From dc222b6ca61eda64830eb02709fdfc5a5e301388 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Fri, 14 Mar 2025 04:22:54 -0300
Subject: [PATCH] checker: add missing check for casting generic type to
 literal values (#23915)

---
 vlib/v/checker/checker.v                  | 6 ++++++
 vlib/v/checker/tests/cast_generic_err.out | 6 ++++++
 vlib/v/checker/tests/cast_generic_err.vv  | 9 +++++++++
 3 files changed, 21 insertions(+)
 create mode 100644 vlib/v/checker/tests/cast_generic_err.out
 create mode 100644 vlib/v/checker/tests/cast_generic_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 591da61af..c434fa09f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3585,6 +3585,12 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		c.error('cannot cast type `${ft}` to `${tt}`', node.pos)
 	}
 
+	// T(0) where T is array or map
+	if node.typ.has_flag(.generic) && to_sym.kind in [.array, .map, .array_fixed]
+		&& node.expr.is_literal() {
+		c.error('cannot cast literal value to ${to_sym.name} type', node.pos)
+	}
+
 	if to_sym.kind == .enum && !(c.inside_unsafe || c.file.is_translated) && from_sym.is_int() {
 		c.error('casting numbers to enums, should be done inside `unsafe{}` blocks', node.pos)
 	}
diff --git a/vlib/v/checker/tests/cast_generic_err.out b/vlib/v/checker/tests/cast_generic_err.out
new file mode 100644
index 000000000..87913890f
--- /dev/null
+++ b/vlib/v/checker/tests/cast_generic_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/cast_generic_err.vv:2:7: error: cannot cast literal value to [2]u8 type
+    1 | fn decode[T]() {
+    2 |     _ := T(0)
+      |          ~~~~
+    3 | }
+    4 |
diff --git a/vlib/v/checker/tests/cast_generic_err.vv b/vlib/v/checker/tests/cast_generic_err.vv
new file mode 100644
index 000000000..47ecb119d
--- /dev/null
+++ b/vlib/v/checker/tests/cast_generic_err.vv
@@ -0,0 +1,9 @@
+fn decode[T]() {
+	_ := T(0)
+}
+
+fn main() {
+	decode[[2]u8]()
+	decode[[]u8]()
+	decode[map[int]u8]()
+}
-- 
2.39.5