[lldb-mi] print real error message in "-data-evaluate-expression"

[evgeny777]

Summary

Unlike "-var-create", the "-data-evaluate-expression" command always prints "Could not evaluate expression" when error occurs.

packages/Python/lldbsuite/test/tools/lldb-mi/variable/TestMiVar.py

def test_lldbmi_eval(self):
         self.runCmd("-exec-run")
         self.expect("\^running")
         self.expect("\*stopped,reason=\"breakpoint-hit\"")
 
         # Print non-existant variable
         self.runCmd("-var-create var1 * undef")
         self.expect("\^error,msg=\"error: error: use of undeclared identifier \'undef\'\\\\nerror: 1 errors parsing expression\\\\n\"")
         self.runCmd("-data-evaluate-expression undef")
-        self.expect("\^error,msg=\"Could not evaluate expression\"")
+        self.expect("\^error,msg=\"error: use of undeclared identifier \'undef\'\\\\nerror: 1 errors parsing expression\\\\n\"")
 
         # Print global "g_MyVar", modify, delete and create again
         self.runCmd("-data-evaluate-expression g_MyVar")
         self.expect("\^done,value=\"3\"")
         self.runCmd("-var-create var2 * g_MyVar")
         self.expect("\^done,name=\"var2\",numchild=\"0\",value=\"3\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
         self.runCmd("-var-evaluate-expression var2")
         self.expect("\^done,value=\"3\"")

tools/lldb-mi/MICmdCmdData.h

 //              For an introduction to adding a new command see CMICmdCmdSupportInfoMiCmdQuery
 //              command class as an example.
 //
 
 #pragma once
 
 // Third party headers:
 #include "lldb/API/SBCommandReturnObject.h"
+#include "lldb/API/SBError.h"
 
 // In-house headers:
 #include "MICmdBase.h"
 #include "MICmnMIValueTuple.h"
 #include "MICmnMIValueList.h"
 #include "MICmnLLDBDebugSessionInfoVarObj.h"
 
 //++ ============================================================================
public:
     // Methods:
   private:
     bool HaveInvalidCharacterInExpression(const CMIUtilString &vrExpr, char &vrwInvalidChar);
 
     // Attributes:
   private:
     bool m_bExpressionValid;     // True = yes is valid, false = not valid
     bool m_bEvaluatedExpression; // True = yes is expression evaluated, false = failed
+    lldb::SBError m_Error;       // Error object, which is examined when m_bEvaluatedExpression is false 
     CMIUtilString m_strValue;
     CMICmnMIValueTuple m_miValueTuple;
     bool m_bFoundInvalidChar; // True = yes found unexpected character in the expression, false = all ok
     char m_cExpressionInvalidChar;
     const CMIUtilString m_constStrArgExpr;
 };
 
 //++ ============================================================================

tools/lldb-mi/MICmdCmdData.cpp

CMICmdCmdDataEvaluateExpression::Execute()
     lldb::SBProcess sbProcess = rSessionInfo.GetProcess();
     lldb::SBThread thread = sbProcess.GetSelectedThread();
     m_bExpressionValid = (thread.GetNumFrames() > 0);
     if (!m_bExpressionValid)
         return MIstatus::success;
 
     lldb::SBFrame frame = thread.GetSelectedFrame();
     lldb::SBValue value = frame.EvaluateExpression(rExpression.c_str());
-    if (!value.IsValid() || value.GetError().Fail())
+    m_Error = value.GetError();
+    if (!value.IsValid() || m_Error.Fail())
         value = frame.FindVariable(rExpression.c_str());
     const CMICmnLLDBUtilSBValue utilValue(value, true);
     if (!utilValue.IsValid() || utilValue.IsValueUnknown())
     {
         m_bEvaluatedExpression = false;
         return MIstatus::success;
     }
     if (!utilValue.HasName())
if (m_bExpressionValid)
             }
 
             const CMICmnMIValueConst miValueConst(m_strValue);
             const CMICmnMIValueResult miValueResult("value", miValueConst);
             const CMICmnMIResultRecord miRecordResult(m_cmdData.strMiCmdToken, CMICmnMIResultRecord::eResultClass_Done, miValueResult);
             m_miResultRecord = miRecordResult;
             return MIstatus::success;
         }
-
-        const CMICmnMIValueConst miValueConst("Could not evaluate expression");
+        CMIUtilString mi_error_msg = "Could not evaluate expression";
+        if (const char* err_msg = m_Error.GetCString())
+            mi_error_msg = err_msg;
+        const CMICmnMIValueConst miValueConst(mi_error_msg.Escape(true));
         const CMICmnMIValueResult miValueResult("msg", miValueConst);
         const CMICmnMIResultRecord miRecordResult(m_cmdData.strMiCmdToken, CMICmnMIResultRecord::eResultClass_Error, miValueResult);
         m_miResultRecord = miRecordResult;
         return MIstatus::success;
     }
 
     const CMICmnMIValueConst miValueConst("Invalid expression");
     const CMICmnMIValueResult miValueResult("msg", miValueConst);