Handle byte-compiled functions bound to keys

Fixes #212

3 files changed, 24 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5432d85..fef5657 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ Show the original value for custom variables whose value has changed.
 
 Report the package version when custom variables were added.
 
+Fixed a crash on assigning byte-compiled objects to keybindings.
+
 # v0.17
 
 Fixed a minor docstring formatting issue when keymap references were
diff --git a/helpful.el b/helpful.el
index 1cff11b..7a71f4e 100644
--- a/helpful.el
+++ b/helpful.el
@@ -2373,9 +2373,14 @@ For example, \"(some-func FOO &optional BAR)\"."
            (gethash (symbol-function sym) advertised-signature-table))))
     ;; Get the usage from the function definition.
     (let* ((function-args
-            (if (symbolp sym)
-                (help-function-arglist sym)
-              (cadr sym)))
+            (cond
+             ((symbolp sym)
+              (help-function-arglist sym))
+             ((byte-code-function-p sym)
+              (aref sym 0))
+             (t
+              ;; Interpreted function (lambda ...)
+              (cadr sym))))
            (formatted-args
             (cond
              (advertised-args
diff --git a/test/helpful-unit-test.el b/test/helpful-unit-test.el
index 14d44dc..596bd8c 100644
--- a/test/helpful-unit-test.el
+++ b/test/helpful-unit-test.el
@@ -533,6 +533,20 @@ associated a lambda with a keybinding."
     (with-current-buffer buf
       (helpful-update))))
 
+(ert-deftest helpful--unnamed-compiled-func ()
+  "Ensure we handle unnamed byte-compiled functions.
+
+This is important for `helpful-key', where a user may have
+associated a lambda with a keybinding."
+  (let* ((fun (byte-compile (lambda (x) x)))
+         (buf (helpful--buffer fun t)))
+    ;; There's no name, so just show lambda in the buffer name.
+    (should
+     (equal (buffer-name buf) "*helpful lambda*"))
+    ;; Don't crash when we show the buffer.
+    (with-current-buffer buf
+      (helpful-update))))
+
 (ert-deftest helpful--obsolete-variable ()
   "Test display of obsolete variable."
   (let* ((var 'helpful-test-var-obsolete)