bug#30564: call-process always fails for empty exec-path

bug#30564: call-process always fails for empty exec-path

[Christopher Wellons]

The call-process function incorrectly fails for valid absolute paths 
when exec-path is nil:

    (let ((exec-path ()))
      (call-process "/bin/ls"))
    ;; error: (file-error "Searching for program"
    ;;                    "No such file or directory" "/bin/ls")

Adding a single element to exec-path fixes the problem, even if that 
element is nonsense:

    (let ((exec-path '(t)))
      (call-process "/bin/ls"))
    ;; => 0

The bug is in the for loop in openp() (lread.c). The only successful 
returns are found inside the loop. An empty list results in no loop 
iterations, which means an absolute path has no chance to return 
successfully.

This bug dates back at least as far as Emacs 24.3.

bug#30564: call-process always fails for empty exec-path

[Lars Ingebrigtsen]

Christopher Wellons <wellons@nullprogram.com> writes:

> The call-process function incorrectly fails for valid absolute paths
> when exec-path is nil:
>
>    (let ((exec-path ()))
>      (call-process "/bin/ls"))
>    ;; error: (file-error "Searching for program"
>    ;;                    "No such file or directory" "/bin/ls")
>
> Adding a single element to exec-path fixes the problem, even if that
> element is nonsense:
>
>    (let ((exec-path '(t)))
>      (call-process "/bin/ls"))
>    ;; => 0
>
> The bug is in the for loop in openp() (lread.c). The only successful
> returns are found inside the loop. An empty list results in no loop
> iterations, which means an absolute path has no chance to return
> successfully.

I've now fixed this by transforming the for loop into a do/while loop.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no