From 523b7c70177a2d42b3bca7ca5ebd6a0ec3fbbd8d Mon Sep 17 00:00:00 2001
From: Martijn Dekker <martijn@inlv.org>
Date: Sun, 24 Jul 2022 06:09:59 +0200
Subject: [PATCH] Part revert 39e467da

Even tough sh_subtmpfile() should only be relevant to command
substitutions, checking the sh.comsub flag instead of sh.subshell
before calling is not valid in all cases; subshells of command
substitutions run into problems in some oddly specific cases, e.g.,
both 'eval' and an external command must be involved. The ksh
regression tests didn't detect a problem, but both modernish[*] and
shellspec[*] have one regression test failure after that change.

Minimal reproducer, assuming a cat at /bin/cat:

    v=$(eval 'print output | /bin/cat')
    print -r "v=[$v]"

Actual output:

    output
    v=[]

Expected output:

    v=[output]
---
 src/cmd/ksh93/sh/args.c         | 2 +-
 src/cmd/ksh93/sh/io.c           | 4 ++--
 src/cmd/ksh93/sh/xec.c          | 6 +++---
 src/cmd/ksh93/tests/subshell.sh | 7 +++++++
 4 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/cmd/ksh93/sh/args.c b/src/cmd/ksh93/sh/args.c
index faee9c45d..18c76efe6 100644
--- a/src/cmd/ksh93/sh/args.c
+++ b/src/cmd/ksh93/sh/args.c
@@ -721,7 +721,7 @@ struct argnod *sh_argprocsub(struct argnod *argp)
 	ap->argflag |= ARG_MAKE;
 	ap->argflag &= ~ARG_RAW;
 	fd = argp->argflag&ARG_RAW;
-	if(fd==0 && sh.comsub)
+	if(fd==0 && sh.subshell)
 		sh_subtmpfile();
 #if SHOPT_DEVFD
 	sfwrite(sh.stk,e_devfdNN,8);
diff --git a/src/cmd/ksh93/sh/io.c b/src/cmd/ksh93/sh/io.c
index 10001806d..5bc48e9dc 100644
--- a/src/cmd/ksh93/sh/io.c
+++ b/src/cmd/ksh93/sh/io.c
@@ -1173,7 +1173,7 @@ int	sh_redirect(struct ionod *iop, int flag)
 			memset(ap, 0, ARGVAL);
 			if(iof&IOPUT)
 				ap->argflag = ARG_RAW;
-			else if(sh.comsub)
+			else if(sh.subshell)
 				sh_subtmpfile();
 			ap->argchn.ap = (struct argnod*)fname;
 			ap = sh_argprocsub(ap);
@@ -1241,7 +1241,7 @@ int	sh_redirect(struct ionod *iop, int flag)
 					}
 					if(sh.subshell && dupfd==1)
 					{
-						if(sh.comsub)
+						if(sh.subshell)
 							sh_subtmpfile();
 						dupfd = sffileno(sfstdout);
 					}
diff --git a/src/cmd/ksh93/sh/xec.c b/src/cmd/ksh93/sh/xec.c
index 70e0dba7d..9fed172a0 100644
--- a/src/cmd/ksh93/sh/xec.c
+++ b/src/cmd/ksh93/sh/xec.c
@@ -1245,7 +1245,7 @@ int sh_exec(register const Shnode_t *t, int flags)
 						bp->sigset = 0;
 						bp->notify = 0;
 						bp->flags = (OPTIMIZE!=0);
-						if(sh.comsub && nv_isattr(np,BLT_NOSFIO))
+						if(sh.subshell && nv_isattr(np,BLT_NOSFIO))
 							sh_subtmpfile();
 						if(argn)
 							sh.exitval = (*sh.bltinfun)(argn,com,(void*)bp);
@@ -1445,7 +1445,7 @@ int sh_exec(register const Shnode_t *t, int flags)
 			register pid_t parent;
 			int no_fork,jobid;
 			int pipes[3];
-			if(sh.comsub)
+			if(sh.subshell)
 				sh_subtmpfile();
 			if(no_fork = check_exec_optimization(type,execflg,execflg2,t->fork.forkio))
 				job.parent=parent=0;
@@ -1823,7 +1823,7 @@ int sh_exec(register const Shnode_t *t, int flags)
 			echeck = 1;
 			job.exitval = 0;
 			job.curjobid = 0;
-			if(sh.comsub)
+			if(sh.subshell)
 				sh_subtmpfile();
 			sh.inpipe = pvo;
 			sh.outpipe = pvn;
diff --git a/src/cmd/ksh93/tests/subshell.sh b/src/cmd/ksh93/tests/subshell.sh
index 1a8da97cc..402d083b2 100755
--- a/src/cmd/ksh93/tests/subshell.sh
+++ b/src/cmd/ksh93/tests/subshell.sh
@@ -1178,5 +1178,12 @@ exp=OK
 [[ $got == "$exp" ]] || err_exit 'trap ignored when signalled from a subshell that is the last command' \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
+# ======
+# if this fails with empty output, sh_subtmpfile() is not getting called where it should be
+exp='some output'
+{ got=$(eval 'print -r -- "$exp" | "$bincat"'); } >/dev/null
+[[ $got == "$exp" ]] || err_exit 'command substitution did not catch output' \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))