Fix command substitutions in here-docs (rhbz#994241, rhbz#1036802)

When ksh was compiled with SHOPT_SPAWN (the default), any command
substitution embedded in a here-document returned an empty string.
The bug was also present in 93u+ 2012-08-01 (although not in every
case as some systems compile it without SHOPT_SPAWN).

This fixes it by applying a slightly edited combination of two Red
Hat patches (the second containing a fix for the first), which
backport a new command substitution mechanism from the abandoned
ksh 93v- beta version. The originals are:

642af4d6/f/ksh-20120801-macro.patch
642af4d6/f/ksh-20120801-fd2lost.patch

src/cmd/ksh93/include/io.h:
- The iopipe() function from xec.c is now needed in sh_subshell()
  (subshell.c), so rename it to sh_iounpipe() and declare it as an
  extern here. The 93v- beta did it as well. (The Red Hat patch did
  this without renaming it.)

src/cmd/ksh93/sh/xec.c:
- Backport new versions of iousepipe() and sh_iounpipe() from ksh
  93v-. New 'type' flaggery is introduced to distinguish between
  different command substitution conditions. What all that means
  remains to be determined.
- sh_exec(): I made one change to the Red Hat patch myself: if in a
  subshell and the type flags FAMP (for "ampersand" as in '&' as in
  background job) and TFORK are set, continue to call sh_subfork()
  to fork the subshell unconditionally, instead of only if we're in
  a command substitution connected to an unseekable file. Maybe the
  latter works for the 93v- code, but on 93u+(m) it causes a couple
  of regressions, which are fixed by my change:
  signal.sh[273]: subshell ignoring signal does not send signal to parent
  signal.sh[276]: subshell catching signal does not send signal to parent
  Details: https://github.com/ksh93/ksh/issues/104#issuecomment-696341902

src/cmd/ksh93/sh/macro.c,
src/cmd/ksh93/sh/subshell.c:
- Updates that go with those new functions.

Fixes:   https://github.com/ksh93/ksh/issues/104
Affects: https://github.com/ksh93/ksh/issues/124

src/cmd/ksh93/tests/signal.sh

@@ -272,10 +272,22 @@ done < tst.got
 
 if	[[ ${SIG[USR1]} ]]
 then	float s=$SECONDS
-	[[ $(LC_ALL=C $SHELL -c 'trap "print SIGUSR1 ; exit 0" USR1; (trap "" USR1 ; exec kill -USR1 $$ & sleep .5); print done') == SIGUSR1 ]] || err_exit 'subshell ignoring signal does not send signal to parent'
+	exp=SIGUSR1
+	got=$(LC_ALL=C $SHELL -c '
+		trap "print SIGUSR1 ; exit 0" USR1
+		(trap "" USR1 ; exec kill -USR1 $$ & sleep .5)
+		print done')
+	[[ $got == "$exp" ]] || err_exit 'subshell ignoring signal does not send signal to parent' \
+		"(expected '$exp', got '$got')"
 	(( (SECONDS-s) < .4 )) && err_exit 'parent does not wait for child to complete before handling signal'
 	((s = SECONDS))
-	[[ $(LC_ALL=C $SHELL -c 'trap "print SIGUSR1 ; exit 0" USR1; (trap "exit" USR1 ; exec kill -USR1 $$ & sleep .5); print done') == SIGUSR1 ]] || err_exit 'subshell catching signal does not send signal to parent'
+	exp=SIGUSR1
+	got=$(LC_ALL=C $SHELL -c '
+		trap "print SIGUSR1 ; exit 0" USR1
+		(trap "exit" USR1 ; exec kill -USR1 $$ & sleep .5)
+		print done')
+	[[ $got == "$exp" ]] || err_exit 'subshell catching signal does not send signal to parent' \
+		"(expected '$exp', got '$got')"
 	(( SECONDS-s < .4 )) && err_exit 'parent completes early'
 fi
 

src/cmd/ksh93/tests/subshell.sh

@@ -759,5 +759,40 @@ SHELL=$SHELL "$SHELL" -c '
 ' | awk '/^DEBUG/ { pid[NR] = $2; }  END { exit !(pid[1] == pid[2] && pid[2] == pid[3]); }' \
 || err_exit "setting PATH to readonly in subshell triggers an erroneous fork"
 
+# ======'
+# Test command substitution with external command in here-document
+# https://github.com/ksh93/ksh/issues/104
+expect=$'/dev/null\n/dev/null'
+actual=$(
+	cat <<-EOF
+		$(ls /dev/null)
+		`ls /dev/null`
+	EOF
+)
+[[ $actual == "$expect" ]] || err_exit 'Command substitution in here-document fails' \
+	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+
+# ...and in pipeline (rhbz#994251)
+expect=/dev/null
+actual=$(cat /dev/null | "$binecho" `ls /dev/null`)
+[[ $actual == "$expect" ]] || err_exit 'Command substitution in pipeline fails (1)' \
+	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+
+# ...and in pipeline again (rhbz#1036802: standard error was misdirected)
+expect=$'END2\naaa\nEND1\nEND3'
+actual=$(export bincat binecho; "$SHELL" 2>&1 -c \
+	'function foo
+	{
+		"$binecho" hello >/dev/null 2>&1
+		"$binecho" aaa | "$bincat"
+		echo END1
+		echo END2 >&2
+	}
+	echo "$(foo)" >&2
+	echo END3 >&2
+	exit')
+[[ $actual == "$expect" ]] || err_exit 'Command substitution in pipeline fails (2)' \
+	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
+
 # ======
 exit $((Errors<125?Errors:125))