checker: disallow indexing a voidptr (#8109)

vlib/v/checker/checker.v

@@ -4718,8 +4718,8 @@ pub fn (mut c Checker) index_expr(mut node ast.IndexExpr) table.Type {
 	typ := c.expr(node.left)
 	node.left_type = typ
 	typ_sym := c.table.get_final_type_symbol(typ)
-	if typ_sym.kind !in [.array, .array_fixed, .string, .map] && !typ.is_ptr() && !(!typ_sym.name[0].is_capital() &&
-		typ_sym.name.ends_with('ptr')) && !typ.has_flag(.variadic) { // byteptr, charptr etc
+	if typ_sym.kind !in [.array, .array_fixed, .string, .map] && !typ.is_ptr() && typ !in [table.byteptr_type, table.charptr_type] &&
+		!typ.has_flag(.variadic) {
 		c.error('type `$typ_sym.name` does not support indexing', node.pos)
 	}
 	if typ_sym.kind == .string && !typ.is_ptr() && node.is_setter {

vlib/v/checker/tests/pointer_ops.out

@@ -32,11 +32,18 @@ vlib/v/checker/tests/pointer_ops.vv:9:4: error: invalid operation: -- (non-numer
     9 |         p--
       |          ~~
    10 |         p -= 3
-   11 |     }
+   11 |         _ = p[3]
 vlib/v/checker/tests/pointer_ops.vv:10:3: error: operator `-=` not defined on left operand type `voidptr`
     8 |         _ = p - 1
     9 |         p--
    10 |         p -= 3
       |         ^
-   11 |     }
-   12 | }
+   11 |         _ = p[3]
+   12 |     }
+vlib/v/checker/tests/pointer_ops.vv:11:8: error: type `voidptr` does not support indexing
+    9 |         p--
+   10 |         p -= 3
+   11 |         _ = p[3]
+      |              ~~~
+   12 |     }
+   13 | }

vlib/v/checker/tests/pointer_ops.vv

@@ -8,5 +8,6 @@ fn test_voidptr() {
 		_ = p - 1
 		p--
 		p -= 3
+		_ = p[3]
 	}
 }