From dddcf298026e188c173342a383eb8c71f31fe274 Mon Sep 17 00:00:00 2001
From: kbkpbot <kbkpbot@sina.com>
Date: Sun, 16 Nov 2025 13:28:43 +0800
Subject: [PATCH] checker: disallow deference of nil (fix #25740) (#25746)

---
 vlib/v/checker/checker.v                          | 3 +++
 vlib/v/checker/tests/unsafe_deference_nil_err.out | 6 ++++++
 vlib/v/checker/tests/unsafe_deference_nil_err.vv  | 1 +
 3 files changed, 10 insertions(+)
 create mode 100644 vlib/v/checker/tests/unsafe_deference_nil_err.out
 create mode 100644 vlib/v/checker/tests/unsafe_deference_nil_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index cee396f1e..4943f426e 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -5033,6 +5033,9 @@ fn (mut c Checker) prefix_expr(mut node ast.PrefixExpr) ast.Type {
 		if right_type.is_voidptr() {
 			c.error('cannot dereference to void', node.pos)
 		}
+		if right_type == ast.nil_type {
+			c.error('cannot deference a `nil` pointer', node.right.pos())
+		}
 		if mut expr is ast.Ident {
 			if var := expr.scope.find_var('${expr.name}') {
 				if var.expr is ast.UnsafeExpr {
diff --git a/vlib/v/checker/tests/unsafe_deference_nil_err.out b/vlib/v/checker/tests/unsafe_deference_nil_err.out
new file mode 100644
index 000000000..daefa7cea
--- /dev/null
+++ b/vlib/v/checker/tests/unsafe_deference_nil_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/unsafe_deference_nil_err.vv:1:1: warning: unused variable: `a`
+    1 | a := unsafe { *nil }
+      | ^
+vlib/v/checker/tests/unsafe_deference_nil_err.vv:1:16: error: cannot deference a `nil` pointer
+    1 | a := unsafe { *nil }
+      |                ~~~
diff --git a/vlib/v/checker/tests/unsafe_deference_nil_err.vv b/vlib/v/checker/tests/unsafe_deference_nil_err.vv
new file mode 100644
index 000000000..3af819d13
--- /dev/null
+++ b/vlib/v/checker/tests/unsafe_deference_nil_err.vv
@@ -0,0 +1 @@
+a := unsafe { *nil }
-- 
2.39.5