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 c49ad6e02..0f062dcdb 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 8ab1c6891..cdab93d21 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