checker, cgen: fix sumtype smartcasted var as inherited var (fix #23716) (#23731)

Author: felipensp

vlib/v/checker/fn.v

@@ -634,8 +634,13 @@ fn (mut c Checker) anon_fn(mut node ast.AnonFn) ast.Type {
 			c.error('original `${parent_var.name}` is immutable, declare it with `mut` to make it mutable',
 				var.pos)
 		}
+		ptyp := if parent_var.smartcasts.len > 0 {
+			parent_var.smartcasts.last()
+		} else {
+			parent_var.typ
+		}
 		if parent_var.typ != ast.no_type {
-			parent_var_sym := c.table.final_sym(parent_var.typ)
+			parent_var_sym := c.table.final_sym(ptyp)
 			if parent_var_sym.info is ast.FnType {
 				ret_typ := c.unwrap_generic(parent_var_sym.info.func.return_type)
 				if ret_typ.has_flag(.generic) {
@@ -663,7 +668,7 @@ fn (mut c Checker) anon_fn(mut node ast.AnonFn) ast.Type {
 				var.typ = parent_var.expr.expr_type.clear_option_and_result()
 			}
 		} else {
-			var.typ = parent_var.typ
+			var.typ = ptyp
 		}
 		if var.typ.has_flag(.generic) {
 			has_generic = true

vlib/v/gen/c/fn.v

@@ -662,13 +662,20 @@ fn (mut g Gen) gen_anon_fn(mut node ast.AnonFn) {
 				g.writeln('.${var_name} = string_clone(${var_name}),')
 			} else {
 				mut is_auto_heap := false
+				mut field_name := ''
 				if obj := node.decl.scope.parent.find(var.name) {
 					if obj is ast.Var {
 						is_auto_heap = !obj.is_stack_obj && obj.is_auto_heap
+						if obj.smartcasts.len > 0 {
+							if g.table.type_kind(obj.typ) == .sum_type {
+								cast_sym := g.table.sym(obj.smartcasts.last())
+								field_name += '._${cast_sym.cname}'
+							}
+						}
 					}
 				}
-				if is_auto_heap && !is_ptr {
-					g.writeln('.${var_name} = *${var_name},')
+				if (is_auto_heap && !is_ptr) || field_name != '' {
+					g.writeln('.${var_name} = *${var_name}${field_name},')
 				} else {
 					g.writeln('.${var_name} = ${var_name},')
 				}

vlib/v/tests/sumtypes/sumtype_inherited_var_test.v

@@ -0,0 +1,26 @@
+struct Aa {
+	a int
+}
+
+struct Bb {
+	b int
+}
+
+type Type = Aa | Bb
+
+fn test_main() {
+	t := Type(Aa{
+		a: 2
+	})
+	match t {
+		Aa {
+			assert t.a == 2
+			func := fn [t] () {
+				assert typeof(t).name == 'Aa'
+				assert t.a == 2
+			}
+			func()
+		}
+		Bb {}
+	}
+}