[PATCH] Make "list" work again in TUI

[Tom Tromey]

PR tui/18932 noted that commmit 0986c7 ("Replace TUI's select_frame
hook") regressed the ability to use the "list" command.  Previously
one could use "list" to temporarily change what was displayed in the
source window, but after that patch, the "list" command seems to have
no effect -- "seems to", because what actually happens is that the
list command does change the content, but
tui_refresh_frame_and_register_information immediately changes it
back.

This patch makes the "list" command work again by adding some caching.
Now the TUI tracks the previously displayed frame, PC, and inferior;
and only updates the display if one of these was changed by the
previous command.

gdb/ChangeLog
2018-09-08  Tom Tromey  <tom@tromey.com>

	PR tui/18932:
	* tui/tui-hooks.c (last_frame_id, last_frame_pc, last_inferior):
	New globals.
	(clear_inferior_cache): New function.
	(tui_refresh_frame_and_register_information): Cache frame, PC, and
	inferior to decide when to update.
	(_initialize_tui_hooks): Attach clear_inferior_cache to observer.
---
 gdb/ChangeLog       | 10 +++++++
 gdb/tui/tui-hooks.c | 80 +++++++++++++++++++++++++++++++++++++++--------------
 2 files changed, 70 insertions(+), 20 deletions(-)

diff --git a/gdb/tui/tui-hooks.c b/gdb/tui/tui-hooks.c
index efa02e2f08a..9a8f2edac38 100644
--- a/gdb/tui/tui-hooks.c
+++ b/gdb/tui/tui-hooks.c
@@ -107,6 +107,26 @@ tui_event_modify_breakpoint (struct breakpoint *b)
   tui_update_all_breakpoint_info ();
 }
 
+
+/* Cache the last state of the TUI display, so that we can tell if
+   something has changed.  In particular, if the frame changed, or if
+   the PC changed, or if the current inferior changed, then the
+   display will update.  Otherwise, it will not.  This caching is
+   needed to let "list" affect the source window display without
+   resetting.  See PR tui/18932.  */
+static struct frame_id last_frame_id = null_frame_id;
+static CORE_ADDR last_frame_pc = 0;
+static inferior *last_inferior = nullptr;
+
+/* Clear the inferior cache when the inferior is destroyed.  */
+
+static void
+clear_inferior_cache (inferior *inf)
+{
+  if (last_inferior == inf)
+    last_inferior = nullptr;
+}
+
 /* Refresh TUI's frame and register information.  This is a hook intended to be
    used to update the screen after potential frame and register changes.
 
@@ -117,36 +137,55 @@ static void
 tui_refresh_frame_and_register_information (int registers_too_p)
 {
   struct frame_info *fi;
-  CORE_ADDR pc;
-  int frame_info_changed_p;
+  CORE_ADDR pc = 0;
+  int frame_info_changed_p = 0;
 
   if (!has_stack_frames ())
-    return;
+    {
+      last_frame_id = null_frame_id;
+      last_frame_pc = 0;
+      last_inferior = nullptr;
+      return;
+    }
 
   target_terminal::scoped_restore_terminal_state term_state;
   target_terminal::ours_for_output ();
 
   fi = get_selected_frame (NULL);
-  /* Ensure that symbols for this frame are read in.  Also, determine
-     the source language of this frame, and switch to it if
-     desired.  */
-  if (get_frame_pc_if_available (fi, &pc))
+  bool have_pc = get_frame_pc_if_available (fi, &pc);
+
+  struct frame_id fid = get_frame_id (fi);
+  if ((!frame_id_p (last_frame_id)
+       || !frame_id_eq (last_frame_id, fid)
+       || pc != last_frame_pc
+       || current_inferior () != last_inferior))
     {
-      struct symtab *s;
-
-      s = find_pc_line_symtab (pc);
-      /* elz: This if here fixes the problem with the pc not being
-	 displayed in the tui asm layout, with no debug symbols.  The
-	 value of s would be 0 here, and select_source_symtab would
-	 abort the command by calling the 'error' function.  */
-      if (s)
-	select_source_symtab (s);
+      /* Display the frame position (even if there is no symbols or
+	 the PC is not known).  */
+
+      last_frame_id = fid;
+      last_frame_pc = pc;
+      last_inferior = current_inferior ();
+
+      /* Ensure that symbols for this frame are read in.  Also, determine
+	 the source language of this frame, and switch to it if
+	 desired.  */
+      if (have_pc)
+	{
+	  struct symtab *s;
+
+	  s = find_pc_line_symtab (pc);
+	  /* elz: This if here fixes the problem with the pc not being
+	     displayed in the tui asm layout, with no debug symbols.  The
+	     value of s would be 0 here, and select_source_symtab would
+	     abort the command by calling the 'error' function.  */
+	  if (s)
+	    select_source_symtab (s);
+	}
+
+      frame_info_changed_p = tui_show_frame_info (fi);
     }
 
-  /* Display the frame position (even if there is no symbols or the PC
-     is not known).  */
-  frame_info_changed_p = tui_show_frame_info (fi);
-
   /* Refresh the register window if it's visible.  */
   if (tui_is_window_visible (DATA_WIN)
       && (frame_info_changed_p || registers_too_p))
@@ -271,4 +310,5 @@ _initialize_tui_hooks (void)
 {
   /* Install the permanent hooks.  */
   gdb::observers::new_objfile.attach (tui_new_objfile_hook);
+  gdb::observers::inferior_removed.attach (clear_inferior_cache);
 }
-- 
2.13.6