[lldb] Fix dwim-print error message for missing expr

(cherry picked from commit 4d18d97)

Author: kastiglione

lldb/source/Commands/CommandObjectDWIMPrint.cpp

@@ -63,14 +63,16 @@ bool CommandObjectDWIMPrint::DoExecute(StringRef command,
   OptionsWithRaw args{command};
   StringRef expr = args.GetRawPart();
 
+  if (expr.empty()) {
+    result.AppendErrorWithFormatv("'{0}' takes a variable or expression",
+                                  m_cmd_name);
+    return false;
+  }
+
   if (args.HasArgs()) {
     if (!ParseOptionsAndNotify(args.GetArgs(), result, m_option_group,
                                m_exe_ctx))
       return false;
-  } else if (command.empty()) {
-    result.AppendErrorWithFormatv("'{0}' takes a variable or expression",
-                                  m_cmd_name);
-    return false;
   }
 
   auto verbosity = GetDebugger().GetDWIMPrintVerbosity();

lldb/test/API/commands/dwim-print/TestDWIMPrint.py

@@ -113,6 +113,13 @@ def test_expression_language(self):
         self._expect_cmd(f"dwim-print -l c++ -- argc", "frame variable")
         self._expect_cmd(f"dwim-print -l c++ -- argc + 1", "expression")
 
+    def test_empty_expression(self):
+        self.build()
+        lldbutil.run_to_name_breakpoint(self, "main")
+        error_msg = "error: 'dwim-print' takes a variable or expression"
+        self.expect(f"dwim-print", error=True, startstr=error_msg)
+        self.expect(f"dwim-print -- ", error=True, startstr=error_msg)
+
     def test_nested_values(self):
         """Test dwim-print with nested values (structs, etc)."""
         self.build()