bug#15425: mktemp - conflicting options affected by ENV

[Assaf Gordon]

Hello,

Not sure if this is a bug or just unintended side-effect, but it caused some 
scripts here to fail and took a while to troubleshoot:
It basically boils down to the interplay between the deprecated "-t" "-p" and "$TMPDIR" 
and "--tmpdir".

===
##
## Problem 1: "-t" and TMPDIR (if non-empty) overrides "--tmpdir"
##
$ TMPDIR= mktemp -u --tmpdir=. -t XXXXXX
./og9G5s
$ TMPDIR=/foo/ mktemp -u --tmpdir=. -t XXXXXX
/foo/AAWcOl

##
## Problem 2: if TMPDIR is empty, "--tmpdir" overrides "-p", despite having "-t"
##
$ TMPDIR=/foo/ mktemp -u -p /bar/ --tmpdir=. -t XXXXXX
/foo/tHXcrq
$ TMPDIR= mktemp -u -p /bar/ --tmpdir=. -t XXXXXX
./OfWXSS
## I'd expect the above to use "/bar/OfWXSS", to be consistent with TMPDIR overriding 
"--tmpdir".
===

I realize "-t" and "-p" are deprecated, and it's best not to meddle with them -
but for consistency, perhaps consider having the new "--tmpdir" always take precedence over 
"-t" and "-p" ?
or print a warning to STDERR when "-t" and "--tmpdir" are mixed?

Regards,
 -gordon