] += 1
+                    return json.load(f)
+            except (json.JSONDecodeError, IOError):
+                # Corrupted cache, remove it
+                cache_file.unlink(missing_ok=True)
+                self.stats['misses'] += 1
+                return None
+        
+        self.stats['misses'] += 1
+        return None
+    
+    def store_result(self, file_path, scan_options, result):
+        """
+        Store scan result in cache.
+        
+        Args:
+            file_path: Path to scanned file
+            scan_options: Dict of scan options used
+            result: Scan result dict to cache
+        """
+        file_hash = self._get_file_hash(file_path, scan_options)
+        cache_file = self.cache_dir / f"{file_hash}.json"
+        
+        try:
+            with open(cache_file, 'w') as f:
+                json.dump(result, f)
+        except IOError as e:
+            # Don't fail scan if cache write fails
+            print(f"Warning: Failed to write cache: {e}")
+    
+    def clear_cache(self):
+        """Remove all cached result files."""
+        for file in self.cache_dir.glob("*.json"):
+            try:
+                file.unlink()
+            except Exception:
+                pass
+    
+    def get_stats(self):
+        """Return cache statistics."""
+        total = self.stats['hits'] + self.stats['misses']
+        hit_rate = (self.stats['hits'] / total * 100) if total > 0 else 0
+        return {
+            'hits': self.stats['hits'],
+            'misses': self.stats['misses'],
+            'hit_rate_percent': round(hit_rate, 1)
+        }

src/scancode/plugin_cache.py

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+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) nexB Inc. and others. All rights reserved.
+#
+"""
+CLI plugin to enable result caching.
+"""
+
+import click
+
+from plugincode.scan import ScanPlugin
+from plugincode.scan import scan_impl
+from scancode.cache_manager import ResultCache
+
+
+@scan_impl
+class CachePlugin(ScanPlugin):
+    """
+    Enable file-level result caching for faster repeated scans.
+    """
+    
+    options = [
+        click.Option(
+            ['--cache'],
+            is_flag=True,
+            default=False,
+            help='Enable result caching for faster repeated scans.',
+        ),
+        click.Option(
+            ['--cache-dir'],
+            type=click.Path(exists=False, file_okay=False, dir_okay=True),
+            metavar='DIR',
+            help='Custom directory for cache storage. '
+                 'Default: ~/.cache/scancode/file_results',
+        ),
+        click.Option(
+            ['--force-reindex'],
+            is_flag=True,
+            default=False,
+            help='Ignore cache and perform full rescan of all files.',
+        ),
+    ]
+    
+    def is_enabled(self, cache, **kwargs):
+        return cache
+    
+    def setup(self, **kwargs):
+        """
+        Initialize cache manager for the scan.
+        """
+        pass
+
+
+def get_cache_manager(cache, cache_dir, **kwargs):
+    """
+    Factory function to get cache manager instance.
+    
+    Args:
+        cache: Boolean, whether caching is enabled
+        cache_dir: Custom cache directory path
+    
+    Returns:
+        ResultCache instance or None if caching disabled
+    """
+    if not cache:
+        return None
+    
+    return ResultCache(cache_dir=cache_dir)

tests/scancode/test_cache_manager.py

@@ -0,0 +1,115 @@
+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) nexB Inc. and others. All rights reserved.
+#
+"""
+Tests for result caching functionality.
+"""
+
+import json
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from scancode.cache_manager import ResultCache
+
+
+class TestResultCache:
+    
+    def test_cache_stores_and_retrieves_results(self):
+        """Test basic cache store and retrieval."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            cache = ResultCache(cache_dir=tmpdir)
+            
+            # Create a test file
+            test_file = Path(tmpdir) / 'test.py'
+            test_file.write_text('# Test file\nprint("hello")')
+            
+            scan_options = {'license': True, 'copyright': False}
+            result = {'licenses': ['MIT'], 'path': str(test_file)}
+            
+            # Store result
+            cache.store_result(test_file, scan_options, result)
+            
+            # Retrieve result
+            cached = cache.get_cached_result(test_file, scan_options)
+            
+            assert cached is not None
+            assert cached['licenses'] == ['MIT']
+            assert cache.stats['hits'] == 1
+    
+    def test_cache_miss_on_file_change(self):
+        """Test cache invalidation when file content changes."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            cache = ResultCache(cache_dir=tmpdir)
+            test_file = Path(tmpdir) / 'test.py'
+            
+            # First content and scan
+            test_file.write_text('# Version 1')
+            scan_options = {'license': True}
+            result1 = {'version': 1}
+            cache.store_result(test_file, scan_options, result1)
+            
+            # Modify file
+            test_file.write_text('# Version 2')
+            
+            # Should be cache miss
+            cached = cache.get_cached_result(test_file, scan_options)
+            assert cached is None
+            assert cache.stats['misses'] == 1
+    
+    def test_cache_miss_on_scan_options_change(self):
+        """Test cache invalidation when scan options change."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            cache = ResultCache(cache_dir=tmpdir)
+            test_file = Path(tmpdir) / 'test.py'
+            test_file.write_text('# Test')
+            
+            # First scan with license
+            options1 = {'license': True}
+            cache.store_result(test_file, options1, {'result': 1})
+            
+            # Second scan with copyright added
+            options2 = {'license': True, 'copyright': True}
+            cached = cache.get_cached_result(test_file, options2)
+            
+            assert cached is None  # Should miss due to different options
+    
+    def test_cache_statistics(self):
+        """Test cache statistics tracking."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            cache = ResultCache(cache_dir=tmpdir)
+            test_file = Path(tmpdir) / 'test.py'
+            test_file.write_text('# Test')
+            
+            options = {'license': True}
+            
+            # First scan: miss
+            cache.get_cached_result(test_file, options)
+            
+            # Store and retrieve: hit
+            cache.store_result(test_file, options, {'data': 'test'})
+            cache.get_cached_result(test_file, options)
+            
+            stats = cache.get_stats()
+            assert stats['hits'] == 1
+            assert stats['misses'] == 1
+            assert stats['hit_rate_percent'] == 50.0
+    
+    def test_clear_cache(self):
+        """Test cache clearing functionality."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            cache = ResultCache(cache_dir=tmpdir)
+            test_file = Path(tmpdir) / 'test.py'
+            test_file.write_text('# Test')
+            
+            options = {'license': True}
+            cache.store_result(test_file, options, {'data': 'test'})
+            
+            # Clear cache
+            cache.clear_cache()
+            
+            # Should be miss after clear
+            cached = cache.get_cached_result(test_file, options)
+            assert cached is None