bug#69436: confused by changing absolute pathname

[Zefram]

The guile(1) command-line interface is documented to take the filename
of a script to execute.  Here's how well it resolves filenames (testing
on Guile 3.0.5):

$ mkdir a
$ cd a
$ echo '(display "ok") (newline)' > ok.scm
$ perl -e 'chdir ".."; while(1) { rename("a", "b"); rename("b", "a"); }' &
[1] 389562
$ guile --no-auto-compile ok.scm
ok
$ guile --no-auto-compile ok.scm
Backtrace:
           0 (primitive-load "/home/zefram/tmp/g0/b/ok.scm")

ERROR: In procedure primitive-load:
In procedure open-file: No such file or directory: 
"/home/zefram/tmp/g0/b/ok.scm"
$ guile --no-auto-compile ok.scm
Backtrace:
           0 (primitive-load "/home/zefram/tmp/g0/a/ok.scm")

ERROR: In procedure primitive-load:
In procedure open-file: No such file or directory: 
"/home/zefram/tmp/g0/a/ok.scm"
$ guile --no-auto-compile ok.scm
;;; Stat of /home/zefram/tmp/g0/b/ok.scm failed:
;;; In procedure stat: No such file or directory: "/home/zefram/tmp/g0/b/ok.scm"
ok
$ guile --no-auto-compile ok.scm
ok

Each time that I invoked guile(1), the filename "ok.scm" given on the
command line unambiguously referred to an extant script file in the
current directory.  Some invocations successfully ran it, but others
got confused.  The confused invocations either entirely fail to run the
script, or produce some extra stderr noise and then run the script.

guile(1) is getting confused because the absolute pathname of the
current directory is changing.  It works out an absolute pathname for
the specified script, and then tries to use that at a time when it may
be stale.  The manifestation of the bug varies from run to run because
it is subject to this race condition.

I use the --no-auto-compile option in my example in order to avoid the
extra noise of guile's caching system.  If caching is allowed to occur
then similar results ensue, but there's extra stderr noise that doesn't
indicate a real problem, and the situation is semantically a bit more
complicated because of the caching.

guile(1) shouldn't need to use an absolute pathname for the script file.
The name given on the command line should be used; relative pathnames
should work.

Debian incarnations of this bug report (two of them because two versions
of Guile are packaged separately):
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1064443
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1064446

-zefram