[lldb][NFC] Move ShouldShow/ShouldSelect logic into Stopinfo (#134160)

This NFC patch simplifies the main loop in HandleProcessStateChanged
event by moving duplicated code into the StopInfo class, also allowing
StopInfo subclasses to override behavior.

More specifically, two functions are created:

* ShouldShow: should a Thread with such StopInfo should be printed when
the debugger stops? Currently, no StopInfo subclasses override this, but
a subsequent patch will fix a bug by making StopInfoBreakpoint check
whether the breakpoint is internal.

* ShouldSelect: should a Thread with such a StopInfo be selected? This
is currently overridden by StopInfoUnixSignal but will, in the future,
be overridden by StopInfoBreakpoint.

Author: felipepiovezan

lldb/include/lldb/Target/StopInfo.h

@@ -118,6 +118,19 @@ class StopInfo : public std::enable_shared_from_this<StopInfo> {
 
   StructuredData::ObjectSP GetExtendedInfo() { return m_extended_info; }
 
+  /// Returns true if this is a stop reason that should be shown to a user when
+  /// viewing the thread with this stop info.
+  virtual bool ShouldShow() const { return IsValid(); }
+
+  /// Returns true if this is a stop reason that should cause a thread to be
+  /// selected when stopping.
+  virtual bool ShouldSelect() const {
+    lldb::StopReason reason = GetStopReason();
+    return reason != lldb::eStopReasonNone &&
+           reason != lldb::eStopReasonHistoryBoundary &&
+           reason != lldb::eStopReasonInvalid;
+  }
+
   static lldb::StopInfoSP
   CreateStopReasonWithBreakpointSiteID(Thread &thread,
                                        lldb::break_id_t break_id);

lldb/source/Target/Process.cpp

@@ -808,85 +808,36 @@ bool Process::HandleProcessStateChangedEvent(
         std::lock_guard<std::recursive_mutex> guard(thread_list.GetMutex());
 
         ThreadSP curr_thread(thread_list.GetSelectedThread());
-        ThreadSP thread;
-        StopReason curr_thread_stop_reason = eStopReasonInvalid;
-        bool prefer_curr_thread = false;
-        if (curr_thread && curr_thread->IsValid()) {
-          curr_thread_stop_reason = curr_thread->GetStopReason();
-          switch (curr_thread_stop_reason) {
-          case eStopReasonNone:
-          case eStopReasonInvalid:
-            // Don't prefer the current thread if it didn't stop for a reason.
-            break;
-          case eStopReasonSignal: {
-            // We need to do the same computation we do for other threads
-            // below in case the current thread happens to be the one that
-            // stopped for the no-stop signal.
-            uint64_t signo = curr_thread->GetStopInfo()->GetValue();
-            if (process_sp->GetUnixSignals()->GetShouldStop(signo))
-              prefer_curr_thread = true;
-          } break;
-          default:
-            prefer_curr_thread = true;
-            break;
-          }
+
+        if (curr_thread && curr_thread->IsValid())
           curr_thread_stop_info_sp = curr_thread->GetStopInfo();
-        }
+        bool prefer_curr_thread = curr_thread_stop_info_sp &&
+                                  curr_thread_stop_info_sp->ShouldSelect();
 
         if (!prefer_curr_thread) {
           // Prefer a thread that has just completed its plan over another
           // thread as current thread.
           ThreadSP plan_thread;
           ThreadSP other_thread;
 
-          const size_t num_threads = thread_list.GetSize();
-          size_t i;
-          for (i = 0; i < num_threads; ++i) {
-            thread = thread_list.GetThreadAtIndex(i);
-            StopReason thread_stop_reason = thread->GetStopReason();
-            switch (thread_stop_reason) {
-            case eStopReasonInvalid:
-            case eStopReasonNone:
-            case eStopReasonHistoryBoundary:
-              break;
-
-            case eStopReasonSignal: {
-              // Don't select a signal thread if we weren't going to stop at
-              // that signal.  We have to have had another reason for stopping
-              // here, and the user doesn't want to see this thread.
-              uint64_t signo = thread->GetStopInfo()->GetValue();
-              if (process_sp->GetUnixSignals()->GetShouldStop(signo)) {
-                if (!other_thread)
-                  other_thread = thread;
-              }
-              break;
-            }
-            case eStopReasonTrace:
-            case eStopReasonBreakpoint:
-            case eStopReasonWatchpoint:
-            case eStopReasonException:
-            case eStopReasonExec:
-            case eStopReasonFork:
-            case eStopReasonVFork:
-            case eStopReasonVForkDone:
-            case eStopReasonThreadExiting:
-            case eStopReasonInstrumentation:
-            case eStopReasonProcessorTrace:
-            case eStopReasonInterrupt:
-              if (!other_thread)
-                other_thread = thread;
-              break;
-            case eStopReasonPlanComplete:
+          for (ThreadSP thread : thread_list.Threads()) {
+            StopInfoSP stop_info = thread->GetStopInfo();
+            if (!stop_info || !stop_info->ShouldSelect())
+              continue;
+            StopReason thread_stop_reason = stop_info->GetStopReason();
+            if (thread_stop_reason == eStopReasonPlanComplete) {
               if (!plan_thread)
                 plan_thread = thread;
-              break;
+            } else if (!other_thread) {
+              other_thread = thread;
             }
           }
           if (plan_thread)
             thread_list.SetSelectedThreadByID(plan_thread->GetID());
           else if (other_thread)
             thread_list.SetSelectedThreadByID(other_thread->GetID());
           else {
+            ThreadSP thread;
             if (curr_thread && curr_thread->IsValid())
               thread = curr_thread;
             else
@@ -5832,7 +5783,7 @@ size_t Process::GetThreadStatus(Stream &strm,
     if (thread_sp) {
       if (only_threads_with_stop_reason) {
         StopInfoSP stop_info_sp = thread_sp->GetStopInfo();
-        if (!stop_info_sp || !stop_info_sp->IsValid())
+        if (!stop_info_sp || !stop_info_sp->ShouldShow())
           continue;
       }
       thread_sp->GetStatus(strm, start_frame, num_frames,

lldb/source/Target/StopInfo.cpp

@@ -1080,12 +1080,7 @@ class StopInfoUnixSignal : public StopInfo {
     return false;
   }
 
-  bool ShouldStop(Event *event_ptr) override {
-    ThreadSP thread_sp(m_thread_wp.lock());
-    if (thread_sp)
-      return thread_sp->GetProcess()->GetUnixSignals()->GetShouldStop(m_value);
-    return false;
-  }
+  bool ShouldStop(Event *event_ptr) override { return IsShouldStopSignal(); }
 
   // If should stop returns false, check if we should notify of this event
   bool DoShouldNotify(Event *event_ptr) override {
@@ -1137,9 +1132,17 @@ class StopInfoUnixSignal : public StopInfo {
     return m_description.c_str();
   }
 
+  bool ShouldSelect() const override { return IsShouldStopSignal(); }
+
 private:
   // In siginfo_t terms, if m_value is si_signo, m_code is si_code.
   std::optional<int> m_code;
+
+  bool IsShouldStopSignal() const {
+    if (ThreadSP thread_sp = m_thread_wp.lock())
+      return thread_sp->GetProcess()->GetUnixSignals()->GetShouldStop(m_value);
+    return false;
+  }
 };
 
 // StopInfoInterrupt