shell: handle $((NUM++...) like bash does. Closes 10706

function                                             old     new   delta
evaluate_string                                      680     729     +49

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

shell/ash_test/ash-arith/arith-postinc.right

@@ -0,0 +1,5 @@
+1 1
+1 1
+1 1
+1 1
+Ok:0

shell/ash_test/ash-arith/arith-postinc.tests

@@ -0,0 +1,5 @@
+echo 1 $((0++1))
+echo 1 $((0--1))
+x=-1; echo 1 $((0-$x))
+x=+1; echo 1 $((0+$x))
+echo Ok:$?

shell/ash_test/ash-arith/arith.right

@@ -126,6 +126,10 @@ ghi
 ./arith2.sub: line 5: arithmetic syntax error
 5 5
 1 1
+6 6
+2 2
+3 3
+1 1
 4 4
 0 0
 ./arith2.sub: line 42: arithmetic syntax error

shell/ash_test/ash-arith/arith2.sub

@@ -23,14 +23,14 @@
 echo 5 $(( 4 + ++a ))
 echo 1 $a
 
-# ash doesn't handle it right...
-#ash# echo 6 $(( 4+++a ))
-#ash# echo 2 $a
+# this is treated as 4 + ++a
+echo 6 $(( 4+++a ))
+echo 2 $a
       a=2
 
-# ash doesn't handle it right...
-#ash# echo 3 $(( 4---a ))
-#ash# echo 1 $a
+# this is treated as 4 - --a
+echo 3 $(( 4---a ))
+echo 1 $a
       a=1
 
 echo 4 $(( 4 - -- a ))

shell/hush_test/hush-arith/arith-postinc.right

@@ -0,0 +1,5 @@
+1 1
+1 1
+1 1
+1 1
+Ok:0

shell/hush_test/hush-arith/arith-postinc.tests

@@ -0,0 +1,5 @@
+echo 1 $((0++1))
+echo 1 $((0--1))
+x=-1; echo 1 $((0-$x))
+x=+1; echo 1 $((0+$x))
+echo Ok:$?

shell/hush_test/hush-arith/arith.right

@@ -135,6 +135,10 @@ hush: arithmetic syntax error
 hush: arithmetic syntax error
 5 5
 1 1
+6 6
+2 2
+3 3
+1 1
 4 4
 0 0
 hush: arithmetic syntax error

shell/hush_test/hush-arith/arith2.sub

@@ -23,14 +23,14 @@
 echo 5 $(( 4 + ++a ))
 echo 1 $a
 
-# ash doesn't handle it right...
-#ash# echo 6 $(( 4+++a ))
-#ash# echo 2 $a
+# this is treated as 4 + ++a
+echo 6 $(( 4+++a ))
+echo 2 $a
       a=2
 
-# ash doesn't handle it right...
-#ash# echo 3 $(( 4---a ))
-#ash# echo 1 $a
+# this is treated as 4 - --a
+echo 3 $(( 4---a ))
+echo 1 $a
       a=1
 
 echo 4 $(( 4 - -- a ))

shell/math.c

@@ -598,10 +598,24 @@ evaluate_string(arith_state_t *math_state, const char *expr)
 		}
 
 		/* Should be an operator */
+
+		/* Special case: NUM-- and NUM++ are not recognized if NUM
+		 * is a literal number, not a variable. IOW:
+		 * "a+++v" is a++ + v.
+		 * "7+++v" is 7 + ++v, not 7++ + v.
+		 */
+		if (lasttok == TOK_NUM && !numstackptr[-1].var /* number literal */
+		 && (expr[0] == '+' || expr[0] == '-')
+		 && (expr[1] == expr[0])
+		) {
+			//bb_error_msg("special %c%c", expr[0], expr[0]);
+			op = (expr[0] == '+' ? TOK_ADD : TOK_SUB);
+			expr += 1;
+			goto tok_found1;
+		}
+
 		p = op_tokens;
 		while (1) {
-// TODO: bash allows 7+++v, treats it as 7 + ++v
-// we treat it as 7++ + v and reject
 			/* Compare expr to current op_tokens[] element */
 			const char *e = expr;
 			while (1) {
@@ -627,6 +641,7 @@ evaluate_string(arith_state_t *math_state, const char *expr)
 		}
  tok_found:
 		op = p[1]; /* fetch TOK_foo value */
+ tok_found1:
 		/* NB: expr now points past the operator */
 
 		/* post grammar: a++ reduce to num */