[clangd] Temporary fix for bad inference in Decision Forest.

[usaxena95]

Summary

Unreachable file distances are represented as
std::numeric_limits<unsigned>::max().
The dataset recorded the signals as signed int capturing this default
value as -1.
The dataset needs to regenerated and a new model is required that
interprets this unreachable as the intended value.

This temporarily fixes this by interpreting unreachable distance as -1
and would be removed once we have the correct model.

One can look of these occurrences by searching for -0.5 in
clang-tools-extra/clangd/quality/model/forest.json.

[adamcz]

LG, but I'm not sure if we really need it. Up to you.

[usaxena95]

Yeah. Not very critical as of now. You can patch it if you want incase you want to try it.

clang-tools-extra/clangd/Quality.cpp

float evaluateDecisionForest(const SymbolQualitySignals &Quality,
   E.setSymbolCategory(Quality.Category);
 
   SymbolRelevanceSignals::DerivedSignals Derived =
       Relevance.calculateDerivedSignals();
   E.setIsNameInContext(Derived.NameMatchesContext);
   E.setIsForbidden(Relevance.Forbidden);
   E.setIsInBaseClass(Relevance.InBaseClass);
   E.setFileProximityDistance(Derived.FileProximityDistance);
+  // FIXME(usx): Remove interpretation of Unreachable distance as -1 once we
+  // have a new model.
+  E.setFileProximityDistance(Derived.FileProximityDistance ==
+                                     FileDistance::Unreachable
+                                 ? -1
+                                 : Derived.FileProximityDistance);
   E.setSemaFileProximityScore(Relevance.SemaFileProximityScore);
-  E.setSymbolScopeDistance(Derived.ScopeProximityDistance);
+  E.setSymbolScopeDistance(Derived.ScopeProximityDistance ==
+                                   FileDistance::Unreachable
+                               ? -1
+                               : Derived.ScopeProximityDistance);
   E.setSemaSaysInScope(Relevance.SemaSaysInScope);
   E.setScope(Relevance.Scope);
   E.setContextKind(Relevance.Context);
   E.setIsInstanceMember(Relevance.IsInstanceMember);
   E.setHadContextType(Relevance.HadContextType);
   E.setHadSymbolType(Relevance.HadSymbolType);
   E.setTypeMatchesPreferred(Relevance.TypeMatchesPreferred);
   E.setFilterLength(Relevance.FilterLength);