Add debug logging facility

include/cppast/diagnostic.hpp

@@ -66,6 +66,7 @@ namespace cppast
     /// The severity of a [cppast::diagnostic]().
     enum class severity
     {
+        debug,    //< A debug diagnostic that is just for debugging purposes.
         warning,  //< A warning that doesn't impact AST generation.
         error,    //< A non-critical error that does impact AST generation but not critically.
         critical, //< A critical error where AST generation isn't possible.
@@ -77,6 +78,8 @@ namespace cppast
     {
         switch (s)
         {
+        case severity::debug:
+            return "debug";
         case severity::warning:
             return "warning";
         case severity::error:

include/cppast/parser.hpp

@@ -43,10 +43,23 @@ namespace cppast
             return error_;
         }
 
+        /// \effects Sets whether or not the logger prints debugging diagnostics.
+        void set_verbose(bool value) noexcept
+        {
+            verbose_ = value;
+        }
+
+        /// \returns Whether or not the logger prints debugging diagnostics.
+        bool is_verbose() const noexcept
+        {
+            return verbose_;
+        }
+
     private:
         virtual bool do_log(const char* source, const diagnostic& d) const = 0;
 
         mutable std::atomic<bool> error_;
+        bool                      verbose_ = false;
     };
 
     /// A [cppast::diagnostic_logger]() that logs to `stderr`.