bug#38248: help-follow-symbol silent when no symbol was found

[Juanma Barranquero <lekktu@gmail.com>]

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Package: emacs
Severity: minor
Tags: patch

Currently, help-follow and help-follow-mouse signal an error if there's
nothing to follow. However, help-follow-symbol does not, which means that
C-c C-c in the help buffer when over an arbitrary non-symbol does nothing
and says nothing.

That's not just inconsistent, but a bit disconcerting, as sometimes
following a symbol can be slow. In my build, it takes a second or more to
show the symbol documentation, so when there's no symbol I stand waiting
for something to happen for a couple of seconds.

The following patch fixes that. The only reason against I can think of is
when `help-follow-symbol' is called from elisp, because it will now signal
an error. However, at least in the Emacs sources help-follow-symbol is
never called from elisp, just as a keybinding or menu entry.

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From 4fb8e8c124009ab283fb9d15ad7aaa0a90f56ec7 Mon Sep 17 00:00:00 2001
From: Juanma Barranquero <lekktu@gmail.com>
Date: Sun, 17 Nov 2019 20:27:12 +0100
Subject: [PATCH] * lisp/help-mode.el (help-follow-symbol): Signal no symbol at
 point.

---
 lisp/help-mode.el | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lisp/help-mode.el b/lisp/help-mode.el
index 054a1ef8c2..e70570c3ee 100644
--- a/lisp/help-mode.el
+++ b/lisp/help-mode.el
@@ -749,10 +749,11 @@ help-follow-symbol
 	    (buffer-substring (point)
 			      (progn (skip-syntax-forward "w_")
 				     (point)))))))
-    (when (or (boundp sym)
-	      (get sym 'variable-documentation)
-	      (fboundp sym) (facep sym))
-      (help-do-xref pos #'describe-symbol (list sym)))))
+    (if (or (boundp sym)
+	    (get sym 'variable-documentation)
+	    (fboundp sym) (facep sym))
+        (help-do-xref pos #'describe-symbol (list sym))
+      (user-error "No symbol here"))))
 
 (defun help-mode-revert-buffer (_ignore-auto noconfirm)
   (when (or noconfirm (yes-or-no-p "Revert help buffer? "))
-- 
2.23.0.windows.1