[gdb/tui] Fix centering and highlighting of current line

After starting TUI like this with a hello world a.out:
...
$ gdb -q a.out -ex start -ex "tui enable"
...
we get:
...
┌─hello.c──────────────────────────────┐
│        5 {                           │
│        6   printf ("hello\n");       │
│        7                             │
│        8   return 0;                 │
│        9 }                           │
│                                      │
└──────────────────────────────────────┘
...

This is a regression since commit ee1e9bbb513 ("[gdb/tui] Fix displaying main
after resizing"), before which we had instead:
...
┌─hello.c──────────────────────────────┐
│        4 main (void)                 │
│        5 {                           │
│  >     6   printf ("hello\n");       │
│        7                             │
│        8   return 0;                 │
│        9 }                           │
└──────────────────────────────────────┘
...

In other words, the problems are:
- the active line (source line 6) is no longer highlighted, and
- the active line is not vertically centered (screen line 2 out 6 instead of
  screen line 3 out of 6).

Fix these problems respectively by:
- in tui_enable, instead of "tui_show_frame_info (0)" using
  'tui_show_frame_info (deprecated_safe_get_selected_frame ())", and
- in tui_source_window_base::rerender, adding centering functionality.

Tested on aarch64-linux.

Co-Authored-By: Tom Tromey <tom@tromey.com>
Approved-By: Tom Tromey <tom@tromey.com>

PR tui/31522
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31522

2 files changed, 11 insertions, 1 deletions

diff --git a/gdb/tui/tui-winsource.c b/gdb/tui/tui-winsource.c
index 4dbbe92..61c8e00 100644
--- a/gdb/tui/tui-winsource.c
+++ b/gdb/tui/tui-winsource.c
@@ -467,6 +467,16 @@ tui_source_window_base::rerender ()
       struct symtab *s = find_pc_line_symtab (get_frame_pc (frame));
       if (this != TUI_SRC_WIN)
 	find_line_pc (s, cursal.line, &cursal.pc);
+
+      /* This centering code is copied from tui_source_window::maybe_update.
+	 It would be nice to do centering more often, and do it in just one
+	 location.  But since this is a regression fix, handle this
+	 conservatively for now.  */
+      int start_line = (cursal.line - ((height - box_size ()) / 2)) + 1;
+      if (start_line <= 0)
+	start_line = 1;
+      cursal.line = start_line;
+
       update_source_window (gdbarch, cursal);
     }
   else
diff --git a/gdb/tui/tui.c b/gdb/tui/tui.c
index 19f0960..eaee85f 100644
--- a/gdb/tui/tui.c
+++ b/gdb/tui/tui.c
@@ -466,7 +466,7 @@ tui_enable (void)
       tui_set_term_width_to (COLS);
       def_prog_mode ();
 
-      tui_show_frame_info (0);
+      tui_show_frame_info (deprecated_safe_get_selected_frame ());
       tui_set_initial_layout ();
       tui_set_win_focus_to (TUI_SRC_WIN);
       keypad (TUI_CMD_WIN->handle.get (), TRUE);