tabpage: track last-used tabpage #11626

In a multi-window scenario, it is possible to return focus to the last
accessed window via n_CTRL-W_p.  However, in the case of a multi-tab
scenario, there was previously no way to return focus to the last
accessed *tab*.  Here, that ability is added via n_g<tab>.

Additionally, the index of the previous tab is exposed via
tabpagenr('#'), mirroring the existing functionality of winnr('#').

src/nvim/eval.c

@@ -18172,6 +18172,10 @@ static void f_tabpagenr(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     if (arg != NULL) {
       if (strcmp(arg, "$") == 0) {
         nr = tabpage_index(NULL) - 1;
+      } else if (strcmp(arg, "#") == 0) {
+        nr = valid_tabpage(lastused_tabpage)
+             ? tabpage_index(lastused_tabpage)
+             : nr;
       } else {
         EMSG2(_(e_invexpr2), arg);
       }

src/nvim/globals.h

@@ -459,6 +459,7 @@ EXTERN frame_T  *topframe;      /* top of the window frame tree */
  * one in the list, "curtab" is the current one.
  */
 EXTERN tabpage_T    *first_tabpage;
+EXTERN tabpage_T    *lastused_tabpage;
 EXTERN tabpage_T    *curtab;
 EXTERN int redraw_tabline INIT(= FALSE);           /* need to redraw tabline */
 

src/nvim/normal.c

@@ -6312,9 +6312,7 @@ static void nv_gomark(cmdarg_T *cap)
   }
 }
 
-/*
- * Handle CTRL-O, CTRL-I, "g;" and "g," commands.
- */
+// Handle CTRL-O, CTRL-I, "g;", "g,", and "CTRL-Tab" commands.
 static void nv_pcmark(cmdarg_T *cap)
 {
   pos_T       *pos;
@@ -6322,11 +6320,16 @@ static void nv_pcmark(cmdarg_T *cap)
   const bool old_KeyTyped = KeyTyped;       // getting file may reset it
 
   if (!checkclearopq(cap->oap)) {
-    if (cap->cmdchar == 'g')
+    if (cap->cmdchar == TAB && mod_mask == MOD_MASK_CTRL) {
+      goto_tabpage_lastused();
+      return;
+    }
+    if (cap->cmdchar == 'g') {
       pos = movechangelist((int)cap->count1);
-    else
+    } else {
       pos = movemark((int)cap->count1);
-    if (pos == (pos_T *)-1) {           /* jump to other file */
+    }
+    if (pos == (pos_T *)-1) {           // jump to other file
       curwin->w_set_curswant = true;
       check_cursor();
     } else if (pos != NULL)                 /* can jump */
@@ -7059,6 +7062,11 @@ static void nv_g_cmd(cmdarg_T *cap)
     if (!checkclearop(oap))
       goto_tabpage(-(int)cap->count1);
     break;
+  case TAB:
+    if (!checkclearop(oap)) {
+      goto_tabpage_lastused();
+    }
+    break;
 
   case '+':
   case '-':   /* "g+" and "g-": undo or redo along the timeline */

src/nvim/window.c

@@ -519,6 +519,10 @@ wingotofile:
       do_nv_ident('g', xchar);
       break;
 
+    case TAB:
+      goto_tabpage_lastused();
+      break;
+
     case 'f':                       /* CTRL-W gf: "gf" in a new tab page */
     case 'F':                       /* CTRL-W gF: "gF" in a new tab page */
       cmdmod.tab = tabpage_index(curtab) + 1;
@@ -3691,6 +3695,10 @@ void free_tabpage(tabpage_T *tp)
   hash_init(&tp->tp_vars->dv_hashtab);
   unref_var_dict(tp->tp_vars);
 
+  if (tp == lastused_tabpage) {
+    lastused_tabpage = NULL;
+  }
+
   xfree(tp->tp_localdir);
   xfree(tp);
 }
@@ -3750,6 +3758,8 @@ int win_new_tabpage(int after, char_u *filename)
 
     tabpage_check_windows(tp);
 
+    lastused_tabpage = tp;
+
     apply_autocmds(EVENT_WINNEW, NULL, NULL, false, curbuf);
     apply_autocmds(EVENT_WINENTER, NULL, NULL, false, curbuf);
     apply_autocmds(EVENT_TABNEW, filename, filename, false, curbuf);
@@ -3976,6 +3986,7 @@ static void enter_tabpage(tabpage_T *tp, buf_T *old_curbuf, int trigger_enter_au
   if (curtab->tp_old_Columns != Columns && starting == 0)
     shell_new_columns();        /* update window widths */
 
+  lastused_tabpage = old_curtab;
 
   /* Apply autocommands after updating the display, when 'rows' and
    * 'columns' have been set correctly. */
@@ -4095,6 +4106,14 @@ void goto_tabpage_tp(tabpage_T *tp, int trigger_enter_autocmds, int trigger_leav
   }
 }
 
+// Go to the last accessed tab page, if there is one.
+void goto_tabpage_lastused(void)
+{
+  if (valid_tabpage(lastused_tabpage)) {
+    goto_tabpage_tp(lastused_tabpage, true, true);
+  }
+}
+
 /*
  * Enter window "wp" in tab page "tp".
  * Also updates the GUI tab.