From 36e31d6908311b87e0d447bbcbc9ac3b96bd88e0 Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Wed, 3 Jul 2024 01:35:20 +0530
Subject: [PATCH] checker: disallow nil in non-nil arrays and vice versa 
 (#21786)

---
 vlib/v/checker/check_types.v                       | 14 ++++++++++++++
 .../tests/non_nil_array_with_nil_element_err.out   |  8 ++++++++
 .../tests/non_nil_array_with_nil_element_err.vv    |  2 ++
 .../struct_field_assign_internal_types_nil_err.out |  7 +++++++
 vlib/v/tests/cast_fixed_array_to_ptr_ptr_test.v    |  2 +-
 5 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/non_nil_array_with_nil_element_err.out
 create mode 100644 vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv

diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 028f5b7df47e1e..3ee37d2f99f389 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -129,6 +129,20 @@ fn (mut c Checker) check_types(got ast.Type, expected ast.Type) bool {
 			return true
 		}
 	}
+
+	if (exp_idx == ast.nil_type_idx && got_idx == ast.string_type_idx)
+		|| (got_idx == ast.nil_type_idx && exp_idx == ast.string_type_idx) {
+		got_sym := c.table.sym(got)
+		exp_sym := c.table.sym(expected)
+
+		if expected.is_ptr() || got.is_ptr() {
+			return true
+		}
+		if got_sym.language != .c || exp_sym.language != .c {
+			return false
+		}
+	}
+
 	// allow direct int-literal assignment for pointers for now
 	// maybe in the future options should be used for that
 	if expected.is_any_kind_of_pointer() {
diff --git a/vlib/v/checker/tests/non_nil_array_with_nil_element_err.out b/vlib/v/checker/tests/non_nil_array_with_nil_element_err.out
new file mode 100644
index 00000000000000..20128caea0858a
--- /dev/null
+++ b/vlib/v/checker/tests/non_nil_array_with_nil_element_err.out
@@ -0,0 +1,8 @@
+vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv:1:23: error: invalid array element: expected `string`, not `voidptr`
+    1 | const spnames = ['f', unsafe { nil }]!
+      |                       ~~~~~~
+    2 | const spnames1 = [unsafe { nil }, 'f']!
+vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv:2:35: error: invalid array element: expected `voidptr`, not `string`
+    1 | const spnames = ['f', unsafe { nil }]!
+    2 | const spnames1 = [unsafe { nil }, 'f']!
+      |                                   ~~~
diff --git a/vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv b/vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv
new file mode 100644
index 00000000000000..67c7e1f5f867cc
--- /dev/null
+++ b/vlib/v/checker/tests/non_nil_array_with_nil_element_err.vv
@@ -0,0 +1,2 @@
+const spnames = ['f', unsafe { nil }]!
+const spnames1 = [unsafe { nil }, 'f']!
diff --git a/vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.out b/vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.out
index 37b765408b00b3..9bf7b9e622d90d 100644
--- a/vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.out
+++ b/vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.out
@@ -1,3 +1,10 @@
+vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.vv:15:2: error: cannot assign to field `name`: expected `string`, not `voidptr`
+   13 | 
+   14 | a := &Foo{
+   15 |     name: unsafe { nil }
+      |     ~~~~~~~~~~~~
+   16 |     bar: unsafe { nil }
+   17 |     name2: unsafe { nil }
 vlib/v/checker/tests/struct_field_assign_internal_types_nil_err.vv:15:8: error: cannot assign `nil` to struct field `name` with type `string`
    13 | 
    14 | a := &Foo{
diff --git a/vlib/v/tests/cast_fixed_array_to_ptr_ptr_test.v b/vlib/v/tests/cast_fixed_array_to_ptr_ptr_test.v
index 09ceec74c15a43..b0f5cee0a9f4bd 100644
--- a/vlib/v/tests/cast_fixed_array_to_ptr_ptr_test.v
+++ b/vlib/v/tests/cast_fixed_array_to_ptr_ptr_test.v
@@ -5,7 +5,7 @@ struct Foo {
 fn test_main() {
 	foo := Foo{
 		bar: unsafe {
-			&&char(['a', 'b', nil]!)
+			&&char([c'a', c'b', nil]!)
 		}
 	}
 	println(foo)