Ensure that we handle interactively defined functions

Also add a test

2 files changed, 10 insertions, 4 deletions

diff --git a/helpful.el b/helpful.el
index b69c509..11676da 100644
--- a/helpful.el
+++ b/helpful.el
@@ -400,10 +400,11 @@ for killing the newly created buffer."
       ;;
       ;; Narrowing has been fixed upstream:
       ;; http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=abd18254aec76b26e86ae27e91d2c916ec20cc46
-      (-let* (((base-sym . path) (find-function-library sym))
-              (src-buf (find-file-noselect path)))
-        (with-current-buffer src-buf
-          ;; Ignore the current narrowing and point position in `src-buf'.
+      (-when-let ((base-sym . path) (find-function-library sym))
+        ;; Open `path' ourselves. If the user has already opened it,
+        ;; we ensure that we don't change their narrowing or point
+        ;; position when we search it.
+        (with-current-buffer (find-file-noselect path)
           (save-excursion
             (save-restriction
               (widen)
diff --git a/test/unit-test.el b/test/unit-test.el
index 88602d3..cf50f35 100644
--- a/test/unit-test.el
+++ b/test/unit-test.el
@@ -40,6 +40,11 @@
   "We should not crash on a function without a docstring."
   (should (null (helpful--docstring #'test-foo-no-docstring t))))
 
+(ert-deftest helpful--interacively-defined-fn ()
+  "We should not crash on a function without source code."
+  (eval '(defun test-foo-defined-interactively () 42))
+  (helpful-function #'test-foo-defined-interactively))
+
 (defun test-foo-usage-docstring ()
   "\n\n(fn &rest ARGS)"
   nil)