patch 8.1.1880: cannot show extra info for completion in a popup window

Problem:    Cannot show extra info for completion in a popup window.
Solution:   Add the "popup" entry in 'completeopt'.

src/popupwin.c

@@ -951,8 +951,8 @@ popup_top_extra(win_T *wp)
 popup_height(win_T *wp)
 {
     return wp->w_height
-	+ popup_top_extra(wp)
-	+ wp->w_popup_padding[2] + wp->w_popup_border[2];
+	    + popup_top_extra(wp)
+	    + wp->w_popup_padding[2] + wp->w_popup_border[2];
 }
 
 /*
@@ -965,10 +965,19 @@ popup_width(win_T *wp)
     // w_leftcol is how many columns of the core are left of the screen
     // w_popup_rightoff is how many columns of the core are right of the screen
     return wp->w_width + wp->w_leftcol
-	+ wp->w_popup_padding[3] + wp->w_popup_border[3]
-	+ wp->w_popup_padding[1] + wp->w_popup_border[1]
-	+ wp->w_has_scrollbar
-	+ wp->w_popup_rightoff;
+	    + popup_extra_width(wp)
+	    + wp->w_popup_rightoff;
+}
+
+/*
+ * Return the extra width of popup window "wp": border, padding and scrollbar.
+ */
+    int
+popup_extra_width(win_T *wp)
+{
+    return wp->w_popup_padding[3] + wp->w_popup_border[3]
+	    + wp->w_popup_padding[1] + wp->w_popup_border[1]
+	    + wp->w_has_scrollbar;
 }
 
 /*
@@ -1230,7 +1239,8 @@ typedef enum
     TYPE_NOTIFICATION,
     TYPE_DIALOG,
     TYPE_MENU,
-    TYPE_PREVIEW
+    TYPE_PREVIEW,	// preview window
+    TYPE_INFO		// popup menu info
 } create_type_T;
 
 /*
@@ -1330,7 +1340,7 @@ parse_previewpopup(win_T *wp)
  * Keep at least "width" columns from the right of the screen.
  */
     void
-popup_set_wantpos(win_T *wp, int width)
+popup_set_wantpos_cursor(win_T *wp, int width)
 {
     setcursor_mayforce(TRUE);
     wp->w_wantline = curwin->w_winrow + curwin->w_wrow;
@@ -1350,11 +1360,38 @@ popup_set_wantpos(win_T *wp, int width)
     popup_adjust_position(wp);
 }
 
+/*
+ * Set w_wantline and w_wantcol for the a given screen position.
+ * Caller must take care of running into the window border.
+ */
+    void
+popup_set_wantpos_rowcol(win_T *wp, int row, int col)
+{
+    wp->w_wantline = row;
+    wp->w_wantcol = col;
+    popup_adjust_position(wp);
+}
+
+/*
+ * Add a border and lef&right padding.
+ */
+    static void
+add_border_left_right_padding(win_T *wp)
+{
+    int i;
+
+    for (i = 0; i < 4; ++i)
+    {
+	wp->w_popup_border[i] = 1;
+	wp->w_popup_padding[i] = (i & 1) ? 1 : 0;
+    }
+}
+
 /*
  * popup_create({text}, {options})
  * popup_atcursor({text}, {options})
  * etc.
- * When creating a preview window popup "argvars" and "rettv" are NULL.
+ * When creating a preview or info popup "argvars" and "rettv" are NULL.
  */
     static win_T *
 popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
@@ -1495,7 +1532,7 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
     }
     if (type == TYPE_ATCURSOR)
     {
-	popup_set_wantpos(wp, 0);
+	popup_set_wantpos_cursor(wp, 0);
 	set_moved_values(wp);
 	set_moved_columns(wp, FIND_STRING);
     }
@@ -1571,11 +1608,7 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	wp->w_zindex = POPUPWIN_DIALOG_ZINDEX;
 	wp->w_popup_flags |= POPF_DRAG;
 	wp->w_popup_flags &= ~POPF_MAPPING;
-	for (i = 0; i < 4; ++i)
-	{
-	    wp->w_popup_border[i] = 1;
-	    wp->w_popup_padding[i] = (i & 1) ? 1 : 0;
-	}
+	add_border_left_right_padding(wp);
     }
 
     if (type == TYPE_MENU)
@@ -1600,7 +1633,14 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	for (i = 0; i < 4; ++i)
 	    wp->w_popup_border[i] = 1;
 	parse_previewpopup(wp);
-	popup_set_wantpos(wp, wp->w_minwidth);
+	popup_set_wantpos_cursor(wp, wp->w_minwidth);
+    }
+    if (type == TYPE_INFO)
+    {
+	wp->w_popup_pos = POPPOS_TOPLEFT;
+	wp->w_popup_flags |= POPF_DRAG | POPF_RESIZE;
+	wp->w_popup_close = POPCLOSE_BUTTON;
+	add_border_left_right_padding(wp);
     }
 
     for (i = 0; i < 4; ++i)
@@ -3171,6 +3211,28 @@ popup_find_preview_window(void)
     return NULL;
 }
 
+    int
+popup_is_popup(win_T *wp)
+{
+    return wp->w_popup_flags != 0;
+}
+
+/*
+ * Find an existing popup used as the info window, in the current tab page.
+ * Return NULL if not found.
+ */
+    win_T *
+popup_find_info_window(void)
+{
+    win_T *wp;
+
+    // info window popup is always local to tab page.
+    for (wp = curtab->tp_first_popupwin; wp != NULL; wp = wp->w_next)
+	if (wp->w_popup_flags & POPF_INFO)
+	    return wp;
+    return NULL;
+}
+
     void
 f_popup_getpreview(typval_T *argvars UNUSED, typval_T *rettv)
 {
@@ -3179,26 +3241,23 @@ f_popup_getpreview(typval_T *argvars UNUSED, typval_T *rettv)
     rettv->vval.v_number = wp == NULL ? 0 : wp->w_id;
 }
 
-    int
-popup_is_popup(win_T *wp)
-{
-    return wp->w_popup_flags != 0;
-}
-
 /*
- * Create a popup to be used as the preview window.
+ * Create a popup to be used as the preview or info window.
  * NOTE: this makes the popup the current window, so that the file can be
  * edited.  However, it must not remain to be the current window, the caller
  * must make sure of that.
  */
     int
-popup_create_preview_window(void)
+popup_create_preview_window(int info)
 {
-    win_T *wp = popup_create(NULL, NULL, TYPE_PREVIEW);
+    win_T *wp = popup_create(NULL, NULL, info ? TYPE_INFO : TYPE_PREVIEW);
 
     if (wp == NULL)
 	return FAIL;
-    wp->w_p_pvw = TRUE;
+    if (info)
+	wp->w_popup_flags |= POPF_INFO;
+    else
+	wp->w_p_pvw = TRUE;
 
     // Set the width to a reasonable value, so that w_topline can be computed.
     if (wp->w_minwidth > 0)
@@ -3216,9 +3275,9 @@ popup_create_preview_window(void)
 }
 
     void
-popup_close_preview()
+popup_close_preview(int info)
 {
-    win_T *wp = popup_find_preview_window();
+    win_T *wp = info ? popup_find_info_window() : popup_find_preview_window();
 
     if (wp != NULL)
     {