awk: fix precedence of = relative to ==

Discovered while adding code to disallow assignments to non-lvalues

function                                             old     new   delta
parse_expr                                           936     991     +55
.rodata                                           105243  105247      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 59/0)               Total: 59 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 50 insertions, 21 deletions

diff --git a/editors/awk.c b/editors/awk.c
index c49ad6e..0f062dc 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -337,7 +337,9 @@ static void debug_parse_print_tc(uint32_t n)
 #undef P
 #undef PRIMASK
 #undef PRIMASK2
-#define P(x)      (x << 24)
+/* Smaller 'x' means _higher_ operator precedence */
+#define PRECEDENCE(x) (x << 24)
+#define P(x)      PRECEDENCE(x)
 #define PRIMASK   0x7F000000
 #define PRIMASK2  0x7E000000
 
@@ -360,7 +362,7 @@ enum {
 	OC_MOVE = 0x1f00,       OC_PGETLINE = 0x2000,   OC_REGEXP = 0x2100,
 	OC_REPLACE = 0x2200,    OC_RETURN = 0x2300,     OC_SPRINTF = 0x2400,
 	OC_TERNARY = 0x2500,    OC_UNARY = 0x2600,      OC_VAR = 0x2700,
-	OC_DONE = 0x2800,
+	OC_CONST = 0x2800,      OC_DONE = 0x2900,
 
 	ST_IF = 0x3000,         ST_DO = 0x3100,         ST_FOR = 0x3200,
 	ST_WHILE = 0x3300
@@ -440,9 +442,9 @@ static const uint32_t tokeninfo[] ALIGN4 = {
 #define TI_PREINC (OC_UNARY|xV|P(9)|'P')
 #define TI_PREDEC (OC_UNARY|xV|P(9)|'M')
 	TI_PREINC,               TI_PREDEC,               OC_FIELD|xV|P(5),
-	OC_COMPARE|VV|P(39)|5,   OC_MOVE|VV|P(74),        OC_REPLACE|NV|P(74)|'+', OC_REPLACE|NV|P(74)|'-',
-	OC_REPLACE|NV|P(74)|'*', OC_REPLACE|NV|P(74)|'/', OC_REPLACE|NV|P(74)|'%', OC_REPLACE|NV|P(74)|'&',
-	OC_BINARY|NV|P(29)|'+',  OC_BINARY|NV|P(29)|'-',  OC_REPLACE|NV|P(74)|'&', OC_BINARY|NV|P(15)|'&',
+	OC_COMPARE|VV|P(39)|5,   OC_MOVE|VV|P(38),        OC_REPLACE|NV|P(38)|'+', OC_REPLACE|NV|P(38)|'-',
+	OC_REPLACE|NV|P(38)|'*', OC_REPLACE|NV|P(38)|'/', OC_REPLACE|NV|P(38)|'%', OC_REPLACE|NV|P(38)|'&',
+	OC_BINARY|NV|P(29)|'+',  OC_BINARY|NV|P(29)|'-',  OC_REPLACE|NV|P(38)|'&', OC_BINARY|NV|P(15)|'&',
 	OC_BINARY|NV|P(25)|'/',  OC_BINARY|NV|P(25)|'%',  OC_BINARY|NV|P(15)|'&',  OC_BINARY|NV|P(25)|'*',
 	OC_COMPARE|VV|P(39)|4,   OC_COMPARE|VV|P(39)|3,   OC_COMPARE|VV|P(39)|0,   OC_COMPARE|VV|P(39)|1,
 #define TI_LESS     (OC_COMPARE|VV|P(39)|2)
@@ -1301,7 +1303,7 @@ static uint32_t next_token(uint32_t expected)
 			save_tclass = tc;
 			save_info = t_info;
 			tc = TC_BINOPX;
-			t_info = OC_CONCAT | SS | P(35);
+			t_info = OC_CONCAT | SS | PRECEDENCE(35);
 		}
 
 		t_tclass = tc;
@@ -1361,9 +1363,8 @@ static node *parse_expr(uint32_t term_tc)
 {
 	node sn;
 	node *cn = &sn;
-	node *vn, *glptr;
+	node *glptr;
 	uint32_t tc, expected_tc;
-	var *v;
 
 	debug_printf_parse("%s() term_tc(%x):", __func__, term_tc);
 	debug_parse_print_tc(term_tc);
@@ -1374,11 +1375,12 @@ static node *parse_expr(uint32_t term_tc)
 	expected_tc = TS_OPERAND | TS_UOPPRE | TC_REGEXP | term_tc;
 
 	while (!((tc = next_token(expected_tc)) & term_tc)) {
+		node *vn;
 
 		if (glptr && (t_info == TI_LESS)) {
 			/* input redirection (<) attached to glptr node */
 			debug_printf_parse("%s: input redir\n", __func__);
-			cn = glptr->l.n = new_node(OC_CONCAT | SS | P(37));
+			cn = glptr->l.n = new_node(OC_CONCAT | SS | PRECEDENCE(37));
 			cn->a.n = glptr;
 			expected_tc = TS_OPERAND | TS_UOPPRE;
 			glptr = NULL;
@@ -1390,24 +1392,42 @@ static node *parse_expr(uint32_t term_tc)
 			 * previous operators with higher priority */
 			vn = cn;
 			while (((t_info & PRIMASK) > (vn->a.n->info & PRIMASK2))
-			    || ((t_info == vn->info) && t_info == TI_COLON)
+			    || (t_info == vn->info && t_info == TI_COLON)
 			) {
 				vn = vn->a.n;
 				if (!vn->a.n) syntax_error(EMSG_UNEXP_TOKEN);
 			}
 			if (t_info == TI_TERNARY)
 //TODO: why?
-				t_info += P(6);
+				t_info += PRECEDENCE(6);
 			cn = vn->a.n->r.n = new_node(t_info);
 			cn->a.n = vn->a.n;
 			if (tc & TS_BINOP) {
 				cn->l.n = vn;
-//FIXME: this is the place to detect and reject assignments to non-lvalues.
-//Currently we allow "assignments" to consts and temporaries, nonsense like this:
-// awk 'BEGIN { "qwe" = 1 }'
-// awk 'BEGIN { 7 *= 7 }'
-// awk 'BEGIN { length("qwe") = 1 }'
-// awk 'BEGIN { (1+1) += 3 }'
+
+				/* Prevent:
+				 * awk 'BEGIN { "qwe" = 1 }'
+				 * awk 'BEGIN { 7 *= 7 }'
+				 * awk 'BEGIN { length("qwe") = 1 }'
+				 * awk 'BEGIN { (1+1) += 3 }'
+				 */
+				/* Assignment? (including *= and friends) */
+				if (((t_info & OPCLSMASK) == OC_MOVE)
+				 || ((t_info & OPCLSMASK) == OC_REPLACE)
+				) {
+					debug_printf_parse("%s: MOVE/REPLACE vn->info:%08x\n", __func__, vn->info);
+					/* Left side is a (variable or array element)
+					 * or function argument
+					 * or $FIELD ?
+					 */
+					if ((vn->info & OPCLSMASK) != OC_VAR
+					 && (vn->info & OPCLSMASK) != OC_FNARG
+					 && (vn->info & OPCLSMASK) != OC_FIELD
+					) {
+						syntax_error(EMSG_UNEXP_TOKEN); /* no. bad */
+					}
+				}
+
 				expected_tc = TS_OPERAND | TS_UOPPRE | TC_REGEXP;
 				if (t_info == TI_PGETLINE) {
 					/* it's a pipe */
@@ -1443,6 +1463,8 @@ static node *parse_expr(uint32_t term_tc)
 		/* one should be very careful with switch on tclass -
 		 * only simple tclasses should be used (TC_xyz, not TS_xyz) */
 		switch (tc) {
+			var *v;
+
 		case TC_VARIABLE:
 		case TC_ARRAY:
 			debug_printf_parse("%s: TC_VARIABLE | TC_ARRAY\n", __func__);
@@ -1463,14 +1485,14 @@ static node *parse_expr(uint32_t term_tc)
 		case TC_NUMBER:
 		case TC_STRING:
 			debug_printf_parse("%s: TC_NUMBER | TC_STRING\n", __func__);
-			cn->info = OC_VAR;
+			cn->info = OC_CONST;
 			v = cn->l.v = xzalloc(sizeof(var));
-			if (tc & TC_NUMBER)
+			if (tc & TC_NUMBER) {
 				setvar_i(v, t_double);
-			else {
+			 } else {
 				setvar_s(v, t_string);
-				expected_tc &= ~TC_UOPPOST; /* "str"++ is not allowed */
 			}
+			expected_tc &= ~TC_UOPPOST; /* NUM++, "str"++ not allowed */
 			break;
 
 		case TC_REGEXP:
@@ -3124,6 +3146,8 @@ static var *evaluate(node *op, var *res)
 
 		/* -- recursive node type -- */
 
+		case XC( OC_CONST ):
+			debug_printf_eval("CONST ");
 		case XC( OC_VAR ):
 			debug_printf_eval("VAR\n");
 			L.v = op->l.v;
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index 8ab1c68..cdab93d 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -547,4 +547,9 @@ testing 'awk does not split on CR (char 13)' \
 	'word1 word2 word3\r word2 word3\r\n' \
 	'' 'word1 word2 word3\r'
 
+testing "awk = has higher precedence than == (despite what gawk manpage claims)" \
+	"awk 'BEGIN { v=1; print 2==v; print 2==v=2; print v; print v=3==3; print v}'" \
+	'0\n1\n2\n1\n3\n' \
+	'' ''
+
 exit $FAILCOUNT