1 files changed, 36 insertions, 10 deletions

diff --git a/lldb/source/Commands/CommandObjectMultiword.cpp b/lldb/source/Commands/CommandObjectMultiword.cpp
index 4efa565..ab3369c 100644
--- a/lldb/source/Commands/CommandObjectMultiword.cpp
+++ b/lldb/source/Commands/CommandObjectMultiword.cpp
@@ -194,28 +194,54 @@ void CommandObjectMultiword::Execute(const char *args_string,
 
   std::string error_msg;
   const size_t num_subcmd_matches = matches.GetSize();
-  if (num_subcmd_matches > 0)
+  if (num_subcmd_matches > 0) {
     error_msg.assign("ambiguous command ");
-  else
-    error_msg.assign("invalid command ");
-
-  error_msg.append("'");
-  error_msg.append(std::string(GetCommandName()));
-  error_msg.append(" ");
-  error_msg.append(std::string(sub_command));
-  error_msg.append("'.");
+    error_msg.append("'");
+    error_msg.append(std::string(GetCommandName()));
+    error_msg.append(" ");
+    error_msg.append(std::string(sub_command));
+    error_msg.append("'.");
 
-  if (num_subcmd_matches > 0) {
     error_msg.append(" Possible completions:");
     for (const std::string &match : matches) {
       error_msg.append("\n\t");
       error_msg.append(match);
     }
+  } else {
+    // Try to offer some alternatives to help correct the command.
+    error_msg.assign(
+        llvm::Twine("\"" + sub_command + "\" is not a valid subcommand of \"" +
+                    GetCommandName() + "\"." + GetSubcommandsHintText() +
+                    " Use \"help " + GetCommandName() + "\" to find out more.")
+            .str());
   }
   error_msg.append("\n");
   result.AppendRawError(error_msg.c_str());
 }
 
+std::string CommandObjectMultiword::GetSubcommandsHintText() {
+  if (m_subcommand_dict.empty())
+    return "";
+  const size_t maxCount = 5;
+  size_t i = 0;
+  std::string buffer = " Valid subcommand";
+  buffer.append(m_subcommand_dict.size() > 1 ? "s are:" : " is");
+  CommandMap::iterator pos;
+  for (pos = m_subcommand_dict.begin();
+       pos != m_subcommand_dict.end() && i < maxCount; ++pos, ++i) {
+    buffer.append(" ");
+    buffer.append(pos->first);
+    buffer.append(",");
+  }
+  if (i < m_subcommand_dict.size())
+    buffer.append(" and others");
+  else
+    buffer.pop_back();
+
+  buffer.append(".");
+  return buffer;
+}
+
 void CommandObjectMultiword::GenerateHelpText(Stream &output_stream) {
   // First time through here, generate the help text for the object and push it
   // to the return result object as well