Refactor OnExit utility class in ClangUserExpression

[teemperor]

Summary

OnExit ensures we call ResetDeclMap before this method ends. However,
we also have a few manual calls to ResetDeclMap in there that are actually unnecessary
because of this (calling the method multiple times has no effect). This patch also moves
the class out of the method that we can reuse it for the upcoming method that handles
parsing for completion.

[labath]

How is this class different from lldb_private::CleanUp? Shouldn't we just delete it and replace all uses with the pre-existing class?

lldb/trunk/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

#define OBJC_CAST_HACK_TO "(int)(long long)["
   while ((from_offset = expr.find(OBJC_CAST_HACK_FROM)) != expr.npos)
     expr.replace(from_offset, sizeof(OBJC_CAST_HACK_FROM) - 1,
                  OBJC_CAST_HACK_TO);
 
 #undef OBJC_CAST_HACK_TO
 #undef OBJC_CAST_HACK_FROM
 }
 
+namespace {
+// Utility guard that calls a callback when going out of scope.
+class OnExit {
+public:
+  typedef std::function<void(void)> Callback;
+
+  OnExit(Callback const &callback) : m_callback(callback) {}
+
+  ~OnExit() { m_callback(); }
+
+private:
+  Callback m_callback;
+};
+} // namespace
+
 bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
                                 ExecutionContext &exe_ctx,
                                 lldb_private::ExecutionPolicy execution_policy,
                                 bool keep_result_in_memory,
                                 bool generate_debug_info) {
   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
 
   Status err;
bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
   //////////////////////////
   // Parse the expression
   //
 
   m_materializer_ap.reset(new Materializer());
 
   ResetDeclMap(exe_ctx, m_result_delegate, keep_result_in_memory);
 
-  class OnExit {
-  public:
-    typedef std::function<void(void)> Callback;
-
-    OnExit(Callback const &callback) : m_callback(callback) {}
-
-    ~OnExit() { m_callback(); }
-
-  private:
-    Callback m_callback;
-  };
-
   OnExit on_exit([this]() { ResetDeclMap(); });
 
   if (!DeclMap()->WillParse(exe_ctx, m_materializer_ap.get())) {
     diagnostic_manager.PutString(
         eDiagnosticSeverityError,
         "current process state is unsuitable for expression parsing");
-
-    ResetDeclMap(); // We are being careful here in the case of breakpoint
-                    // conditions.
-
     return false;
   }
 
   if (m_options.GetExecutionPolicy() == eExecutionPolicyTopLevel) {
     DeclMap()->SetLookupsEnabled(true);
   }
 
   Process *process = exe_ctx.GetProcessPtr();
if (diagnostic_manager.HasFixIts()) {
         const std::string &fixed_expression =
             diagnostic_manager.GetFixedExpression();
         if (ExpressionSourceCode::GetOriginalBodyBounds(
                 fixed_expression, lang_type, fixed_start, fixed_end))
           m_fixed_text =
               fixed_expression.substr(fixed_start, fixed_end - fixed_start);
       }
     }
-
-    ResetDeclMap(); // We are being careful here in the case of breakpoint
-                    // conditions.
-
     return false;
   }
 
   //////////////////////////////////////////////////////////////////////////////////////////
   // Prepare the output of the parser for execution, evaluating it statically
   // if possible
   //
 
if (jit_module_sp) {
       FileSpec jit_file;
       jit_file.GetFilename() = const_func_name;
       jit_module_sp->SetFileSpecAndObjectName(jit_file, ConstString());
       m_jit_module_wp = jit_module_sp;
       target->GetImages().Append(jit_module_sp);
     }
   }
 
-  ResetDeclMap(); // Make this go away since we don't need any of its state
-                  // after parsing.  This also gets rid of any
-                  // ClangASTImporter::Minions.
-
   if (process && m_jit_start_addr != LLDB_INVALID_ADDRESS)
     m_jit_process_wp = lldb::ProcessWP(process->shared_from_this());
   return true;
 }
 
 bool ClangUserExpression::AddArguments(ExecutionContext &exe_ctx,
                                        std::vector<lldb::addr_t> &args,
                                        lldb::addr_t struct_address,