From 3ced22e21bbe424ecf49ff21af643e789d665106 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 14:06:12 +0300
Subject: [PATCH] cgen: struct pointer comparison with nil causes segfault
 (fixes #26370)

---
 vlib/v/gen/c/infix.v                          | 82 ++++++++++++++++---
 .../struct_pointer_nil_comparison_test.v      | 23 ++++++
 2 files changed, 92 insertions(+), 13 deletions(-)
 create mode 100644 vlib/v/tests/structs/struct_pointer_nil_comparison_test.v

diff --git a/vlib/v/gen/c/infix.v b/vlib/v/gen/c/infix.v
index b8f801982..a4c0351cf 100644
--- a/vlib/v/gen/c/infix.v
+++ b/vlib/v/gen/c/infix.v
@@ -329,20 +329,18 @@ fn (mut g Gen) infix_expr_eq_op(node ast.InfixExpr) {
 			}
 			.struct {
 				ptr_typ := g.equality_fn(left.unaliased)
-				if node.op == .ne {
-					g.write('!')
-				}
-				g.write('${ptr_typ}_struct_eq(')
-				if left.typ.is_ptr() {
-					g.write('*'.repeat(left.typ.nr_muls()))
-				}
-				g.expr(node.left)
-				g.write(', ')
-				if right.typ.is_ptr() {
-					g.write('*'.repeat(right.typ.nr_muls()))
+				if left.typ.is_ptr() || right.typ.is_ptr() {
+					g.gen_struct_pointer_eq_op(node, left_type, right_type, ptr_typ)
+				} else {
+					if node.op == .ne {
+						g.write('!')
+					}
+					g.write('${ptr_typ}_struct_eq(')
+					g.expr(node.left)
+					g.write(', ')
+					g.expr(node.right)
+					g.write(')')
 				}
-				g.expr(node.right)
-				g.write(')')
 			}
 			.sum_type {
 				ptr_typ := g.equality_fn(left.unaliased)
@@ -433,6 +431,64 @@ fn (mut g Gen) infix_expr_eq_op(node ast.InfixExpr) {
 	}
 }
 
+fn (mut g Gen) gen_struct_pointer_eq_op(node ast.InfixExpr, left_type ast.Type, right_type ast.Type, ptr_typ string) {
+	mut stmt_str := ''
+	mut restore_stmt := false
+	mut left_expr := ''
+	mut right_expr := ''
+	if left_type.is_ptr() && !node.left.is_lvalue() {
+		if !restore_stmt {
+			stmt_str = g.go_before_last_stmt().trim_space()
+			g.empty_line = true
+			restore_stmt = true
+		}
+		mut left_tmp := g.new_ctemp_var(node.left, left_type)
+		g.gen_ctemp_var(mut left_tmp)
+		left_expr = left_tmp.name
+	} else {
+		left_expr = g.expr_string(node.left)
+	}
+	if right_type.is_ptr() && !node.right.is_lvalue() {
+		if !restore_stmt {
+			stmt_str = g.go_before_last_stmt().trim_space()
+			g.empty_line = true
+			restore_stmt = true
+		}
+		mut right_tmp := g.new_ctemp_var(node.right, right_type)
+		g.gen_ctemp_var(mut right_tmp)
+		right_expr = right_tmp.name
+	} else {
+		right_expr = g.expr_string(node.right)
+	}
+	if restore_stmt {
+		g.write(stmt_str)
+	}
+	if node.op == .ne {
+		g.write('!')
+	}
+	g.write('(')
+	if left_type.is_ptr() && right_type.is_ptr() {
+		g.write('${left_expr} == ${right_expr} || (${left_expr} != 0 && ${right_expr} != 0 && ')
+		g.write('${ptr_typ}_struct_eq(')
+		g.write('*'.repeat(left_type.nr_muls()))
+		g.write(left_expr)
+		g.write(', ')
+		g.write('*'.repeat(right_type.nr_muls()))
+		g.write(right_expr)
+		g.write('))')
+	} else if left_type.is_ptr() {
+		g.write('${left_expr} != 0 && ${ptr_typ}_struct_eq(')
+		g.write('*'.repeat(left_type.nr_muls()))
+		g.write(left_expr)
+		g.write(', ${right_expr})')
+	} else {
+		g.write('${right_expr} != 0 && ${ptr_typ}_struct_eq(${left_expr}, ')
+		g.write('*'.repeat(right_type.nr_muls()))
+		g.write('${right_expr})')
+	}
+	g.write(')')
+}
+
 // infix_expr_cmp_op generates code for `<`, `<=`, `>`, `>=`
 // It handles operator overloading when necessary
 fn (mut g Gen) infix_expr_cmp_op(node ast.InfixExpr) {
diff --git a/vlib/v/tests/structs/struct_pointer_nil_comparison_test.v b/vlib/v/tests/structs/struct_pointer_nil_comparison_test.v
new file mode 100644
index 000000000..a7f01fb89
--- /dev/null
+++ b/vlib/v/tests/structs/struct_pointer_nil_comparison_test.v
@@ -0,0 +1,23 @@
+struct PtrNilFoo {
+	x int
+}
+
+fn test_struct_pointer_comparison_with_nil_is_nil_safe() {
+	p := &PtrNilFoo{
+		x: 42
+	}
+	same_value := &PtrNilFoo{
+		x: 42
+	}
+	other := &PtrNilFoo{
+		x: 7
+	}
+	nil_p := unsafe { &PtrNilFoo(nil) }
+	nil_q := unsafe { &PtrNilFoo(nil) }
+
+	assert p == same_value
+	assert p != other
+	assert p != nil_p
+	assert nil_p != p
+	assert nil_p == nil_q
+}
-- 
2.39.5