Try to keep semantic highlighting colors stable across open files.

src/lru_cache.h

@@ -24,6 +24,11 @@ struct LruCache {
   // Inserts an entry. Evicts the oldest unused entry if there is no space.
   void Insert(const TKey& key, const std::shared_ptr<TValue>& value);
 
+  // Call |func| on existing entries. If |func| returns false iteration
+  // temrinates early.
+  template <typename TFunc>
+  void IterateValues(TFunc func);
+
  private:
   // There is a global score counter, when we access an element we increase
   // its score to the current global value, so it has the highest overall
@@ -113,6 +118,15 @@ void LruCache<TKey, TValue>::Insert(const TKey& key,
   entries_.push_back(entry);
 }
 
+template <typename TKey, typename TValue>
+template <typename TFunc>
+void LruCache<TKey, TValue>::IterateValues(TFunc func) {
+  for (Entry& entry : entries_) {
+    if (!func(entry.value))
+      break;
+  }
+}
+
 template <typename TKey, typename TValue>
 void LruCache<TKey, TValue>::IncrementScore() {
   next_score_ += 1;

src/semantic_highlight_symbol_cache.cc

@@ -1,31 +1,60 @@
 #include "semantic_highlight_symbol_cache.h"
 
-SemanticHighlightSymbolCache::Entry::Entry(const std::string& path)
-    : path(path) {}
+SemanticHighlightSymbolCache::Entry::Entry(
+    SemanticHighlightSymbolCache* all_caches,
+    const std::string& path)
+    : all_caches_(all_caches), path(path) {}
+
+optional<int> SemanticHighlightSymbolCache::Entry::TryGetStableId(
+    SymbolKind kind,
+    const std::string& detailed_name) {
+  TNameToId* map = GetMapForSymbol_(kind);
+  auto it = map->find(detailed_name);
+  if (it != map->end())
+    return it->second;
+
+  return nullopt;
+}
 
 int SemanticHighlightSymbolCache::Entry::GetStableId(
     SymbolKind kind,
     const std::string& detailed_name) {
-  TNameToId* map = nullptr;
+  optional<int> id = TryGetStableId(kind, detailed_name);
+  if (id)
+    return *id;
+
+  // Create a new id. First try to find a key in another map.
+  all_caches_->cache_.IterateValues([&](const std::shared_ptr<Entry>& entry) {
+    optional<int> other_id = entry->TryGetStableId(kind, detailed_name);
+    if (other_id) {
+      id = other_id;
+      return false;
+    }
+    return true;
+  });
+
+  // Create a new id.
+  TNameToId* map = GetMapForSymbol_(kind);
+  if (!id)
+    id = all_caches_->next_stable_id_++;
+  return (*map)[detailed_name] = *id;
+}
+
+SemanticHighlightSymbolCache::Entry::TNameToId*
+SemanticHighlightSymbolCache::Entry::GetMapForSymbol_(SymbolKind kind) {
   switch (kind) {
     case SymbolKind::Type:
-      map = &detailed_type_name_to_stable_id;
-      break;
+      return &detailed_type_name_to_stable_id;
     case SymbolKind::Func:
-      map = &detailed_func_name_to_stable_id;
-      break;
+      return &detailed_func_name_to_stable_id;
     case SymbolKind::Var:
-      map = &detailed_var_name_to_stable_id;
+      return &detailed_var_name_to_stable_id;
+    case SymbolKind::File:
+    case SymbolKind::Invalid:
       break;
-    default:
-      assert(false);
-      return 0;
   }
-  assert(map);
-  auto it = map->find(detailed_name);
-  if (it != map->end())
-    return it->second;
-  return (*map)[detailed_name] = map->size();
+  assert(false);
+  return nullptr;
 }
 
 SemanticHighlightSymbolCache::SemanticHighlightSymbolCache()
@@ -33,5 +62,6 @@ SemanticHighlightSymbolCache::SemanticHighlightSymbolCache()
 
 std::shared_ptr<SemanticHighlightSymbolCache::Entry>
 SemanticHighlightSymbolCache::GetCacheForFile(const std::string& path) {
-  return cache_.Get(path, [&]() { return std::make_shared<Entry>(path); });
+  return cache_.Get(
+      path, [&, this]() { return std::make_shared<Entry>(this, path); });
 }

src/semantic_highlight_symbol_cache.h

@@ -6,10 +6,15 @@
 #include <string>
 #include <unordered_map>
 
+using std::experimental::nullopt;
+using std::experimental::optional;
+
 // Caches symbols for a single file for semantic highlighting to provide
 // relatively stable ids. Only supports xxx files at a time.
 struct SemanticHighlightSymbolCache {
   struct Entry {
+    SemanticHighlightSymbolCache* all_caches_ = nullptr;
+
     // The path this cache belongs to.
     std::string path;
     // Detailed symbol name to stable id.
@@ -18,13 +23,18 @@ struct SemanticHighlightSymbolCache {
     TNameToId detailed_func_name_to_stable_id;
     TNameToId detailed_var_name_to_stable_id;
 
-    explicit Entry(const std::string& path);
+    Entry(SemanticHighlightSymbolCache* all_caches, const std::string& path);
 
+    optional<int> TryGetStableId(SymbolKind kind,
+                                 const std::string& detailed_name);
     int GetStableId(SymbolKind kind, const std::string& detailed_name);
+
+    TNameToId* GetMapForSymbol_(SymbolKind kind);
   };
 
   constexpr static int kCacheSize = 10;
   LruCache<std::string, Entry> cache_;
+  uint32_t next_stable_id_ = 0;
 
   SemanticHighlightSymbolCache();