checker: check invalid comptime field name assignment (fix #24415) (#24421)

Author: Delta456

vlib/v/checker/assign.v

@@ -876,13 +876,20 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 							node.pos)
 					}
 				} else {
-					// allow `t.$(field.name) = 0` where `t.$(field.name)` is a enum
 					if c.comptime.comptime_for_field_var != '' && left is ast.ComptimeSelector {
-						field_sym := c.table.sym(c.unwrap_generic(c.comptime.comptime_for_field_type))
+						field_type := c.unwrap_generic(c.comptime.comptime_for_field_type)
+						field_sym := c.table.sym(field_type)
 
+						// allow `t.$(field.name) = 0` where `t.$(field.name)` is a enum
 						if field_sym.kind == .enum && !right_type.is_int() {
 							c.error('enums can only be assigned `int` values', right.pos())
 						}
+						// disallow invalid `t.$(field.name)` type assignment
+						if !c.check_types(field_type, right_type) && !(c.inside_x_matches_type
+							|| field_sym.kind == .enum) {
+							c.error('cannot assign to `${left}`: ${c.expected_msg(right_type,
+								field_type)}', right.pos())
+						}
 					} else {
 						if right_type_unwrapped != ast.void_type {
 							if !var_option || (var_option && right_type_unwrapped != ast.none_type) {

vlib/v/checker/checker.v

@@ -89,6 +89,7 @@ pub mut:
 	inside_fn_arg               bool        // `a`, `b` in `a.f(b)`
 	inside_ct_attr              bool        // true inside `[if expr]`
 	inside_x_is_type            bool        // true inside the Type expression of `if x is Type {`
+	inside_x_matches_type       bool        // true inside the match branch of `match x.type { Type {} }`
 	anon_struct_should_be_mut   bool        // true when `mut var := struct { ... }` is used
 	inside_generic_struct_init  bool
 	inside_integer_literal_cast bool // true inside `int(123)`
@@ -192,6 +193,7 @@ fn (mut c Checker) reset_checker_state_at_start_of_new_file() {
 	c.inside_fn_arg = false
 	c.inside_ct_attr = false
 	c.inside_x_is_type = false
+	c.inside_x_matches_type = false
 	c.inside_integer_literal_cast = false
 	c.skip_flags = false
 	c.fn_level = 0

vlib/v/checker/comptime.v

@@ -274,6 +274,7 @@ fn (mut c Checker) comptime_for(mut node ast.ComptimeFor) {
 			has_different_types := fields.len > 1
 				&& !fields.all(c.check_basic(it.typ, fields[0].typ))
 			for field in fields {
+				prev_inside_x_matches_type := c.inside_x_matches_type
 				c.push_new_comptime_info()
 				c.comptime.inside_comptime_for = true
 				c.table.used_features.comptime_for = true
@@ -301,6 +302,7 @@ fn (mut c Checker) comptime_for(mut node ast.ComptimeFor) {
 					}
 				}
 				c.pop_comptime_info()
+				c.inside_x_matches_type = prev_inside_x_matches_type
 			}
 		} else if node.typ != ast.void_type && c.table.generic_type_names(node.typ).len == 0
 			&& sym.kind != .placeholder {

vlib/v/checker/match.v

@@ -414,6 +414,7 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 				}
 				continue
 			}
+			is_type_node := expr is ast.TypeNode
 			match mut expr {
 				ast.TypeNode {
 					key = c.table.type_to_str(expr.typ)
@@ -438,6 +439,9 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 				c.error('match case `${key}` is handled more than once', branch.pos)
 			}
 			c.expected_type = node.cond_type
+			if is_type_node {
+				c.inside_x_matches_type = true
+			}
 			expr_type := c.expr(mut expr)
 			if expr_type.idx() == 0 {
 				// parser failed, stop checking

vlib/v/checker/tests/assign_enum_at_comptime.out

@@ -1,7 +1,7 @@
 vlib/v/checker/tests/assign_enum_at_comptime.vv:13:21: error: enums can only be assigned `int` values
-   11 |
+   11 | 
    12 |     $for field in TestStruct.fields {
    13 |         t.$(field.name) = '1'
       |                           ~~~
    14 |     }
-   15 | }
+   15 | }

vlib/v/checker/tests/comptime_field_name_assign_incorrect_type_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_field_name_assign_incorrect_type_err.vv:11:25: error: cannot assign to `t.$(field.name)`: expected `int`, not `string`
+    9 |     mut t := T{}
+   10 |     $for field in T.fields {
+   11 |         t.$(field.name) = data[field.name]
+      |                               ~~~~~~~~~~~~
+   12 |     }
+   13 |     return t

vlib/v/checker/tests/comptime_field_name_assign_incorrect_type_err.vv

@@ -0,0 +1,21 @@
+module main
+
+struct Record {
+mut:
+	f1 int
+}
+
+fn map_data[T](data map[string]string) T {
+	mut t := T{}
+	$for field in T.fields {
+		t.$(field.name) = data[field.name]
+	}
+	return t
+}
+
+fn main() {
+	mut data := map[string]string{}
+	data['f1'] = '123'
+	t := map_data[Record](data)
+	println('bug1 : ${t}')
+}

vlib/v/checker/tests/comptime_selector_assign.out

@@ -5,3 +5,10 @@ vlib/v/checker/tests/comptime_selector_assign.vv:18:24: error: mismatched types:
       |                                 ^
    19 |         }
    20 |     }
+vlib/v/checker/tests/comptime_selector_assign.vv:18:24: error: cannot assign to `typ.$(field.name)`: expected `string`, not `int literal`
+   16 |                 typ.$(field.name) = 2
+   17 |             }
+   18 |             typ.$(field.name) = 3
+      |                                 ^
+   19 |         }
+   20 |     }