test/[: Fix binary -a/-o operators in POSIX mode

POSIX requires
	test "$a" -a "$b"
to return true if both $a and $b are non-empty, and
	test "$a" -o "$b"
to return true if either $a or $b is non-empty.

In ksh, this fails if "$a" is '!' or '(' as this causes ksh to
interpret the -a and -o as unary operators (-a being a file
existence test like -e, and -o being a shell option test).

$ test ! -a ""; echo "$?"
0		(expected: 1/false)
$ set -o trackall; test ! -o trackall; echo "$?"
1		(expected: 0/true)
$ test \( -a \); echo "$?"
ksh: test: argument expected
2		(expected: 0/true)
$ test \( -o \)
ksh: test: argument expected
2		(expected: 0/true)

Unfortunately this problem cannot be fixed without risking breakage
in legacy scripts. For instance, a script may well use
	test ! -a filename
to check that a filename is nonexistent. POSIX specifies that this
always return true as it is a test for the non-emptiness of both
strings '!' and 'filename'.

So this commit fixes it for POSIX mode only.

src/cmd/ksh93/bltins/test.c: e3():
- If the posix option is active, specially handle the case of
  having at least three arguments with the second being -a or -o,
  overriding their handling as unary operators.

src/cmd/ksh93/data/testops.c:
- Update 'test --man --' date and say that unary -a is deprecated.

src/cmd/ksh93/sh.1:
- Document the fix under the -o posix option.
- For test/[, explain that binary -a/-o are deprecated.

src/cmd/ksh93/tests/bracket.sh:
- Add tests based on reproducers in bug report.

Resolves: https://github.com/ksh93/ksh/issues/330

NEWS

@@ -3,6 +3,14 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-11-13:
+
+- The test/[ built-in command is fixed so that the binary -a (and) and -o (or)
+  operators, as in [ "$a" -a "$b" ] or [ "$a" -o "$b" ], work even if "$a" is
+  '!' or '('. To avoid breaking backwards compatibility with the nonstandard
+  unary [ -a "$file" ] and [ -o "$option" ] operators in combination with '!'
+  or parentheses, this fix is only activated if the posix option is on.
+
 2021-11-07:
 
 - Fixed a bug that could corrupt output if standard output is closed upon

src/cmd/ksh93/bltins/test.c

@@ -243,8 +243,9 @@ done:
 /*
  * evaluate a test expression.
  * flag is 0 on outer level
- * flag is 1 when in parenthesis
- * flag is 2 when evaluating -a 
+ * flag is 1 when in parentheses
+ * flag is 2 when evaluating -a (TEST_AND)
+ * flag is 3 when evaluating -o (TEST_OR)
  */
 static int expr(struct test *tp,register int flag)
 {
@@ -308,6 +309,17 @@ static int e3(struct test *tp)
 	register int op;
 	char *binop;
 	arg=nxtarg(tp,0);
+	if(sh_isoption(SH_POSIX) && tp->ap + 1 < tp->ac && ((op=sh_lookup(tp->av[tp->ap],shtab_testops)) & TEST_BINOP))
+	{	/*
+		 * In POSIX mode, makes sure standard binary -a/-o takes precedence
+		 * over nonstandard unary -a/-o if the lefthand expression is "!" or "("
+		 */
+		tp->ap++;
+		if(op==TEST_AND)
+			return(*arg && expr(tp,2));
+		else /* TEST_OR */
+			return(*arg || expr(tp,3));
+	}
 	if(arg && c_eq(arg, '!'))
 		return(!e3(tp));
 	if(c_eq(arg, '('))

src/cmd/ksh93/data/testops.c

@@ -57,7 +57,7 @@ const Shtable_t shtab_testops[] =
 };
 
 const char sh_opttest[] =
-"[-1c?\n@(#)$Id: test (ksh 93u+m) 2020-08-31 $\n]"
+"[-1c?\n@(#)$Id: test (ksh 93u+m) 2021-11-13 $\n]"
 "[--catalog?" SH_DICT "]"
 "[+NAME?test, [ - evaluate expression]"
 "[+DESCRIPTION?\btest\b evaluates expressions and returns its result using the "
@@ -97,7 +97,7 @@ const char sh_opttest[] =
 	"[+?Operators marked with a * are not part of the POSIX standard.]"
 "}"
 "[+UNARY OPERATORS?These evaluate as True if:]{"
-	"[+-a \afile\a *?Same as \b-e\b.]"
+	"[+-a \afile\a *?Deprecated. Same as \b-e\b.]"
 	"[+-b \afile\a?\afile\a is a block special file.]"
 	"[+-c \afile\a?\afile\a is a character special file.]"
 	"[+-d \afile\a?\afile\a is a directory.]"

src/cmd/ksh93/include/version.h

@@ -21,7 +21,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-beta.2"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2021-11-07"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2021-11-13"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2021 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/sh.1

@@ -7244,6 +7244,12 @@ disables the \fB&>\fR redirection shorthand;
 .IP \[bu]
 makes the \fB<>\fR redirection operator default to redirecting standard input
 if no file descriptor number precedes it;
+.IP \[bu]
+changes the \fBtest\fR/\fB[\fR built-in command to make its deprecated
+\fIexpr1\fR \fB-a\fR \fIexpr2\fR and \fIexpr1\fR \fB-o\fR \fIexpr2\fR operators
+work even if \fIexpr1\fR equals "\fB!\fR" or "\fb(\fR" (which means the
+nonstandard unary \fB-a\fR \fIfile\fR and \fB-o\fR \fIoption\fR operators
+cannot be directly negated using \fB!\fR or wrapped in parentheses);
 and
 .IP \[bu]
 disables a hack that makes \fBtest -t\fR (\fB[ -t ]\fR) equivalent to
@@ -7451,13 +7457,15 @@ to those specified for the \f3[[\fP compound command under
 above, but with several important differences. The \f3=\fP, \f3==\fP and
 \f3!=\fP operators test for string (in)equality without pattern matching;
 the \f3==\fP variant is nonstandard and should not be used. The \f3=\(ap\fP,
-\f3<\fP, \f3>\fP, \f3&&\fP and \f3||\fP operators are not available. Most
+\f3<\fP, \f3>\fP, \f3&&\fP and \f3||\fP operators are not available. Instead
+of \f3&&\fP and \f3||\fP, the \f3-a\fP and \f3-o\fP binary operators can be
+used, but they are fraught with pitfalls due to grammatical ambiguities and
+therefore deprecated in favor of invoking separate \f3test\fP commands. Most
 importantly, as \f3test\fP and \f3[\fP are simple regular commands, field
 splitting and file name generation \f2are\fP performed on all their
 arguments and all aspects of regular shell grammar (such as redirection)
 remain active. This is usually harmful, so care must be taken to quote
-arguments and expansions to avoid this. There are also certain inherent
-grammatical ambiguities in the expressions. To avoid the many pitfalls
+arguments and expansions to avoid this. To avoid the many pitfalls
 arising from these issues, the \f3[[\fP compound command should be used
 instead. The primary purpose of the \f3test\fP and \f3[\fP commands is
 compatibility with other shells that lack \f3[[\fP.

src/cmd/ksh93/tests/bracket.sh

@@ -423,5 +423,16 @@ foo=10
 && [ ! ! -n x -a ! ! ! ! -n x -a ! ! ! ! ! ! -n x ] \
 || err_exit '! does not negate ! in [ ... ]'
 
+# ======
+# https://github.com/ksh93/ksh/issues/330
+if	(set -o posix) 2>/dev/null
+then	set -o posix -o trackall
+	test ! -a "" && err_exit "POSIX test/[: binary -a operator does not work with '!' as left-hand expression"
+	test \( -a \) 2>/dev/null || err_exit "POSIX test/[: binary -a operator does not work with '(' as left-hand expression"
+	test ! -o trackall || err_exit "POSIX test/[: binary -o operator does not work with '!' as left-hand expression"
+	test \( -o \) 2>/dev/null || err_exit "POSIX test/[: binary -o operator does not work with '(' as left-hand expression"
+	set +o posix
+fi
+
 # ======
 exit $((Errors<125?Errors:125))