Type error in example prefix `tsc-lisp-variable`

[YHN-ice]

The error is produced under transient version 0.8.7 (afc88b2)

Related Codes

transient-showcase/transient-showcase.el

Lines 588 to 613 in ac2bbe6

	(defvar tsc--position '(0 0) "A transient prefix location.")
	(transient-define-infix tsc--pos-infix ()
	"A location, key, or command symbol."
	:class 'transient-lisp-variable
	:transient t
	:prompt "An expression such as (0 0), \"p\", nil, 'tsc--msg-pos: "
	:variable 'tsc--position)
	(transient-define-suffix tsc--msg-pos ()
	"Message the element at location."
	:transient 'transient--do-call
	(interactive)
	;; lisp variables are not sent in the usual (transient-args) list.
	;; Just read `tsc--position' directly.
	(let ((suffix (transient-get-suffix
	transient-current-command tsc--position)))
	(message "%s" (oref suffix description))))
	(transient-define-prefix tsc-lisp-variable ()
	"A prefix that updates and uses a lisp variable."
	["Location Printing"
	[("p" "position" tsc--pos-infix)]
	[("m" "message" tsc--msg-pos)]])
	;; (tsc-lisp-variable)

Errors

In this example that uses transient-get-suffix, when running with loc (0 0) it errors with

message: Wrong type argument: (or eieio-object cl-structure-object oclosure), [nil transient-column nil ((nil transient-suffix (:key "p" :description "position" :command tsc--pos-infix)))] 

It locates a column. To pick a suffix, use (0 0 0). But it errors with

message: Wrong type argument: (or eieio-object cl-structure-object oclosure), (nil transient-suffix (:key "p" :description "position" :command tsc--pos-infix))

Root Cause

Turns out that the function returns a list of form (LEVEL CLASS PLIST) rather than the ones oref expects, see transient.org from transient

https://github.com/magit/transient/blob/afc88b24e4faa5c7e246303648e70b4507652f32/docs/transient.org?plain=1#L861-L864

Proposed Change

By change the way of accessing suffix (see the implement of transient-suffix-put at https://github.com/magit/transient/blob/afc88b24e4faa5c7e246303648e70b4507652f32/lisp/transient.el#L1564-L1566), it message the desired slot value.

     (message "%s" (plist-get (elt suffix 2) :description)))) 

[psionic-k]

Those addresses, (0 0 0) and (0 0) or even (0) etc can point to different elements. If you poke around, there might be more errors. Probably an if statement is necessary to react usefully in every case.

[YHN-ice]

If you meant better error handling against unexpected user input, I guess the following code would work as you expected?

1 file changed, 4 insertions(+), 1 deletion(-)                                                                                                                                                        
transient-showcase.el | 5 ++++-                                                                                                                                                                       
                                                                                                                                                                                                      
modified   transient-showcase.el                                                                                                                                                                      
@@ -602,7 +602,10 @@ This uses the short interactive code."                                                                                                                                           
   ;; Just read `tsc--position' directly.                                                                                                                                                             
   (let ((suffix (transient-get-suffix                                                                                                                                                                
                  transient-current-command tsc--position)))                                                                                                                                          
-    (message "%s" (oref suffix description))))                                                                                                                                                       
+                                                                                                                                                                                                     
+    (if (and (listp suffix) (eq (elt suffix 1) 'transient-suffix))                                                                                                                                   
+        (message "%s" (plist-get (elt suffix 2) :description))                                                                                                                                       
+      (message "located element is not transient-suffix"))))                                                                                                                                         
                                                                                                                                                                                                      
 (transient-define-prefix tsc-lisp-variable ()                                                                                                                                                        
   "A prefix that updates and uses a lisp variable."