[clangd] NFC: Change quality type to float

[kbobyrev]

Summary

For the sake of consistency, quality() should return float instead of double since all of the scoring calculation happens to be in floats. This should address a concern raised in D51481.

[sammccall]

If it's not too expensive, we can use the symbol quality metrics (from Quality.h) to do a more accurate prescore. Worth a benchmark :-)

[kbobyrev]

In D51636#1223204, @sammccall wrote:

If it's not too expensive, we can use the symbol quality metrics (from Quality.h) to do a more accurate prescore. Worth a benchmark :-)

Yes, I agree. We can investigate that quality/performance trade-off when we have more tools to simplify the process :)

clang-tools-extra/clangd/index/Index.h

struct Symbol {
   // FIXME: add extra fields for index scoring signals.
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Symbol &S);
 
 // Computes query-independent quality score for a Symbol.
 // This currently falls in the range [1, ln(#indexed documents)].
 // FIXME: this should probably be split into symbol -> signals
 //        and signals -> score, so it can be reused for Sema completions.
-double quality(const Symbol &S);
+float quality(const Symbol &S);
 
 // An immutable symbol container that stores a set of symbols.
 // The container will maintain the lifetime of the symbols.
 class SymbolSlab {
 public:
   using const_iterator = std::vector<Symbol>::const_iterator;
   using iterator = const_iterator;
 

clang-tools-extra/clangd/index/Index.cpp

if (static_cast<uint8_t>(O) & 1u << I)
       OS << Sigils[I];
   return OS;
 }
 
 raw_ostream &operator<<(raw_ostream &OS, const Symbol &S) {
   return OS << S.Scope << S.Name;
 }
 
-double quality(const Symbol &S) {
+float quality(const Symbol &S) {
   // This avoids a sharp gradient for tail symbols, and also neatly avoids the
   // question of whether 0 references means a bad symbol or missing data.
   if (S.References < 3)
     return 1;
   return std::log(S.References);
 }
 
 SymbolSlab::const_iterator SymbolSlab::find(const SymbolID &ID) const {