From cd61e922ff312eefe0be55b7b468b83117f94181 Mon Sep 17 00:00:00 2001
From: Sergei Zimmerman <xokdvium@proton.me>
Date: Wed, 14 May 2025 21:42:35 +0000
Subject: [PATCH] libutil: Use heterogeneous lookup for LRUCache

This gets rid of some ugly std::string_view -> std::string
conversions, which are an eye-sore and lead to extra copying.
---
 src/libstore/store-api.cc                 | 10 +++++-----
 src/libutil/include/nix/util/lru-cache.hh | 13 ++++++++-----
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 08c542041..f20d2d329 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -570,7 +570,7 @@ bool Store::isValidPath(const StorePath & storePath)
 {
     {
         auto state_(state.lock());
-        auto res = state_->pathInfoCache.get(std::string(storePath.to_string()));
+        auto res = state_->pathInfoCache.get(storePath.to_string());
         if (res && res->isKnownNow()) {
             stats.narInfoReadAverted++;
             return res->didExist();
@@ -582,7 +582,7 @@ bool Store::isValidPath(const StorePath & storePath)
         if (res.first != NarInfoDiskCache::oUnknown) {
             stats.narInfoReadAverted++;
             auto state_(state.lock());
-            state_->pathInfoCache.upsert(std::string(storePath.to_string()),
+            state_->pathInfoCache.upsert(storePath.to_string(),
                 res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue { .value = res.second });
             return res.first == NarInfoDiskCache::oValid;
         }
@@ -641,7 +641,7 @@ std::optional<std::shared_ptr<const ValidPathInfo>> Store::queryPathInfoFromClie
     auto hashPart = std::string(storePath.hashPart());
 
     {
-        auto res = state.lock()->pathInfoCache.get(std::string(storePath.to_string()));
+        auto res = state.lock()->pathInfoCache.get(storePath.to_string());
         if (res && res->isKnownNow()) {
             stats.narInfoReadAverted++;
             if (res->didExist())
@@ -657,7 +657,7 @@ std::optional<std::shared_ptr<const ValidPathInfo>> Store::queryPathInfoFromClie
             stats.narInfoReadAverted++;
             {
                 auto state_(state.lock());
-                state_->pathInfoCache.upsert(std::string(storePath.to_string()),
+                state_->pathInfoCache.upsert(storePath.to_string(),
                     res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue{ .value = res.second });
                 if (res.first == NarInfoDiskCache::oInvalid ||
                     !goodStorePath(storePath, res.second->path))
@@ -701,7 +701,7 @@ void Store::queryPathInfo(const StorePath & storePath,
 
                 {
                     auto state_(state.lock());
-                    state_->pathInfoCache.upsert(std::string(storePath.to_string()), PathInfoCacheValue { .value = info });
+                    state_->pathInfoCache.upsert(storePath.to_string(), PathInfoCacheValue { .value = info });
                 }
 
                 if (!info || !goodStorePath(storePath, info->path)) {
diff --git a/src/libutil/include/nix/util/lru-cache.hh b/src/libutil/include/nix/util/lru-cache.hh
index 5fa3b34a6..20891a086 100644
--- a/src/libutil/include/nix/util/lru-cache.hh
+++ b/src/libutil/include/nix/util/lru-cache.hh
@@ -11,7 +11,7 @@ namespace nix {
 /**
  * A simple least-recently used cache. Not thread-safe.
  */
-template<typename Key, typename Value>
+template<typename Key, typename Value, typename Compare = std::less<>>
 class LRUCache
 {
 private:
@@ -22,7 +22,7 @@ private:
     // and LRU.
     struct LRUIterator;
 
-    using Data = std::map<Key, std::pair<LRUIterator, Value>>;
+    using Data = std::map<Key, std::pair<LRUIterator, Value>, Compare>;
     using LRU = std::list<typename Data::iterator>;
 
     struct LRUIterator
@@ -43,7 +43,8 @@ public:
     /**
      * Insert or upsert an item in the cache.
      */
-    void upsert(const Key & key, const Value & value)
+    template<typename K>
+    void upsert(const K & key, const Value & value)
     {
         if (capacity == 0)
             return;
@@ -68,7 +69,8 @@ public:
         i->second.first.it = j;
     }
 
-    bool erase(const Key & key)
+    template<typename K>
+    bool erase(const K & key)
     {
         auto i = data.find(key);
         if (i == data.end())
@@ -82,7 +84,8 @@ public:
      * Look up an item in the cache. If it exists, it becomes the most
      * recently used item.
      * */
-    std::optional<Value> get(const Key & key)
+    template<typename K>
+    std::optional<Value> get(const K & key)
     {
         auto i = data.find(key);
         if (i == data.end())