From f8ba4ba1fef7b45a042a5c836f6872c4e2b22d7d Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Wed, 13 Sep 2023 14:10:10 +0530
Subject: [PATCH] checker: disallow alias ptr cast of a map value (#19336)

---
 vlib/v/checker/checker.v                                   | 5 ++++-
 vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.out | 6 ++++++
 vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv  | 5 +++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.out
 create mode 100644 vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 6ba7795ba..153514fca 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3177,6 +3177,10 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		c.error('casting a function value from one function signature, to another function signature, should be done inside `unsafe{}` blocks',
 			node.pos)
 	}
+	if to_type.is_ptr() && to_sym.kind == .alias && from_sym.kind == .map {
+		c.error('cannot cast to alias pointer `${c.table.type_to_str(to_type)}` because `${c.table.type_to_str(from_type)}` is a value',
+			node.pos)
+	}
 
 	if to_type == ast.string_type {
 		if from_type in [ast.u8_type, ast.bool_type] {
@@ -3281,7 +3285,6 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 				}
 			}
 		}
-		// don't allow casting `string` to `enum`, and suggest using `enum_name.type_to_string(str)` instead
 		if mut node.expr is ast.StringLiteral {
 			c.add_error_detail('use ${c.table.type_to_str(node.typ)}.from_string(\'${node.expr.val}\') instead')
 			c.error('cannot cast `string` to `enum`', node.pos)
diff --git a/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.out b/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.out
new file mode 100644
index 000000000..cee24aaee
--- /dev/null
+++ b/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv:4:7: error: cannot cast to alias pointer `&FooMap` because `map[string]int` is a value
+    2 | 
+    3 | fn main() {
+    4 |     _ := &FooMap(map[string]int{})
+      |          ~~~~~~~~~~~~~~~~~~~~~~~~~
+    5 | }
diff --git a/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv b/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv
new file mode 100644
index 000000000..a76977478
--- /dev/null
+++ b/vlib/v/checker/tests/invalid_alias_ptr_cast_on_map_err.vv
@@ -0,0 +1,5 @@
+type FooMap = map[string]int
+
+fn main() {
+	_ := &FooMap(map[string]int{})
+}
-- 
2.39.5