[PATCH] MI: PR20684, preserve user selected thread and frame when invoking MI commands

[Jan Vrany <jan.vrany@labware.com>]

When invoking MI commands with --thread and/or --frame, user selected
thread and frame was not preserved:

  (gdb)
  info thread
  &"info thread\n"
  ~"  Id   Target Id                                           Frame \n"
  ~"* 1    Thread 0x7ffff7c30740 (LWP 19302) \"user-selected-c\" main () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60\n"
  ~"  2    Thread 0x7ffff7c2f700 (LWP 19306) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ~"  3    Thread 0x7ffff742e700 (LWP 19307) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ^done
  (gdb)
  info frame
  &"info frame\n"
  ~"Stack level 0, frame at 0x7fffffffdf90:\n"
  ~" rip = 0x555555555207 in main (/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60); saved rip = 0x7ffff7c5709b\n"
  ~" source language c.\n"
  ~" Arglist at 0x7fffffffdf80, args: \n"
  ~" Locals at 0x7fffffffdf80, Previous frame's sp is 0x7fffffffdf90\n"
  ~" Saved registers:\n "
  ~" rbp at 0x7fffffffdf80, rip at 0x7fffffffdf88\n"
  ^done
  (gdb)
  -stack-info-depth --thread 3
  ^done,depth="4"
  (gdb)
  info thread
  &"info thread\n"
  ~"  Id   Target Id                                           Frame \n"
  ~"  1    Thread 0x7ffff7c30740 (LWP 19302) \"user-selected-c\" main () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:60\n"
  ~"  2    Thread 0x7ffff7c2f700 (LWP 19306) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ~"* 3    Thread 0x7ffff742e700 (LWP 19307) \"user-selected-c\" child_sub_function () at /home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30\n"
  ^done
  (gdb)
  info frame
  &"info frame\n"
  ~"Stack level 0, frame at 0x7ffff742dee0:\n"
  ~" rip = 0x555555555169 in child_sub_function (/home/uuu/gdb/gdb/testsuite/gdb.mi/user-selected-context-sync.c:30); saved rip = 0x555555555188\n"
  ~" called by frame at 0x7ffff742df00\n"
  ~" source language c.\n"
  ~" Arglist at 0x7ffff742ded0, args: \n"
  ~" Locals at 0x7ffff742ded0, Previous frame's sp is 0x7ffff742dee0\n"
  ~" Saved registers:\n "
  ~" rbp at 0x7ffff742ded0, rip at 0x7ffff742ded8\n"
  ^done
  (gdb)

This was problematic for frontends that provide access to CLI because UI
may silently change the context for CLI commands (as demonstrated above).

gdb/Changelog

	PR 20684
	* gdb/mi/mi-main.c (mi_cmd_execute): Preserve user selected thread
	and frame when invoking MI commands.
---
 gdb/ChangeLog    |  6 ++++++
 gdb/mi/mi-main.c | 36 +++++++++++++++---------------------
 2 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e67668d315c..ea232ff1b3f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2021-02-09  Jan Vrany  <jan.vrany@labware.com>
+
+	PR 20684
+	* gdb/mi/mi-main.c (mi_cmd_execute): Preserve user selected thread
+	and frame when invoking MI commands.
+
 2021-02-08  Shahab Vahedi  <shahab@synopsys.com>
 
 	PR tdep/27369
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 9a14d78e1e2..c5103800314 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -1971,25 +1971,13 @@ mi_execute_command (const char *cmd, int from_tty)
 	     again.  */
 	  && !command_notifies_uscc_observer (command.get ()))
 	{
-	  int report_change = 0;
-
-	  if (command->thread == -1)
-	    {
-	      report_change = (previous_ptid != null_ptid
-			       && inferior_ptid != previous_ptid
-			       && inferior_ptid != null_ptid);
-	    }
-	  else if (inferior_ptid != null_ptid)
-	    {
-	      struct thread_info *ti = inferior_thread ();
-
-	      report_change = (ti->global_num != command->thread);
-	    }
-
-	  if (report_change)
-	    {
-	      gdb::observers::user_selected_context_changed.notify
-		(USER_SELECTED_THREAD | USER_SELECTED_FRAME);
+	  if (command->thread == -1
+	      && previous_ptid != null_ptid
+	      && inferior_ptid != previous_ptid
+	      && inferior_ptid != null_ptid)
+            {
+              gdb::observers::user_selected_context_changed.notify
+                      (USER_SELECTED_THREAD | USER_SELECTED_FRAME);
 	    }
 	}
     }
@@ -2035,6 +2023,7 @@ mi_cmd_execute (struct mi_parse *parse)
       set_current_program_space (inf->pspace);
     }
 
+  gdb::optional<scoped_restore_current_thread> thread_saver;
   if (parse->thread != -1)
     {
       thread_info *tp = find_thread_global_id (parse->thread);
@@ -2045,9 +2034,11 @@ mi_cmd_execute (struct mi_parse *parse)
       if (tp->state == THREAD_EXITED)
 	error (_("Thread id: %d has terminated"), parse->thread);
 
+      thread_saver.emplace ();
       switch_to_thread (tp);
     }
 
+  gdb::optional<scoped_restore_selected_frame> frame_saver;
   if (parse->frame != -1)
     {
       struct frame_info *fid;
@@ -2055,8 +2046,11 @@ mi_cmd_execute (struct mi_parse *parse)
 
       fid = find_relative_frame (get_current_frame (), &frame);
       if (frame == 0)
-	/* find_relative_frame was successful */
-	select_frame (fid);
+        {
+          /* find_relative_frame was successful */
+          frame_saver.emplace ();
+          select_frame (fid);
+        }
       else
 	error (_("Invalid frame id: %d"), frame);
     }
-- 
2.30.0