Make toolbar show keyboard equivalents in its tooltips

* src/keyboard.c (parse_tool_bar_item): Add equivalent key binding to
the tooltip string of toolbar buttons.
* etc/NEWS: Announce it.
* etc/TODO: Remove its entry.  (Bug#36156)

3 files changed, 16 insertions, 2 deletions

diff --git a/etc/NEWS b/etc/NEWS
index f0d7457a627..0cfac248a32 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -125,6 +125,9 @@ This is intended mostly to help developers.
 ** Emacs now requires GTK 2.24 and GTK 3.10 for the GTK 2 and GTK 3
 builds respectively.
 
+---
+** The toolbar now shows the equivalent key binding in its tooltips.
+
 
 * Startup Changes in Emacs 27.1
 
diff --git a/etc/TODO b/etc/TODO
index 273455c386e..34de81b147c 100644
--- a/etc/TODO
+++ b/etc/TODO
@@ -176,8 +176,6 @@ See the 'test' directory for examples.
 ** In Emacs Info, examples of using Customize should be clickable
    and they should create Custom buffers.
 
-** The toolbar should show keyboard equivalents in its tooltips.
-
 ** Add function to redraw the tool bar.
 
 ** Redesign the load-history data structure so it can cope better
diff --git a/src/keyboard.c b/src/keyboard.c
index ab6ca36219d..0d7f124f5f3 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -8297,6 +8297,19 @@ parse_tool_bar_item (Lisp_Object key, Lisp_Object item)
   if (CONSP (get_keymap (PROP (TOOL_BAR_ITEM_BINDING), 0, 1)))
     return 0;
 
+  /* If there is a key binding, add it to the help, which will be
+     displayed as a tooltip for this entry. */
+  Lisp_Object binding = PROP (TOOL_BAR_ITEM_BINDING);
+  Lisp_Object keys = Fwhere_is_internal (binding, Qnil, Qt, Qnil, Qnil);
+  if (!NILP (keys))
+    {
+      AUTO_STRING (beg, "  (");
+      AUTO_STRING (end, ")");
+      Lisp_Object orig = PROP (TOOL_BAR_ITEM_HELP);
+      Lisp_Object desc = Fkey_description (keys, Qnil);
+      set_prop (TOOL_BAR_ITEM_HELP, CALLN (Fconcat, orig, beg, desc, end));
+    }
+
   /* Enable or disable selection of item.  */
   if (!EQ (PROP (TOOL_BAR_ITEM_ENABLED_P), Qt))
     set_prop (TOOL_BAR_ITEM_ENABLED_P,