gen: fix slicing mutable arguments (#6596)

vlib/v/checker/checker.v

@@ -3666,18 +3666,7 @@ pub fn (mut c Checker) index_expr(mut node ast.IndexExpr) table.Type {
 			c.warn('pointer indexing is only allowed in `unsafe` blocks', node.pos)
 		}
 	}
-	if node.index !is ast.RangeExpr { // [1]
+	if node.index is ast.RangeExpr as range { // [1..2]
-		index_type := c.expr(node.index)
-		c.check_index_type(typ_sym, index_type, node.pos)
-		if typ_sym.kind == .map && index_type.idx() != table.string_type_idx {
-			c.error('non-string map index (map type `$typ_sym.source_name`)', node.pos)
-		}
-		value_type := c.table.value_type(typ)
-		if value_type != table.void_type {
-			return value_type
-		}
-	} else { // [1..2]
-		range := node.index as ast.RangeExpr
 		if range.has_low {
 			index_type := c.expr(range.low)
 			c.check_index_type(typ_sym, index_type, node.pos)
@@ -3693,6 +3682,17 @@ pub fn (mut c Checker) index_expr(mut node ast.IndexExpr) table.Type {
 			idx := c.table.find_or_register_array(elem_type, 1, c.mod)
 			return table.new_type(idx)
 		}
+		return typ.set_nr_muls(0)
+	} else { // [1]
+		index_type := c.expr(node.index)
+		c.check_index_type(typ_sym, index_type, node.pos)
+		if typ_sym.kind == .map && index_type.idx() != table.string_type_idx {
+			c.error('non-string map index (map type `$typ_sym.source_name`)', node.pos)
+		}
+		value_type := c.table.value_type(typ)
+		if value_type != table.void_type {
+			return value_type
+		}
 	}
 	return typ
 }

vlib/v/gen/cgen.v

@@ -2228,7 +2228,6 @@ fn (mut g Gen) expr(node ast.Expr) {
 		}
 		ast.SelectorExpr {
 			if node.expr is ast.TypeOf as left {
-				// typeof(expr).name
 				g.typeof_name(left)
 				return
 			}

vlib/v/tests/array_mut_slicing_test.v

@@ -1,8 +0,0 @@
-fn array_mut_slice(mut a []int) {
-	assert a[1..3].map(it) == [3, 5]
-}
-
-fn test_array_mut_slice() {
-	mut a := [1, 3, 5, 7, 9]
-	array_mut_slice(mut a)
-}

vlib/v/tests/array_slice_clone_test.v

@@ -1,11 +0,0 @@
-fn test_array_slice_clone() {
-	arr := [1, 2, 3, 4, 5]
-	cl := arr[1..].clone()
-	assert cl == [2, 3, 4, 5]
-}
-
-fn test_array_slice_clone2() {
-	arr := [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
-	cl := arr[1..].clone()[2..].clone()
-	assert cl == [4, 5, 6, 7, 8, 9, 10]
-}

vlib/v/tests/array_slice_test.v

@@ -0,0 +1,31 @@
+fn array_mut_slice(mut a []int) {
+	assert a[1..3].map(it) == [3, 5]
+}
+
+fn test_array_mut_slice() {
+	mut a := [1, 3, 5, 7, 9]
+	array_mut_slice(mut a)
+}
+
+fn test_array_slice_clone() {
+	arr := [1, 2, 3, 4, 5]
+	cl := arr[1..].clone()
+	assert cl == [2, 3, 4, 5]
+}
+
+fn test_array_slice_clone2() {
+	arr := [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+	cl := arr[1..].clone()[2..].clone()
+	assert cl == [4, 5, 6, 7, 8, 9, 10]
+}
+
+fn access_slice_attribute(mut arr []int) int {
+	slice := arr[..arr.len - 1]
+	return slice.len
+}
+
+fn test_access_slice_attribute() {
+	mut arr := [1, 2, 3, 4, 5]
+	assert access_slice_attribute(mut arr) == 4
+}
+