Make "process attach -c" work again, add a test for it.

[jingham]

Summary

process attach -c

stopped working at some point. Since there was no test for this feature, I'm not sure when it broke, but I think it was when we started being more rigorous about tracking the interpreter execution context.

The continue in the CommandObjectProcessAttach was handled by calling HandleCommand("process attach", ...). That seems a little odd at first blush, but makes sense because it means the result of the continue gets reported just as an ordinary user "continue" would.

The problem is that though we've made a new process (and maybe even a new target) in the basic attach command, we haven't told the command interpreter about them yet, so CheckRequirements will fail before we get a chance to run the command.

In this case, since we know exactly which process we want to continue, we should just be explicit and pass an execution context for that process to HandleCommand.

Also added a test for this.

[JDevlieghere]

LGTM. Thanks Jim!

lldb/source/Commands/CommandObjectProcess.cpp

bool DoExecute(Args &command, CommandReturnObject &result) override {
 
     if (command.GetArgumentCount()) {
       result.AppendErrorWithFormat("Invalid arguments for '%s'.\nUsage: %s\n",
                                    m_cmd_name.c_str(), m_cmd_syntax.c_str());
       return false;
     }
 
     StreamString stream;
+    ProcessSP process_sp;
     const auto error = target->Attach(m_options.attach_info, &stream);
     if (error.Success()) {
-      ProcessSP process_sp(target->GetProcessSP());
+      process_sp = target->GetProcessSP();
       if (process_sp) {
         result.AppendMessage(stream.GetString());
         result.SetStatus(eReturnStatusSuccessFinishNoResult);
         result.SetDidChangeProcessState(true);
       } else {
         result.AppendError(
             "no error returned from Target::Attach, and target has no process");
       }
if (!old_arch_spec.IsValid()) {
       result.AppendWarningWithFormat(
           "Architecture changed from %s to %s.\n",
           old_arch_spec.GetTriple().getTriple().c_str(),
           target->GetArchitecture().GetTriple().getTriple().c_str());
     }
 
     // This supports the use-case scenario of immediately continuing the
     // process once attached.
-    if (m_options.attach_info.GetContinueOnceAttached())
-      m_interpreter.HandleCommand("process continue", eLazyBoolNo, result);
+    if (m_options.attach_info.GetContinueOnceAttached()) {
+      // We have made a process but haven't told the interpreter about it yet,
+      // so CheckRequirements will fail for "process continue".  Set the override
+      // here:
+      ExecutionContext exe_ctx(process_sp);
+      m_interpreter.HandleCommand("process continue", eLazyBoolNo, exe_ctx, result);
+    }
 
     return result.Succeeded();
   }
 
   CommandOptions m_options;
 };
 
 // CommandObjectProcessContinue

lldb/test/API/commands/process/attach/TestProcessAttach.py

def test_attach_to_process_by_id(self):
 
         self.runCmd("process attach -p " + str(popen.pid))
 
         target = self.dbg.GetSelectedTarget()
 
         process = target.GetProcess()
         self.assertTrue(process, PROCESS_IS_VALID)
 
+    @skipIfiOSSimulator
+    def test_attach_to_process_by_id_autocontinue(self):
+        """Test attach by process id"""
+        self.build()
+        exe = self.getBuildArtifact(exe_name)
+
+        # Spawn a new process
+        popen = self.spawnSubprocess(exe)
+
+        self.runCmd("process attach -c -p " + str(popen.pid))
+
+        target = self.dbg.GetSelectedTarget()
+
+        process = target.GetProcess()
+        self.assertTrue(process, PROCESS_IS_VALID)
+        self.assertTrue(process.GetState(), lldb.eStateRunning)
+
     @skipIfReproducer # FIXME: Unexpected packet during (active) replay
     @skipIfWindows # This is flakey on Windows AND when it fails, it hangs: llvm.org/pr48806
     def test_attach_to_process_from_different_dir_by_id(self):
         """Test attach by process id"""
         newdir = self.getBuildArtifact("newdir")
         try:
             os.mkdir(newdir)
         except OSError as e: