Revert "[1.0 release prep] Remove tilde expansion discipline"

This reverts c0334e32, thereby restoring 936a1939.

After the fixes in 0a343244 and a2bc49be, the tilde expansion
disciplines work nicely, so they can come back to the 1.0 branch.

src/cmd/ksh93/tests/pty.sh

@@ -751,6 +751,24 @@ r ^:test-2: echo Success\r\n$
 r ^Success\r\n$
 !
 
+# err_exit #
+((SHOPT_VSH || SHOPT_ESH)) && tst $LINENO <<"!"
+L value of $? after tilde expansion in tab completion
+
+# Make sure that a .sh.tilde.set discipline function
+# cannot influence the exit status.
+
+w .sh.tilde.set() { true; }
+w HOME=/tmp
+w false ~\t
+u false /tmp
+w echo "Exit status is: $?"
+u Exit status is: 1
+w (exit 42)
+w echo $? ~\t
+u 42 /tmp
+!
+
 # err_exit #
 ((SHOPT_MULTIBYTE && (SHOPT_VSH || SHOPT_ESH))) &&
 [[ ${LC_ALL:-${LC_CTYPE:-${LANG:-}}} =~ [Uu][Tt][Ff]-?8 ]] &&

src/cmd/ksh93/tests/tilde.sh

@@ -107,6 +107,8 @@ got=~
 HOME=$saveHOME
 
 # ======
+# Tilde expansion discipline function tests
+
 # This nonfunctional mess was removed in ksh 93u+m ...
 if builtin .sh.tilde 2>/dev/null
 then	got=$(.sh.tilde & wait "$!" 2>&1)
@@ -114,5 +116,57 @@ then	got=$(.sh.tilde & wait "$!" 2>&1)
 		"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$got"))"
 fi
 
+# ... and replaced by a proper use of discipline functions that allows customising tilde expansion.
+((.sh.version >= 20210316)) &&
+for disc in get set
+do	(
+		ulimit -t unlimited 2>/dev/null  # fork subshell to cope with a possible crash
+
+		eval ".sh.tilde.$disc()
+		{
+			case \${.sh.${ [[ $disc == get ]] && print tilde || print value; }} in
+			'~tmp')	.sh.value=\$tmp ;;
+			'~INC')	.sh.value=\$((++i)) ;;
+			'~spc') .sh.value=$'one\ttwo  three\n\tfour' ;;
+			'~')	.sh.value=~/addition ;;  # this should not recurse
+			esac
+		}"
+
+		got=~/foo
+		exp=$HOME/addition/foo
+		[[ $got == "$exp" ]] || err_exit "$disc discipline: bare tilde expansion:" \
+			"expected $(printf %q "$exp"), got $(printf %q "$got")"
+
+		.sh.tilde=oldvalue
+		got=$(print ~tmp/foo.$$; print "${.sh.tilde}")
+		exp=$tmp/foo.$$$'\n'$tmp
+		[[ $got == "$exp" ]] || err_exit "$disc discipline: result left in \${.sh.tilde}:" \
+			"expected $(printf %q "$tmp"), got $(printf %q "${.sh.tilde}")"
+		[[ ${.sh.tilde} == oldvalue ]] || err_exit "$disc discipline: \${.sh.tilde} subshell leak"
+
+		i=0
+		set -- ~INC ~INC ~INC ~INC ~INC
+		got=$#,$1,$2,$3,$4,$5
+		exp=5,1,2,3,4,5
+		[[ $got == "$exp" ]] || err_exit "$disc discipline: counter:" \
+			"expected $(printf %q "$exp"), got $(printf %q "$got")"
+		((i==5)) || err_exit "$disc discipline: counter: $i != 5"
+
+		set -- ~spc ~spc ~spc
+		got=$#,$1,$2,$3
+		exp=$'3,one\ttwo  three\n\tfour,one\ttwo  three\n\tfour,one\ttwo  three\n\tfour'
+		[[ $got == "$exp" ]] || err_exit "$disc discipline: quoting of whitespace:" \
+			"expected $(printf %q "$exp"), got $(printf %q "$got")"
+
+		print "$Errors" >$tmp/Errors
+	) &
+	wait "$!" 2>crashmsg
+	if	((!(e = $?)))
+	then	read Errors <$tmp/Errors
+	else	err_exit ".sh.tilde.$disc discipline function crashes the shell" \
+			"(got status $e$( ((e>128)) && print -n / && kill -l "$e"), $(printf %q "$(<crashmsg)"))"
+	fi
+done
+
 # ======
 exit $((Errors<125?Errors:125))

src/cmd/ksh93/tests/variables.sh

@@ -1029,6 +1029,7 @@ set -- \
 	".sh.math" \
 	".sh.pool" \
 	".sh.pid" \
+	".sh.tilde" \
 	"SHLVL" \
 	"CSWIDTH"