Be defensive against missing primitive source code

If find-function-C-source-directory isn't set, or if it's set to a
directory that contains source to a different Emacs version, just
return nil from helpful--definition.

2 files changed, 9 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 11dfdab..22851a9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@
 Fixed a crash on functions defined in a .elc when the .el file is not
 available.
 
+Fixed some crashes on primitive functions.
+
 Better handling of docstrings:
 
 * All strings in quotes are highlighted. For example, previously
diff --git a/helpful.el b/helpful.el
index 711bb7f..640d408 100644
--- a/helpful.el
+++ b/helpful.el
@@ -790,7 +790,7 @@ buffer."
         ;; `base-sym' is the underlying symbol if `sym' is an alias.
         (setq sym base-sym)
         (setq path src-path)))
-    (when (and primitive-p path)
+    (when (and primitive-p path find-function-C-source-directory)
       ;; Convert "src/foo.c" to "".
       (setq path (f-expand path
                            (f-parent find-function-C-source-directory))))
@@ -849,7 +849,12 @@ buffer."
           (-let [(sym-buf . sym-pos) (find-definition-noselect sym 'defvar)]
             (setq buf sym-buf)
             (setq pos sym-pos))
-        (search-failed nil))))
+        (search-failed nil)
+        ;; If your current Emacs instance doesn't match the source
+        ;; code configured in find-function-C-source-directory, we can
+        ;; get an error about not finding source. Try
+        ;; `default-tab-width' against Emacs trunk.
+        (error nil))))
     (list buf pos opened)))
 
 (defun helpful--source-path (sym callable-p)