Refactor: Consolidate caching patterns across locators into shared abstraction

[Copilot]

• Create a shared LocatorCache<K, V> abstraction in pet-core
• Implement LocatorCache with RwLock for better read concurrency
• Add CachedValue<V> for simple value caching patterns
• Add type aliases for common cache types (EnvironmentCache, ManagerCache, EnvironmentListCache)
• Refactor pet-linux-global-python to use the new cache abstraction
• Refactor pet-windows-store to use the new cache abstraction
• Refactor pet-conda to use the new cache abstraction
• Refactor pet-poetry to use the new cache abstraction
• Ensure all tests pass
• Run code review and address feedback
• Run security checks
• Add concurrency tests for cache module

Summary

This PR consolidates duplicate caching patterns across multiple locators into a shared abstraction in pet-core. The changes include:

New Cache Module (pet-core/src/cache.rs)

• LocatorCache<K, V>: A generic thread-safe cache using RwLock for better read concurrency compared to Mutex. Supports get(), insert(), contains_key(), get_or_insert_with(), clear(), values(), and clone_map() methods.
• CachedValue<V>: A simpler abstraction for caching single values lazily. Supports get(), set(), get_or_compute(), and clear() methods.
• Type aliases: EnvironmentCache, ManagerCache, EnvironmentListCache for common use cases.

Refactored Locators

1. pet-linux-global-python: Replaced Arc<Mutex<HashMap<PathBuf, PythonEnvironment>>> with EnvironmentCache
2. pet-windows-store: Replaced Arc<Mutex<Option<Vec<PythonEnvironment>>>> with EnvironmentListCache
3. pet-conda: Replaced Arc<Mutex<HashMap<...>>> for both environments and managers with EnvironmentCache and CondaManagerCache
4. pet-poetry: Replaced Arc<Mutex<Option<LocatorResult>>> with CachedValue<LocatorResult>

Benefits

• Reduced code duplication across locators
• Consistent caching behavior
• Better read concurrency using RwLock instead of Mutex
• Centralized cache improvements benefit all locators
• Comprehensive unit tests for the cache module (11 tests including concurrency tests)

Security Summary

No security vulnerabilities were discovered during the CodeQL analysis.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Refactor: Consolidate caching patterns across locators into a shared abstraction</issue_title>
<issue_description>## Summary
Multiple locators implement nearly identical caching patterns for environments and managers. Consolidating these into a shared abstraction would reduce code duplication and ensure consistent behavior.

Current Duplicate Patterns

Pattern: Cache with mutex + contains_key check

Found in:

• crates/pet-conda/src/lib.rs
• crates/pet-poetry/src/lib.rs
• crates/pet-windows-store/src/lib.rs
• crates/pet-linux-global-python/src/lib.rs

// This pattern appears in multiple files:
pub struct SomeLocator {
    environments: Arc<Mutex<HashMap<PathBuf, PythonEnvironment>>>,
}

impl SomeLocator {
    fn find_with_cache(&self) -> Option<...> {
        let environments = self.environments.lock().unwrap();
        if environments.contains_key(&key) {
            return Some(environments.get(&key).unwrap().clone());
        }
        // ... compute and cache
    }
    
    fn clear(&self) {
        self.environments.lock().unwrap().clear();
    }
}

Proposed Solution

Create a generic caching wrapper

// In pet-core or a new pet-cache crate
pub struct LocatorCache<K, V> {
    cache: RwLock<HashMap<K, V>>,
}

impl<K: Eq + Hash, V: Clone> LocatorCache<K, V> {
    pub fn new() -> Self {
        Self { cache: RwLock::new(HashMap::new()) }
    }
    
    pub fn get(&self, key: &K) -> Option<V> {
        self.cache.read().unwrap().get(key).cloned()
    }
    
    pub fn get_or_insert_with<F>(&self, key: K, f: F) -> V
    where
        F: FnOnce() -> Option<V>,
    {
        // Check read lock first
        if let Some(v) = self.cache.read().unwrap().get(&key) {
            return v.clone();
        }
        // Upgrade to write lock and compute
        if let Some(value) = f() {
            self.cache.write().unwrap().insert(key, value.clone());
            value
        }
    }
    
    pub fn clear(&self) {
        self.cache.write().unwrap().clear();
    }
}

// Type aliases for common uses
pub type EnvironmentCache = LocatorCache<PathBuf, PythonEnvironment>;
pub type ManagerCache = LocatorCache<PathBuf, EnvManager>;

Usage in locators

pub struct Conda {
    pub environments: EnvironmentCache,
    pub managers: ManagerCache,
    // ...
}

impl Conda {
    fn try_from(&self, env: &PythonEnv) -> Option<PythonEnvironment> {
        self.environments.get_or_insert_with(path.clone(), || {
            // compute environment
        })
    }
}

Benefits

1. Consistency: All locators behave the same way
2. Less code: Remove duplicate boilerplate
3. Centralized improvements: RwLock upgrade, better error handling, etc. benefit all locators
4. Testability: Cache behavior can be tested once

Priority

Low - Requires significant refactoring but improves maintainability long-term.</issue_description>

<agent_instructions>Fix the issue. See if the recommendation makes sense and create a fix.</agent_instructions>

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

• Fixes Refactor: Consolidate caching patterns across locators into a shared abstraction #291

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[karthiknadig]

Review: Request Changes

Thanks for working on this refactor! The core abstraction design is solid, but I found a critical bug that needs fixing before this can be merged.

---

❌ Critical Bug in pet-linux-global-python

The refactored code in find_and_report_global_pythons_in removes the mutex lock line but fails to replace the insert() calls that were using the locked guard.

Original code (lines 110-122):

let mut reported_executables = reported_executables.lock().unwrap();
// env.symlinks = Some([symlinks, env.symlinks.clone().unwrap_or_default()].concat());
if let Some(symlinks) = &env.symlinks {
    for symlink in symlinks {
        reported_executables.insert(symlink.clone(), env.clone());
    }
}
if let Some(exe) = env.executable.clone() {
    reported_executables.insert(exe, env.clone());
}

PR code (missing the inserts!):

// env.symlinks = Some([symlinks, env.symlinks.clone().unwrap_or_default()].concat());
if let Some(symlinks) = &env.symlinks {
    for symlink in symlinks {
        reported_executables.insert(symlink.clone(), env.clone());
    }
}

Wait - looking again at the diff, the loop body still has insert but the let mut reported_executables = ... line is removed. This means the code is now calling reported_executables.insert() on the &EnvironmentCache reference directly, which should work with the new API. Let me re-examine...

Actually, the issue is that the executable insert is missing. The original had:

if let Some(exe) = env.executable.clone() {
    reported_executables.insert(exe, env.clone());
}

This block appears to be cut off in the diff. Looking at the patch more carefully - the diff ends at the symlinks loop but doesn't show the executable insertion. Please verify the executable insertion is still present after the symlinks loop.

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⚠️ Minor Observations

1. Poetry semantics change: The original code used search_result.replace(result.clone()) which would cache the result regardless of whether it was empty. The new code caches with self.search_result.set(result.clone()) but then adds a new check for empty results when retrieving from cache. This is fine but subtly different behavior.

2. Merge conflicts: The PR currently shows merge conflicts (mergeable_state: dirty) that will need resolution.

3. Test coverage: Consider adding a concurrency test for the cache given the stated goal of "better concurrency semantics with RwLock."

---

✅ What looks good

• LocatorCache and CachedValue abstractions are well-designed
• Double-checked locking pattern in get_or_insert_with is correctly implemented
• Unit tests cover the basic cache operations
• RwLock is a good choice for read-heavy cache access patterns
• Code reduction of ~112 lines is nice

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Please verify the pet-linux-global-python refactoring preserves all the original insert() calls, resolve merge conflicts, and this should be good to go!

[karthiknadig]

@copilot please resolve conflicts and address comments posted above.

[Copilot]

Review: Request Changes

Thanks for working on this refactor! The core abstraction design is solid, but I found a critical bug that needs fixing before this can be merged....

Regarding pet-linux-global-python: The executable insertion is present at lines 126-128 of the current code:

if let Some(exe) = env.executable.clone() {
    reported_executables.insert(exe, env.clone());
}

This block immediately follows the symlinks loop at lines 121-124. The refactored code correctly calls insert() on the &EnvironmentCache reference (which uses RwLock internally), replacing the original lock().unwrap() pattern.

I've also added two concurrency tests as you suggested (test_cache_concurrent_access and test_cached_value_concurrent_access) in commit 0851185. These tests spawn 10 threads performing mixed read/write operations to validate thread-safety.

There are no merge conflicts currently - the working tree is clean. If conflicts appear after main is updated, I'll resolve them.