shell/math: fix order of expansion of variables to numbers

This fixes arith-assign-in-varexp1.tests

function                                             old     new   delta
evaluate_string                                     1132    1258    +126
arith_lookup_val                                     143       -    -143
arith_apply                                         1132     977    -155
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 126/-298)         Total: -172 bytes

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

3 files changed, 26 insertions, 34 deletions

diff --git a/shell/hush_test/hush-arith/arith-assign-in-varexp1.right b/shell/hush_test/hush-arith/arith-assign-in-varexp1.right
new file mode 100644
index 000000000..1feb307d2
--- /dev/null
+++ b/shell/hush_test/hush-arith/arith-assign-in-varexp1.right
@@ -0,0 +1,2 @@
+7:7
+x=3
diff --git a/shell/hush_test/hush-arith/arith-assign-in-varexp1.tests b/shell/hush_test/hush-arith/arith-assign-in-varexp1.tests
new file mode 100755
index 000000000..fc8ac9d97
--- /dev/null
+++ b/shell/hush_test/hush-arith/arith-assign-in-varexp1.tests
@@ -0,0 +1,9 @@
+exec 2>&1
+a='x=1'
+b='x=2'
+c='x=3'
+# The variables should evaluate immediately when they encountered,
+# not when they go into an operation. Here, order of evaluation
+# of names to numbers should be a,b,c - not b,c,a:
+echo 7:$((a+b*c))
+echo "x=$x"
diff --git a/shell/math.c b/shell/math.c
index 8d0c9dea7..7e2bf5ea5 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -310,7 +310,6 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_
 
         var_or_num_t *top_of_stack;
         arith_t rez;
-        const char *err;
 
         /* There is no operator that can work without arguments */
         if (NUMPTR == numstack)
@@ -324,14 +323,8 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_
                 NUMPTR = expr1 + 1;
                 if (expr1 < numstack) /* Example: $((2:3)) */
                         return "malformed ?: operator";
-                err = arith_lookup_val(math_state, expr1);
-                if (err)
-                        return err;
                 if (expr1->val != 0) /* select expr2 or expr3 */
                         top_of_stack--;
-                err = arith_lookup_val(math_state, top_of_stack);
-                if (err)
-                        return err;
                 expr1->val = top_of_stack->val;
                 expr1->var_name = NULL;
                 return NULL;
@@ -339,24 +332,6 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_
         if (op == TOK_CONDITIONAL) /* Example: $((a ? b)) */
                 return "malformed ?: operator";
 
-        if (PREC(op) < UNARYPREC) {
-                /* In binops a ~ b, variables are resolved left-to-right,
-                 * resolve top_of_stack[-1] _before_ resolving top_of_stack[0]
-                 */
-                if (top_of_stack == numstack) /* need two arguments */
-                        goto syntax_err;
-                /* Unless it is =, resolve top_of_stack[-1] name to value */
-                if (op != TOK_ASSIGN) {
-                        err = arith_lookup_val(math_state, top_of_stack - 1);
-                        if (err)
-                                return err;
-                }
-        }
-        /* Resolve top_of_stack[0] name to value */
-        err = arith_lookup_val(math_state, top_of_stack);
-        if (err)
-                return err;
-
         rez = top_of_stack->val;
         if (op == TOK_UMINUS)
                 rez = -rez;
@@ -372,6 +347,9 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_
                 /* Binary operators */
                 arith_t right_side_val;
 
+                if (top_of_stack == numstack) /* have two arguments? */
+                        goto syntax_err; /* no */
+
                 /* Pop numstack */
                 NUMPTR = top_of_stack; /* this decrements NUMPTR */
                 top_of_stack--; /* now points to left side */
@@ -677,7 +655,16 @@ evaluate_string(arith_state_t *math_state, const char *expr)
                         numstackptr->var_name = alloca(var_name_size);
                         safe_strncpy(numstackptr->var_name, expr, var_name_size);
                         dbg("[%d] var:'%s'", (int)(numstackptr - numstack), numstackptr->var_name);
-                        expr = p;
+                        expr = skip_whitespace(p);
+                        /* If it is not followed by "=" operator... */
+                        if (expr[0] != '=' /* not "=..." */
+                         || expr[1] == '=' /* or "==..." */
+                        ) {
+                                /* Evaluate variable to value */
+                                errmsg = arith_lookup_val(math_state, numstackptr);
+                                if (errmsg)
+                                        goto err_with_custom_msg;
+                        }
  push_num:
                         numstackptr++;
                         lasttok = TOK_NUM;
@@ -819,14 +806,8 @@ evaluate_string(arith_state_t *math_state, const char *expr)
                                 operator prev_op = *--opstackptr;
                                 if (op == TOK_RPAREN) {
                                         if (prev_op == TOK_LPAREN) {
-                                                if (VALID_NAME(numstackptr[-1].var_name)) {
-                                                        /* Expression is (var), lookup now */
-                                                        errmsg = arith_lookup_val(math_state, &numstackptr[-1]);
-                                                        if (errmsg)
-                                                                goto err_with_custom_msg;
-                                                        /* Erase var name: (var) is just a number, for example, (var) = 1 is not valid */
-                                                        numstackptr[-1].var_name = NULL;
-                                                }
+                                                /* Erase var name: (var) is just a number, for example, (var) = 1 is not valid */
+                                                numstackptr[-1].var_name = NULL;
                                                 /* Any operator directly after a
                                                  * close paren should consider itself binary */
                                                 lasttok = TOK_NUM;