From 20294fab5d934a4cb4178e651ef51f8e6671762e Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Tue, 3 Dec 2024 20:00:17 -0300
Subject: [PATCH] checker: fix missing checker for cast from mut var to non-ptr
 type (fix #23017) (#23056)

---
 vlib/v/checker/checker.v                      | 10 ++++
 .../tests/cast_to_concrete_mut_err.out        | 14 +++++
 .../checker/tests/cast_to_concrete_mut_err.vv | 58 +++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 vlib/v/checker/tests/cast_to_concrete_mut_err.out
 create mode 100644 vlib/v/checker/tests/cast_to_concrete_mut_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index dc752671d..699b21d72 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3614,6 +3614,16 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		c.error('cannot cast `${ft}` ${kind_name} value to `${tt}`, use `${node.expr} as ${tt}` instead',
 			node.pos)
 	}
+	if from_sym.language == .v && from_type.is_ptr() && !to_type.is_ptr() && !final_to_type.is_ptr()
+		&& !node.expr.is_auto_deref_var() && final_to_sym.kind == .struct
+		&& final_from_sym.kind == .struct {
+		if c.check_struct_signature(final_from_sym.info as ast.Struct, final_to_sym.info as ast.Struct) {
+			ft := c.table.type_to_str(from_type)
+			tt := c.table.type_to_str(to_type)
+			c.error('cannot cast `${ft}` to `${tt}`, you must dereference it first (e.g. ${tt}(*var))',
+				node.pos)
+		}
+	}
 
 	if node.has_arg {
 		c.expr(mut node.arg)
diff --git a/vlib/v/checker/tests/cast_to_concrete_mut_err.out b/vlib/v/checker/tests/cast_to_concrete_mut_err.out
new file mode 100644
index 000000000..ef940f364
--- /dev/null
+++ b/vlib/v/checker/tests/cast_to_concrete_mut_err.out
@@ -0,0 +1,14 @@
+vlib/v/checker/tests/cast_to_concrete_mut_err.vv:37:12: warning: casting `&Message` to `&LocalMessageType` is only allowed in `unsafe` code
+   35 |     if mut mdef is Message {
+   36 |         mut a := LocalMessageType(*mdef)
+   37 |         mut b := &LocalMessageType(mdef)
+      |                  ~~~~~~~~~~~~~~~~~~~~~~~
+   38 |         mut c := LocalMessageType(mdef)
+   39 |
+vlib/v/checker/tests/cast_to_concrete_mut_err.vv:38:12: error: cannot cast `&Message` to `LocalMessageType`, you must dereference it first (e.g. LocalMessageType(*var))
+   36 |         mut a := LocalMessageType(*mdef)
+   37 |         mut b := &LocalMessageType(mdef)
+   38 |         mut c := LocalMessageType(mdef)
+      |                  ~~~~~~~~~~~~~~~~~~~~~~
+   39 | 
+   40 |         dump(a)
diff --git a/vlib/v/checker/tests/cast_to_concrete_mut_err.vv b/vlib/v/checker/tests/cast_to_concrete_mut_err.vv
new file mode 100644
index 000000000..f911d8558
--- /dev/null
+++ b/vlib/v/checker/tests/cast_to_concrete_mut_err.vv
@@ -0,0 +1,58 @@
+module main
+
+pub struct Message {
+pub mut:
+	text string = 'Init'
+	m2   ?&Message
+}
+
+pub fn (mut m Message) update_text(new_text string) {
+	m.text = new_text
+}
+
+pub fn (mut m Message) update_ext_text(new_text string) {
+	m.m2?.text = new_text
+}
+
+type LocalMessageType = Message
+
+interface IMessage {
+mut:
+	text string
+	update_text(new_text string)
+}
+
+struct App {
+mut:
+	message &IMessage
+}
+
+pub fn (mut m LocalMessageType) update_text_externally(new_text string) {
+	m.text = new_text
+}
+
+fn print_message(mut mdef IMessage) {
+	if mut mdef is Message {
+		mut a := LocalMessageType(*mdef)
+		mut b := &LocalMessageType(mdef)
+		mut c := LocalMessageType(mdef)
+
+		dump(a)
+		dump(b)
+		dump(c)
+	}
+}
+
+fn test_main() {
+	mut m2 := &Message{
+		text: 'Init External'
+	}
+	mut mdef := &Message{
+		text: 'Init'
+		m2:   m2
+	}
+	mut app := &App{
+		message: mdef
+	}
+	print_message(mut app.message)
+}
-- 
2.39.5