build system: fix detection of default system directories

src/cmd/INIT/iffe.sh:
- Fix "standard system directories" for the cmd test, which were
  hardcoded as bin, /etc, /usr/bin, /usr/etc, /usr/ucb. That's both
  unportable and antiquated. Replace this with the path output by
  'getconf PATH'.
- Add fixes from modernish for 'getconf PATH' output to compensate
  for bugs/shortcomigns in NixOS and AIX. Source:
  9e4bf5eb/lib/modernish/aux/defpath.sh
  Ref.: https://github.com/NixOS/nixpkgs/issues/65512

src/lib/libast/comp/conf.tab: PATH:
- Add the NixOS and AIX default path fixes here too; this fixes
  'command -p' and the builtin 'getconf PATH' on these systems.

bin/package, src/cmd/INIT/package.sh:
- Re-support being launched with just the command name 'package' in
  the command line (if the 'package' command is in $PATH). At least
  one other script in the build system does this. (re: 6cc2f6a0)
- Go back three levels (../../..) if we were invoked from
  arch/*/bin/package, otherwise we won't find src/cmd/ksh93/SHOPT.sh.

bin/package

@@ -43,11 +43,31 @@ case $0 in
 	*)	echo "this script must live in bin/" >&2
 		exit 1 ;;
 	esac
-	cd .. || exit
+	case $mydir in
+	*/arch/*/*/bin)
+		cd .. ;;
+	*/arch/*/bin)
+		cd ../../.. ;;
+	*)	cd .. ;;
+	esac || exit
 	unset mydir ;;
 package)
-	echo "this script must be invoked with a direct path, e.g. bin/package" >&2
+	me=`command -v package` || me=`which package` || exit
-	exit 1 ;;
+	mydir=`echo "$me" | sed 's,/package$,,'`
+	cd "$mydir" || exit
+	case $PWD in
+	*/bin)	;;
+	*)	echo "this script must live in bin/" >&2
+		exit 1 ;;
+	esac
+	case $mydir in
+	*/arch/*/*/bin)
+		cd .. ;;
+	*/arch/*/bin)
+		cd ../../.. ;;
+	*)	cd .. ;;
+	esac || exit
+	unset me mydir ;;
 *)
 	echo "this script must be named 'package'" >&2
 	exit 1 ;;

src/cmd/INIT/iffe.sh

@@ -31,7 +31,7 @@ AIX)	unset LIBPATH ;;
 esac
 
 command=iffe
-version=2012-07-17 # update in USAGE too #
+version=2021-02-03 # update in USAGE too #
 
 compile() # $cc ...
 {
@@ -95,11 +95,45 @@ is_hdr() # [ - ] [ file.c ] hdr
 pkg() # package
 {
 	case $1 in
-	'')	pth=`getconf PATH 2>/dev/null`
+	'')	# Determine default system path, store in $pth.
+		pth=`
+			PATH=/run/current-system/sw/bin:/usr/xpg7/bin:/usr/xpg6/bin:/usr/xpg4/bin:/bin:/usr/bin:$PATH
+			exec getconf PATH 2>/dev/null
+		`
 		case $pth in
-		'')	pth="/bin /usr/bin" ;;
+		'' | [!/]* | *:[!/]* | *: )
+			pth="/bin /usr/bin /sbin /usr/sbin" ;;
 		*:*)	pth=`echo "$pth" | sed 's/:/ /g'` ;;
 		esac
+		# Fix for NixOS. Not all POSIX standard utilities come with the default system,
+		# e.g. 'bc', 'file', 'vi'. The command that NixOS recommends to get missing
+		# utilities, e.g. 'nix-env -iA nixos.bc', installs them in a default profile
+		# directory that is not in $(getconf PATH). So add this path to the standard path.
+		# See: https://github.com/NixOS/nixpkgs/issues/65512
+		if	test -e /etc/NIXOS &&
+			nix_profile_dir=/nix/var/nix/profiles/default/bin &&
+			test -d "$nix_profile_dir"
+		then	case " $pth " in
+			*" $nix_profile_dir "* )
+				# nothing to do
+				;;
+			* )	# insert the default profile directory as the second entry
+				pth=`
+					set $pth
+					one=$1
+					shift
+					echo "$one $nix_profile_dir${1+ }$@"
+				` ;;
+			esac
+		fi
+		# Fix for AIX. At least as of version 7.1, the system default 'find', 'diff -u' and 'patch' utilities
+		# are broken and/or non-compliant in ways that make them incompatible with POSIX 2018. However, GNU
+		# utilities are commonly installed in /opt/freeware/bin, and under standard names (no g- prefix).
+		if	test -d /opt/freeware/bin
+		then	case `uname` in
+			AIX )	pth="/opt/freeware/bin $pth" ;;
+			esac
+		fi
 		return
 		;;
 	'<')	shift
@@ -719,11 +753,12 @@ set=
 case `(getopts '[-][123:xyz]' opt --xyz; echo 0$opt) 2>/dev/null` in
 0123)	USAGE=$'
 [-?
-@(#)$Id: iffe (AT&T Research) 2012-07-17 $
+@(#)$Id: iffe (ksh 93u+m) 2021-02-03 $
 ]
 [-author?Glenn Fowler <gsf@research.att.com>]
 [-author?Phong Vo <kpv@research.att.com>]
-[-copyright?Copyright (c) 1994-2012 AT&T Intellectual Property]
+[-copyright?(c) 1994-2012 AT&T Intellectual Property]
+[-copyright?(c) 2020-2021 Contributors to https://github.com/ksh93/ksh]
 [-license?http://www.eclipse.org/org/documents/epl-v10.html]
 [+NAME?iffe - C compilation environment feature probe]
 [+DESCRIPTION?\biffe\b is a command interpreter that probes the C
@@ -915,8 +950,8 @@ case `(getopts '[-][123:xyz]' opt --xyz; echo 0$opt) 2>/dev/null` in
 	[+ver \aname\a \aYYYYMMDD\a?\b#define\b \aNAME\a_VERSION \aYYYYMMDD\a
 		(\aNAME\a is \aname\a converted to upper case).]
 	[+cmd \aname\a?Defines \b_cmd_\b\aname\a if \aname\a is an executable
-		in one of the standard system directories (\b/bin, /etc,
+		in one of the standard system directories
-		/usr/bin, /usr/etc, /usr/ucb\b).
+		(as output by \bgetconf PATH\b).
 		\b_\b\adirectory\a\b_\b\aname\a is defined for \adirectory\a
 		in which \aname\a is found (with \b/\b translated to \b_\b).]
 	[+dat \aname\a?Defines \b_dat_\b\aname\a if \aname\a is a data symbol
@@ -3617,34 +3652,30 @@ int main(){printf("hello");return(0);}
 					esac
 					is $o $a
 					k=1
-					for j in "" usr
+					pkg $pth  # set system default path
-					do	case $j in
+					for d in $pth
-						"")	d= s= ;;
+					do	if	test -f "$d/$a"
-						*)	d=/$j s=_$j ;;
+						then	s=`echo "$d" | LC_ALL=C sed 's,[^0-9A-Za-z],_,g'`
-						esac
+							case $k in
-						for i in bin etc ucb
+							1)	k=0
-						do	if	test -f $d/$i/$a
+								case $M in
-							then	case $k in
+								*-*)	;;
-								1)	k=0
+								*)	usr="$usr$nl#define $m 1"
-									case $M in
+									case $define in
-									*-*)	;;
+									1)	echo "#define $m	1	/* $a in $pth */" ;;
-									*)	usr="$usr$nl#define $m 1"
+									n)	echo "$m=1" ;;
-										case $define in
-										1)	echo "#define $m	1	/* $a in ?(/usr)/(bin|etc|ucb) */" ;;
-										n)	echo "$m=1" ;;
-										esac
-										;;
 									esac
 									;;
 								esac
-								c=${s}_${i}_${v}
+								;;
-								usr="$usr$nl#define $c 1"
+							esac
-								case $define in
+							c=${s}_${v}
-								1)	echo "#define $c	1	/* $d/$i/$a found */" ;;
+							usr="$usr$nl#define $c 1"
-								n)	echo "$c=1" ;;
+							case $define in
-								esac
+							1)	echo "#define $c	1	/* $d/$a found */" ;;
-							fi
+							n)	echo "$c=1" ;;
-						done
+							esac
+						fi
 					done
 					case $k in
 					0)	success ;;

src/cmd/INIT/package.sh

@@ -43,11 +43,31 @@ case $0 in
 	*)	echo "this script must live in bin/" >&2
 		exit 1 ;;
 	esac
-	cd .. || exit
+	case $mydir in
+	*/arch/*/*/bin)
+		cd .. ;;
+	*/arch/*/bin)
+		cd ../../.. ;;
+	*)	cd .. ;;
+	esac || exit
 	unset mydir ;;
 package)
-	echo "this script must be invoked with a direct path, e.g. bin/package" >&2
+	me=`command -v package` || me=`which package` || exit
-	exit 1 ;;
+	mydir=`echo "$me" | sed 's,/package$,,'`
+	cd "$mydir" || exit
+	case $PWD in
+	*/bin)	;;
+	*)	echo "this script must live in bin/" >&2
+		exit 1 ;;
+	esac
+	case $mydir in
+	*/arch/*/*/bin)
+		cd .. ;;
+	*/arch/*/bin)
+		cd ../../.. ;;
+	*)	cd .. ;;
+	esac || exit
+	unset me mydir ;;
 *)
 	echo "this script must be named 'package'" >&2
 	exit 1 ;;

src/lib/libast/comp/conf.tab

@@ -375,9 +375,41 @@ PATH				AST	CS 1 MU		sh{
 	*)	CONF_path=`"$CONF_getconf" PATH` ;;
 	esac
 	case $CONF_path in
-	'')	echo '"/bin:/usr/bin:/sbin:/usr/sbin"' ;;
+	'' | [!/]* | *:[!/]* | *: )
-	*)	echo "\\"$CONF_path\\"" ;;
+		CONF_path=/bin:/usr/bin:/sbin:/usr/sbin ;;
 	esac
+	# Fix for NixOS. Not all POSIX standard utilities come with the default system,
+	# e.g. 'bc', 'file', 'vi'. The command that NixOS recommends to get missing
+	# utilities, e.g. 'nix-env -iA nixos.bc', installs them in a default profile
+	# directory that is not in $(getconf PATH). So add this path to the standard path.
+	# See: https://github.com/NixOS/nixpkgs/issues/65512
+	if	test -e /etc/NIXOS &&
+		nix_profile_dir=/nix/var/nix/profiles/default/bin &&
+		test -d "$nix_profile_dir"
+	then	case ":$CONF_path:" in
+		*:"$nix_profile_dir":* )
+			# nothing to do
+			;;
+		* )	# insert the default profile directory as the second entry
+			CONF_path=`
+				set -f
+				IFS=:
+				set $CONF_path
+				one=$1
+				shift
+				echo "$one:$nix_profile_dir${1+:}$*"
+			` ;;
+		esac
+	fi
+	# Fix for AIX. At least as of version 7.1, the system default 'find', 'diff -u' and 'patch' utilities
+	# are broken and/or non-compliant in ways that make them incompatible with POSIX 2018. However, GNU
+	# utilities are commonly installed in /opt/freeware/bin, and under standard names (no g- prefix).
+	if	test -d /opt/freeware/bin
+	then	case `uname` in
+		AIX )	CONF_path="/opt/freeware/bin:$CONF_path" ;;
+		esac
+	fi
+	echo "\\"$CONF_path\\""
 }
 PATH_MAX			POSIX	PC 1 CDLMUX	MAXPATHLEN 1024
 PBS				POSIX	SC 2 FUW