help-C-file-name shouldn't error out if we can't find the name

* lisp/help-fns.el (help-C-file-name): Make help-C-file-name
return nil instead of signalling an error if we can't find the
file name (bug#17250).

Copyright-paperwork-exempt: yes

1 files changed, 20 insertions, 14 deletions

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 949def1bbe7..baef5a789ae 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -196,7 +196,8 @@ When called from lisp, FUNCTION may also be a function object."
 ;;;###autoload
 (defun help-C-file-name (subr-or-var kind)
   "Return the name of the C file where SUBR-OR-VAR is defined.
-KIND should be `var' for a variable or `subr' for a subroutine."
+KIND should be `var' for a variable or `subr' for a subroutine.
+If we can't find the file name, nil is returned."
   (let ((docbuf (get-buffer-create " *DOC*"))
         (name (if (eq 'var kind)
                   (concat "V" (symbol-name subr-or-var))
@@ -208,19 +209,24 @@ KIND should be `var' for a variable or `subr' for a subroutine."
            (expand-file-name internal-doc-file-name doc-directory)))
       (let ((file (catch 'loop
                     (while t
-                      (let ((pnt (search-forward (concat "\^_" name "\n"))))
-                        (re-search-backward "\^_S\\(.*\\)")
-                        (let ((file (match-string 1)))
-                          (if (member file build-files)
-                              (throw 'loop file)
-                            (goto-char pnt))))))))
-        (if (string-match "^ns.*\\(\\.o\\|obj\\)\\'" file)
-            (setq file (replace-match ".m" t t file 1))
-          (if (string-match "\\.\\(o\\|obj\\)\\'" file)
-              (setq file (replace-match ".c" t t file))))
-        (if (string-match "\\.\\(c\\|m\\)\\'" file)
-            (concat "src/" file)
-          file)))))
+                      (let ((pnt (search-forward (concat "\^_" name "\n")
+                                                 nil t)))
+                        (if (not pnt)
+                            (throw 'loop nil)
+                          (re-search-backward "\^_S\\(.*\\)")
+                          (let ((file (match-string 1)))
+                            (if (member file build-files)
+                                (throw 'loop file)
+                              (goto-char pnt)))))))))
+        (if (not file)
+            nil
+          (if (string-match "^ns.*\\(\\.o\\|obj\\)\\'" file)
+              (setq file (replace-match ".m" t t file 1))
+            (if (string-match "\\.\\(o\\|obj\\)\\'" file)
+                (setq file (replace-match ".c" t t file))))
+          (if (string-match "\\.\\(c\\|m\\)\\'" file)
+              (concat "src/" file)
+            file))))))
 
 (defcustom help-downcase-arguments nil
   "If non-nil, argument names in *Help* buffers are downcased."