LLDB-MI: -var-list-children with no children doesn't need a children value in the response.

[brucem]

Summary

When using GDB with MI, if there aren't children for a variable,
it doesn't include a "children" value in the response. LLDB does
and sets it to "[]" while variables with children have an unquoted
list: children=[...].

This removes the children value entirely when there are no children
making this match GDB in behavior.

[abidh]

Looks good.

test/tools/lldb-mi/variable/TestMiVar.py

def test_lldbmi_eval(self):
         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\"")
         self.runCmd("-var-show-attributes var2")
         self.expect("\^done,status=\"editable\"")
         self.runCmd("-var-list-children var2")
-        self.expect("\^done,numchild=\"0\",children=\"\[\]\"")
+        self.expect("\^done,numchild=\"0\"")
         self.runCmd("-data-evaluate-expression \"g_MyVar=30\"")
         self.expect("\^done,value=\"30\"")
         self.runCmd("-var-update --all-values var2")
         #self.expect("\^done,changelist=\[\{name=\"var2\",value=\"30\",in_scope=\"true\",type_changed=\"false\",has_more=\"0\"\}\]") #FIXME -var-update doesn't work
         self.runCmd("-var-delete var2")
         self.expect("\^done")
         self.runCmd("-var-create var2 * g_MyVar")
         self.expect("\^done,name=\"var2\",numchild=\"0\",value=\"30\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
 
         # Print static "s_MyVar", modify, delete and create again
         self.runCmd("-data-evaluate-expression s_MyVar")
         self.expect("\^done,value=\"30\"")
         self.runCmd("-var-create var3 * s_MyVar")
         self.expect("\^done,name=\"var3\",numchild=\"0\",value=\"30\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
         self.runCmd("-var-evaluate-expression var3")
         self.expect("\^done,value=\"30\"")
         self.runCmd("-var-show-attributes var3")
         self.expect("\^done,status=\"editable\"")
         self.runCmd("-var-list-children var3")
-        self.expect("\^done,numchild=\"0\",children=\"\[\]\"")
+        self.expect("\^done,numchild=\"0\"")
         self.runCmd("-data-evaluate-expression \"s_MyVar=3\"")
         self.expect("\^done,value=\"3\"")
         self.runCmd("-var-update --all-values var3")
         #self.expect("\^done,changelist=\[\{name=\"var3\",value=\"3\",in_scope=\"true\",type_changed=\"false\",has_more=\"0\"\}\]") #FIXME -var-update doesn't work
         self.runCmd("-var-delete var3")
         self.expect("\^done")
         self.runCmd("-var-create var3 * s_MyVar")
         self.expect("\^done,name=\"var3\",numchild=\"0\",value=\"3\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
 
         # Print local "b", modify, delete and create again
         self.runCmd("-data-evaluate-expression b")
         self.expect("\^done,value=\"20\"")
         self.runCmd("-var-create var4 * b")
         self.expect("\^done,name=\"var4\",numchild=\"0\",value=\"20\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
         self.runCmd("-var-evaluate-expression var4")
         self.expect("\^done,value=\"20\"")
         self.runCmd("-var-show-attributes var4")
         self.expect("\^done,status=\"editable\"")
         self.runCmd("-var-list-children var4")
-        self.expect("\^done,numchild=\"0\",children=\"\[\]\"")
+        self.expect("\^done,numchild=\"0\"")
         self.runCmd("-data-evaluate-expression \"b=2\"")
         self.expect("\^done,value=\"2\"")
         self.runCmd("-var-update --all-values var4")
         #self.expect("\^done,changelist=\[\{name=\"var4\",value=\"2\",in_scope=\"true\",type_changed=\"false\",has_more=\"0\"\}\]") #FIXME -var-update doesn't work
         self.runCmd("-var-delete var4")
         self.expect("\^done")
         self.runCmd("-var-create var4 * b")
         self.expect("\^done,name=\"var4\",numchild=\"0\",value=\"2\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
 
         # Print temp "a + b"
         self.runCmd("-data-evaluate-expression \"a + b\"")
         self.expect("\^done,value=\"12\"")
         self.runCmd("-var-create var5 * \"a + b\"")
         self.expect("\^done,name=\"var5\",numchild=\"0\",value=\"12\",type=\"int\",thread-id=\"1\",has_more=\"0\"")
         self.runCmd("-var-evaluate-expression var5")
         self.expect("\^done,value=\"12\"")
         self.runCmd("-var-show-attributes var5")
         self.expect("\^done,status=\"editable\"") #FIXME editable or not?
         self.runCmd("-var-list-children var5")
-        self.expect("\^done,numchild=\"0\",children=\"\[\]\"")
+        self.expect("\^done,numchild=\"0\"")
 
         # Print argument "argv[0]"
         self.runCmd("-data-evaluate-expression \"argv[0]\"")
         self.expect("\^done,value=\"0x[0-9a-f]+\"")
         self.runCmd("-var-create var6 * \"argv[0]\"")
         self.expect("\^done,name=\"var6\",numchild=\"1\",value=\"0x[0-9a-f]+ \\\\\\\".*?%s\\\\\\\"\",type=\"const char \*\",thread-id=\"1\",has_more=\"0\"" % self.myexe)
         self.runCmd("-var-evaluate-expression var6")
         self.expect("\^done,value=\"0x[0-9a-f]+ \\\\\\\".*?%s\\\\\\\"\"" % self.myexe)

tools/lldb-mi/MICmdCmdVar.cpp

CMICmdCmdVarListChildren::Acknowledge(void)
     if (m_bValueValid)
     {
         // MI print "%s^done,numchild=\"%u\",children=[]""
         const CMIUtilString strNumChild(CMIUtilString::Format("%u", m_nChildren));
         const CMICmnMIValueConst miValueConst(strNumChild);
         CMICmnMIValueResult miValueResult("numchild", miValueConst);
 
         VecMIValueResult_t::const_iterator it = m_vecMiValueResult.begin();
-        if (it == m_vecMiValueResult.end())
-        {
-            const CMICmnMIValueConst miValueConst("[]");
-            miValueResult.Add("children", miValueConst);
-        }
-        else
+        if (it != m_vecMiValueResult.end())
         {
             CMICmnMIValueList miValueList(*it);
             ++it;
             while (it != m_vecMiValueResult.end())
             {
                 const CMICmnMIValueResult &rResult(*it);
                 miValueList.Add(rResult);