[slime-devel] Strange behavior in edit-definition

[Antonio Menezes Leitao]

Hi all,

I've been experiencing some strange bugs related to the
slime-show-xrefs function trying to access the 'void variable'
package.  This behavior occurs more or less consistently while editing
(on a Linux machine) a set of files that where written using the Franz
Emacs Lisp Interface on a MacOSX.

Here is one example of the stacktrace:

Debugger entered--Lisp error: (void-variable package)
  (slime-init-xref-buffer package G88189 G88190)
  (progn (slime-init-xref-buffer package G88189 G88190) (make-local-variable (quote slime-xref-saved-window-configuration)) (setq slime-xref-saved-window-configuration (current-window-configuration)))
  (prog2 (progn (slime-init-xref-buffer package G88189 G88190) (make-local-variable ...) (setq slime-xref-saved-window-configuration ...)) (progn (slime-insert-xrefs xrefs) (goto-char ...) (forward-line) (skip-chars-forward " 	")) (setq buffer-read-only t) (select-window (or ... ...)) (shrink-window-if-larger-than-buffer))
  (save-current-buffer (set-buffer (get-buffer-create ...)) (prog2 (progn ... ... ...) (progn ... ... ... ...) (setq buffer-read-only t) (select-window ...) (shrink-window-if-larger-than-buffer)))
  (with-current-buffer (get-buffer-create (format "*XREF[%s: %s]*" G88189 G88190)) (prog2 (progn ... ... ...) (progn ... ... ... ...) (setq buffer-read-only t) (select-window ...) (shrink-window-if-larger-than-buffer)))
  (let ((G88189 type) (G88190 symbol)) (with-current-buffer (get-buffer-create ...) (prog2 ... ... ... ... ...)))
  (slime-with-xref-buffer (package type symbol) (slime-insert-xrefs xrefs) (goto-char (point-min)) (forward-line) (skip-chars-forward " 	"))
  (if (null xrefs) (message "No references found for %s." symbol) (setq slime-next-location-function (quote slime-goto-next-xref)) (slime-with-xref-buffer (package type symbol) (slime-insert-xrefs xrefs) (goto-char ...) (forward-line) (skip-chars-forward " 	")))
  slime-show-xrefs((("expression-right-operand" ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INFIX-EXPRESSION)))" :location ... ... nil) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INSTANCEOF-EXPRESSION)))" :location ... ... nil) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND :AROUND (NODE)))" :location ... ... nil) ("(:OPERATOR EXPRESSION-RIGHT-OPERAND)" :location ... ... nil))) definition "expression-right-operand" ":jnil")
  slime-show-definitions("expression-right-operand" (("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INFIX-EXPRESSION)))" (:location ... ... nil)) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INSTANCEOF-EXPRESSION)))" (:location ... ... nil)) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND :AROUND (NODE)))" (:location ... ... nil)) ("(:OPERATOR EXPRESSION-RIGHT-OPERAND)" (:location ... ... nil))))
  (if (slime-length> definitions 1) (slime-show-definitions name definitions) (let (...) (destructure-case ... ... ...)))
  slime-goto-definition("expression-right-operand" (("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INFIX-EXPRESSION)))" (:location ... ... nil)) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND (INSTANCEOF-EXPRESSION)))" (:location ... ... nil)) ("(:OPERATOR (METHOD EXPRESSION-RIGHT-OPERAND :AROUND (NODE)))" (:location ... ... nil)) ("(:OPERATOR EXPRESSION-RIGHT-OPERAND)" (:location ... ... nil))) nil)
  (if (null definitions) (if slime-edit-definition-fallback-function (funcall slime-edit-definition-fallback-function name) (error "No known definition for: %s" name)) (slime-goto-definition name definitions where))
  (let ((definitions ...)) (if (null definitions) (if slime-edit-definition-fallback-function ... ...) (slime-goto-definition name definitions where)))
  slime-edit-definition("expression-right-operand")
  call-interactively(slime-edit-definition)

Here is (what I think is) the relevant function:

(defun slime-show-xrefs (xrefs type symbol package)
  "Show the results of an XREF query."
  (if (null xrefs)
      (message "No references found for %s." symbol)
    (setq slime-next-location-function 'slime-goto-next-xref)
    (slime-with-xref-buffer (package type symbol)
      (slime-insert-xrefs xrefs)
      (goto-char (point-min))
      (forward-line)
      (skip-chars-forward " \t"))))

This function uses the macro slime-with-xref-buffer:

(defmacro* slime-with-xref-buffer ((package ref-type symbol) &body body)
  "Execute BODY in a xref buffer, then show that buffer."
  (let ((type (gensym))
        (sym (gensym)))
    `(let ((,type ,ref-type)
           (,sym ,symbol))
       (with-current-buffer (get-buffer-create 
                             (format "*XREF[%s: %s]*" ,type ,sym))
         (prog2 (progn
                  (slime-init-xref-buffer ,package ,type ,sym)
                  (make-local-variable 'slime-xref-saved-window-configuration)
                  (setq slime-xref-saved-window-configuration
                        (current-window-configuration)))
             (progn , at body)
           (setq buffer-read-only t)
           (select-window (or (get-buffer-window (current-buffer) t)
                              (display-buffer (current-buffer) t)))
           (shrink-window-if-larger-than-buffer))))))

I confess that I couldn't identify the cause for the bug.  However, I
noticed that the macrocall expands into a

(with-current-buffer ... (slime-init-xref-buffer package ...))

and maybe it was that 'package' variable being referenced after
changing to a different buffer that was causing the problem.  An hard
to believe explanation, I'm sure, but just in case, I experimented
replacing that 'package' variable by another gensym, using:

(defmacro* slime-with-xref-buffer ((package ref-type symbol) &body body)
  "Execute BODY in a xref buffer, then show that buffer."
  (let ((type (gensym))
        (sym (gensym))
        (pkg (gensym)))
    `(let ((,type ,ref-type)
           (,sym ,symbol)
           (,pkg ,package))
       (with-current-buffer (get-buffer-create 
                             (format "*XREF[%s: %s]*" ,type ,sym))
         (prog2 (progn
                  (slime-init-xref-buffer ,pkg ,type ,sym)
                  (make-local-variable 'slime-xref-saved-window-configuration)
                  (setq slime-xref-saved-window-configuration
                        (current-window-configuration)))
             (progn , at body)
           (setq buffer-read-only t)
           (select-window (or (get-buffer-window (current-buffer) t)
                              (display-buffer (current-buffer) t)))
           (shrink-window-if-larger-than-buffer))))))

and after redefining slime-show-xrefs, everything worked OK.

Maybe a Slime expert can understand the problem.

Best regards,

António Leitão.