run-program with :if-ouput-exists :append assumes existing file

[Ingo Krabbe]

* (run-program "/bin/rm" '("/tmp/test"))
#<SB-IMPL::PROCESS :EXITED 0>
* (run-program "/bin/cat" '("/etc/passwd") :output "/tmp/test" :if-output-exists :append)

debugger invoked on a FILE-DOES-NOT-EXIST in thread
#<THREAD "main thread" RUNNING {1004A18433}>:
  The file #P"/tmp/test" does not exist: No such file or directory

restarts (invokable by number or by possibly-abbreviated name):
  0: [CREATE ] Reopen with :if-does-not-exist :create
  1: [CONTINUE ] Retry opening.
  2: [USE-VALUE] Try opening a different file.
  3: [ABORT ] Exit debugger, returning to top level.

(SB-IMPL::FILE-PERROR #P"/tmp/test" 2 FILE-DOES-NOT-EXIST)
0] 0
#<SB-IMPL::PROCESS :EXITED 0>
* (run-program "/bin/cat" '("/etc/passwd") :output "/tmp/test" :if-output-exists :append)
#<SB-IMPL::PROCESS :EXITED 0>
*

Solution: Add :if-does-not-exist :create, when opening the output file in append mode.

SBCL 2.1.4.129.pick.4-88e0ded29

[Ingo Krabbe (ikrabbe-ask)]

The patch is a git diff taken from the current master

[Ingo Krabbe (ikrabbe-ask)]

With the patch applied against the master I get
SBCL 2.2.0.148-3d74cee17-WIP

* (run-program "/bin/rm" '("/tmp/test"))
#<SB-IMPL::PROCESS :EXITED 0>
* (run-program "/bin/cat" '("/etc/passwd") :output "/tmp/test" :if-output-exists :append)
#<SB-IMPL::PROCESS :EXITED 0>

the expected behavior

[Ingo Krabbe (ikrabbe-ask)]

Ok, the final patch used here is far simpler than my fix, but actually does what is expected, so it is the correct solution. Thank you!

[Stas Boukarev (stassats)]

Your fix was not entirely correct, as it passes NIL in other cases, which would make it simply return.

[Ingo Krabbe (ikrabbe-ask)]

On Fri, 21 Jan 2022 16:25:06 -0000
Stas Boukarev <email address hidden> wrote:

> Your fix was not entirely correct, as it passes NIL in other cases,
> which would make it simply return.
>

Ah, yes I haven't read the exact meanings and defaults from the manual.
Going this way is perfect.

"if-does-not-exist---one of :error, :create, or nil. The default is
:error if direction is :input or if-exists is :overwrite or :append;
:create if direction is :output or :io, and if-exists is neither
:overwrite nor :append; or nil when direction is :probe."

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