[clangd] Use ASTSignals in Heuristics CC Ranking.

[adamcz]

clang-tools-extra/clangd/Quality.cpp

477

Can you add a comment explaining how you chose those magic numbers? So that in the future, when someone needs to change it somehow, they have an idea of where this came from.

[usaxena95]

Added a comment about the calculation.

clang-tools-extra/clangd/Quality.cpp

float SymbolRelevanceSignals::evaluateHeuristics() const {
 
   if (InBaseClass)
     Score *= 0.5f;
 
   // Penalize for FixIts.
   if (NeedsFixIts)
     Score *= 0.5f;
 
+  // Use a sigmoid style boosting function similar to `References`, which flats
+  // out nicely for large values. This avoids a sharp gradient for heavily
+  // referenced symbols. Use smaller gradient for ScopeRefsInFile since ideally
+  // MainFileRefs <= ScopeRefsInFile.
+  if (MainFileRefs >= 2) {
+    // E.g.: (2, 1.12), (9, 2.0), (48, 3.0).
+    float S = std::pow(MainFileRefs, -0.11);
+    Score *= 11.0 * (1 - S) / (1 + S) + 0.7;
+  }
+  if (ScopeRefsInFile >= 2) {
+    // E.g.: (2, 1.04), (14, 2.0), (109, 3.0), (400, 3.6).
+    float S = std::pow(ScopeRefsInFile, -0.10);
+    Score *= 10.0 * (1 - S) / (1 + S) + 0.7;
+  }
+
   return Score;
 }
 
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS,
                               const SymbolRelevanceSignals &S) {
   OS << llvm::formatv("=== Symbol relevance: {0}\n", S.evaluateHeuristics());
   OS << llvm::formatv("\tName: {0}\n", S.Name);
   OS << llvm::formatv("\tName match: {0}\n", S.NameMatch);