[clangd] Make SymbolLocation => bool conversion explicitly.

[hokein]

Summary

The implicit bool conversion could happen superisingly, e.g. when
checking if (Loc1 == Loc2), the compiler will convert SymbolLocation to
bool before comparing (because we don't define operator == for SymbolLocation).

[ilya-biryukov]

Scary....
Definitely LGTM!

clangd/index/Index.h

45–49

Maybe we should go even further and replace this with an isValid method? Conversion ops are confusing.

[sammccall]

Or make operator bool explicit

[hokein]

clangd/index/Index.h

45–49

I think making the bool operator explicit is sufficient to avoid the scary implicit-conversion problem.

clangd/index/Index.h

 
 struct SymbolLocation {
   // Specify a position (Line, Column) of symbol. Using Line/Column allows us to
   // build LSP responses without reading the file content.
   struct Position {
     uint32_t Line = 0; // 0-based
     // Using UTF-16 code units.
     uint32_t Column = 0; // 0-based
+    bool operator==(const Position& P) const {
+      return Line == P.Line && Column == P.Column;
+    }
   };
 
   // The URI of the source file where a symbol occurs.
   llvm::StringRef FileURI;
 
   /// The symbol range, using half-open range [Start, End).
   Position Start;
   Position End;
 
-  operator bool() const { return !FileURI.empty(); }
+  explicit operator bool() const { return !FileURI.empty(); }
+  bool operator==(const SymbolLocation& Loc) const {
+    return std::tie(FileURI, Start, End) ==
+           std::tie(Loc.FileURI, Loc.Start, Loc.End);
+  }
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const SymbolLocation &);
 
 // The class identifies a particular C++ symbol (class, function, method, etc).
 //
 // As USRs (Unified Symbol Resolution) could be large, especially for functions
 // with long type arguments, SymbolID is using 160-bits SHA1(USR) values to
 // guarantee the uniqueness of symbols while using a relatively small amount of