tests: fix false fails due to passing env vars to returns_

On BSD /bin/sh it was seen that unexported env vars passed to
returns_() would not be propagated to the wrapped command.

* cfg.mk (sc_prohibit_env_returns): Add a syntax check to disallow.
* tests/misc/csplit-io-err.sh: Rearrange to export vars in a subshell.
* tests/rm/rm-readdir-fail.sh: Likewise.
* tests/misc/nohup.sh: Export and unset vars around returns_.
* tests/misc/printenv.sh: Likewise.
Reported by Assaf Gordon

cfg.mk

@@ -510,6 +510,14 @@ sc_prohibit_and_fail_1:
 	in_vc_files='^tests/'						\
 	  $(_sc_search_regexp)
 
+# Ensure that env vars are not passed through returns_ as
+# that was seen to fail on FreeBSD /bin/sh at least
+sc_prohibit_env_returns:
+	@prohibit='=[^ ]* returns_ '					\
+	halt='Passing env vars to returns_ is non portable'		\
+	in_vc_files='^tests/'						\
+	  $(_sc_search_regexp)
+
 # The mode part of a setfacl -m option argument must be three bytes long.
 # I.e., an argument of user:bin:rw or user:bin:r will make Solaris 10's
 # setfacl reject it with: "Unrecognized character found in mode field".

tests/misc/csplit-io-err.sh

@@ -66,9 +66,9 @@ gcc_shared_ k.c k.so \
 # Split the input, and force fwrite() failure -
 # the 'csplit' command should fail with exit code 1
 # (checked with 'returns_ 1 ... || fail=1')
-seq 10 \
-  | LD_PRELOAD=$LD_PRELOAD:./k.so returns_ 1 csplit - 1 4 2>out \
-  || fail=1
+seq 10 |
+(export LD_PRELOAD=$LD_PRELOAD:./k.so
+ returns_ 1 csplit - 1 4 2>out) || fail=1
 
 test -e preloaded || skip_ 'LD_PRELOAD interception failed'
 

tests/misc/nohup.sh

@@ -118,6 +118,8 @@ EOF
 # Make sure it fails with exit status of 125 when given too few arguments,
 # except that POSIX requires 127 in this case.
 returns_ 125 nohup >/dev/null 2>&1 || fail=1
-POSIXLY_CORRECT=1 returns_ 127 nohup >/dev/null 2>&1 || fail=1
+export POSIXLY_CORRECT=1
+returns_ 127 nohup >/dev/null 2>&1 || fail=1
+unset POSIXLY_CORRECT
 
 Exit $fail

tests/misc/printenv.sh

@@ -59,8 +59,10 @@ EOF
 compare exp out || fail=1
 
 # Exit status reflects missing variable, but remaining arguments processed.
-ENV_TEST1=a returns_ 1 env -- printenv ENV_TEST2 ENV_TEST1 > out || fail=1
-ENV_TEST1=a returns_ 1 env -- printenv ENV_TEST1 ENV_TEST2 >> out || fail=1
+export ENV_TEST1=a
+returns_ 1 env -- printenv ENV_TEST2 ENV_TEST1 > out || fail=1
+returns_ 1 env -- printenv ENV_TEST1 ENV_TEST2 >> out || fail=1
+unset ENV_TEST1
 cat <<EOF > exp || framework_failure_
 a
 a

tests/rm/rm-readdir-fail.sh

@@ -88,7 +88,8 @@ gcc_shared_ k.c k.so \
 export READDIR_PARTIAL
 for READDIR_PARTIAL in '' '1'; do
   rm -f preloaded
-  (LD_PRELOAD=$LD_PRELOAD:./k.so returns_ 1 rm -Rf dir 2>>err) || fail=1
+  (export LD_PRELOAD=$LD_PRELOAD:./k.so
+   returns_ 1 rm -Rf dir 2>>err) || fail=1
   test -f preloaded ||
     skip_ "internal test failure: maybe LD_PRELOAD doesn't work?"
 done