checker: disallow invalid pointer arithmetic (#10888)

vlib/v/checker/check_types.v

@@ -195,13 +195,13 @@ fn (mut c Checker) check_shift(left_type ast.Type, right_type ast.Type, left_pos
 }
 
 pub fn (mut c Checker) promote(left_type ast.Type, right_type ast.Type) ast.Type {
-	if left_type.is_ptr() || left_type.is_pointer() {
+	if left_type.is_any_kind_of_pointer() {
 		if right_type.is_int() {
 			return left_type
 		} else {
 			return ast.void_type
 		}
-	} else if right_type.is_ptr() || right_type.is_pointer() {
+	} else if right_type.is_any_kind_of_pointer() {
 		if left_type.is_int() {
 			return right_type
 		} else {

vlib/v/checker/checker.v

@@ -1241,12 +1241,20 @@ pub fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 	left_pos := node.left.position()
 	right_pos := node.right.position()
 	left_right_pos := left_pos.extend(right_pos)
-	if (left_type.is_ptr() || left_sym.is_pointer()) && node.op in [.plus, .minus] {
+	if left_type.is_any_kind_of_pointer()
-		if !c.inside_unsafe && !node.left.is_auto_deref_var() && !node.right.is_auto_deref_var() {
+		&& node.op in [.plus, .minus, .mul, .div, .mod, .xor, .amp, .pipe] {
-			c.warn('pointer arithmetic is only allowed in `unsafe` blocks', left_pos)
+		if (right_type.is_any_kind_of_pointer() && node.op != .minus)
-		}
+			|| (!right_type.is_any_kind_of_pointer() && node.op !in [.plus, .minus]) {
-		if left_type == ast.voidptr_type {
+			left_name := c.table.type_to_str(left_type)
-			c.error('`$node.op` cannot be used with `voidptr`', left_pos)
+			right_name := c.table.type_to_str(right_type)
+			c.error('invalid operator `$node.op` to `$left_name` and `$right_name`', left_right_pos)
+		} else if node.op in [.plus, .minus] {
+			if !c.inside_unsafe && !node.left.is_auto_deref_var() && !node.right.is_auto_deref_var() {
+				c.warn('pointer arithmetic is only allowed in `unsafe` blocks', left_right_pos)
+			}
+			if left_type == ast.voidptr_type {
+				c.error('`$node.op` cannot be used with `voidptr`', left_pos)
+			}
 		}
 	}
 	mut return_type := left_type
@@ -1408,7 +1416,15 @@ pub fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 					c.error('mismatched types `$left_name` and `$right_name`', left_right_pos)
 				}
 			} else {
-				promoted_type := c.promote(c.table.unalias_num_type(left_type), c.table.unalias_num_type(right_type))
+				unaliased_left_type := c.table.unalias_num_type(left_type)
+				unalias_right_type := c.table.unalias_num_type(right_type)
+				mut promoted_type := c.promote(unaliased_left_type, unalias_right_type)
+				// substract pointers is allowed in unsafe block
+				is_allowed_pointer_arithmetic := left_type.is_any_kind_of_pointer()
+					&& right_type.is_any_kind_of_pointer() && node.op == .minus
+				if is_allowed_pointer_arithmetic {
+					promoted_type = ast.int_type
+				}
 				if promoted_type.idx() == ast.void_type_idx {
 					left_name := c.table.type_to_str(left_type)
 					right_name := c.table.type_to_str(right_type)

vlib/v/checker/tests/disallow_pointer_arithmetic_err.out

@@ -0,0 +1,34 @@
+vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv:4:7: error: invalid operator `+` to `&int` and `&int`
+    2 |     x := 5
+    3 |     p := &x
+    4 |     _ := p + p //should be error
+      |          ~~~~~
+    5 |     _ := p * p //should be error
+    6 |     _ := p * 2 //should be error
+vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv:5:7: error: invalid operator `*` to `&int` and `&int`
+    3 |     p := &x
+    4 |     _ := p + p //should be error
+    5 |     _ := p * p //should be error
+      |          ~~~~~
+    6 |     _ := p * 2 //should be error
+    7 |     _ := p + 5 //OK but only in unsafe block, r is *int
+vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv:6:7: error: invalid operator `*` to `&int` and `int literal`
+    4 |     _ := p + p //should be error
+    5 |     _ := p * p //should be error
+    6 |     _ := p * 2 //should be error
+      |          ~~~~~
+    7 |     _ := p + 5 //OK but only in unsafe block, r is *int
+    8 |     _ := p - p //OK even in safe code, but n should be isize
+vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv:7:7: error: pointer arithmetic is only allowed in `unsafe` blocks
+    5 |     _ := p * p //should be error
+    6 |     _ := p * 2 //should be error
+    7 |     _ := p + 5 //OK but only in unsafe block, r is *int
+      |          ~~~~~
+    8 |     _ := p - p //OK even in safe code, but n should be isize
+    9 | }
+vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv:8:7: error: pointer arithmetic is only allowed in `unsafe` blocks
+    6 |     _ := p * 2 //should be error
+    7 |     _ := p + 5 //OK but only in unsafe block, r is *int
+    8 |     _ := p - p //OK even in safe code, but n should be isize
+      |          ~~~~~
+    9 | }

vlib/v/checker/tests/disallow_pointer_arithmetic_err.vv

@@ -0,0 +1,9 @@
+fn main() {
+	x := 5
+	p := &x
+	_ := p + p //should be error
+	_ := p * p //should be error
+	_ := p * 2 //should be error
+	_ := p + 5 //OK but only in unsafe block, r is *int
+	_ := p - p //OK even in safe code, but n should be isize
+}

vlib/v/checker/tests/mismatched_ptr_op_ptr.out

@@ -5,7 +5,7 @@ vlib/v/checker/tests/mismatched_ptr_op_ptr.vv:5:17: error: mismatched types `&st
       |                 ~~~
     6 |         println(b+b)
     7 |     }
-vlib/v/checker/tests/mismatched_ptr_op_ptr.vv:6:17: error: mismatched types `&string` and `&string`
+vlib/v/checker/tests/mismatched_ptr_op_ptr.vv:6:17: error: invalid operator `+` to `&string` and `&string`
     4 |         b := &a
     5 |         println(b+*b)
     6 |         println(b+b)

vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.out

@@ -16,13 +16,13 @@ vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:11:14: error
     9 | fn test_ptr_infix() {
    10 |     v := 4
    11 |     mut q := &v - 1
-      |              ^
+      |              ~~~~~~
    12 |     q = q + 3
    13 |     _ := q
 vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:12:9: error: pointer arithmetic is only allowed in `unsafe` blocks
    10 |     v := 4
    11 |     mut q := &v - 1
    12 |     q = q + 3
-      |         ^
+      |         ~~~~~
    13 |     _ := q
    14 |     _ := v

vlib/v/tests/pointer_arithmetic_test.v

@@ -0,0 +1,6 @@
+fn test_strings() {
+	s := 'hi'
+	mut p := unsafe { s.str + 1 }
+	n := unsafe { p - s.str }
+	assert typeof(n).name == 'int'
+}