From ada32cd4102166d457e1ab8437e93527ed5a5ee9 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 26 Feb 2026 08:38:32 +0300
Subject: [PATCH] checker: fix byte/u8 array param type checking and var-fn
 name clash (fixes #26492)

---
 .../tests/use_byte_instead_of_u8_array_param_err.out      | 5 +++++
 .../tests/use_byte_instead_of_u8_array_param_err.vv       | 3 +++
 .../tests/use_byte_instead_of_u8_array_type_err.out       | 6 ++++++
 .../tests/use_byte_instead_of_u8_array_type_err.vv        | 5 +++++
 vlib/v/parser/parse_type.v                                | 8 ++++++++
 vlib/v/tests/clash_var_fn_name_test.v                     | 2 +-
 6 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.out
 create mode 100644 vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.vv
 create mode 100644 vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.out
 create mode 100644 vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.vv

diff --git a/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.out b/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.out
new file mode 100644
index 000000000..ca0d564ae
--- /dev/null
+++ b/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.out
@@ -0,0 +1,5 @@
+vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.vv:1:20: error: byte is deprecated, use u8 instead
+    1 | fn takes_bytes(_ []byte) {}
+      |                    ~~~~
+    2 |
+    3 | fn main() {}
diff --git a/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.vv b/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.vv
new file mode 100644
index 000000000..3d2ac5781
--- /dev/null
+++ b/vlib/v/checker/tests/use_byte_instead_of_u8_array_param_err.vv
@@ -0,0 +1,3 @@
+fn takes_bytes(_ []byte) {}
+
+fn main() {}
diff --git a/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.out b/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.out
new file mode 100644
index 000000000..c9a8fa1c5
--- /dev/null
+++ b/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.vv:2:8: error: byte is deprecated, use u8 instead
+    1 | struct Test {
+    2 |     bar []byte
+      |           ~~~~
+    3 | }
+    4 |
diff --git a/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.vv b/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.vv
new file mode 100644
index 000000000..dc5e700cf
--- /dev/null
+++ b/vlib/v/checker/tests/use_byte_instead_of_u8_array_type_err.vv
@@ -0,0 +1,5 @@
+struct Test {
+	bar []byte
+}
+
+fn main() {}
diff --git a/vlib/v/parser/parse_type.v b/vlib/v/parser/parse_type.v
index ffcfa9708..62bdb6d84 100644
--- a/vlib/v/parser/parse_type.v
+++ b/vlib/v/parser/parse_type.v
@@ -119,6 +119,10 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 		defer {
 			p.fixed_array_dim--
 		}
+		elem_type_pos := p.tok.pos()
+		if p.tok.kind == .name && p.tok.lit == 'byte' {
+			p.error_with_pos('byte is deprecated, use u8 instead', elem_type_pos)
+		}
 		elem_type := p.parse_type()
 		if elem_type.idx() == 0 {
 			// error is handled by parse_type
@@ -141,6 +145,10 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 	}
 	// array
 	p.check(.rsbr)
+	elem_type_pos := p.tok.pos()
+	if p.tok.kind == .name && p.tok.lit == 'byte' {
+		p.error_with_pos('byte is deprecated, use u8 instead', elem_type_pos)
+	}
 	elem_type := p.parse_type()
 	if elem_type.idx() == 0 {
 		// error is set in parse_type
diff --git a/vlib/v/tests/clash_var_fn_name_test.v b/vlib/v/tests/clash_var_fn_name_test.v
index 0b78d32b0..52877f69e 100644
--- a/vlib/v/tests/clash_var_fn_name_test.v
+++ b/vlib/v/tests/clash_var_fn_name_test.v
@@ -1,4 +1,4 @@
-fn func(rune_bytes []byte) string {
+fn func(rune_bytes []u8) string {
 	return rune_bytes.str()
 }
 
-- 
2.39.5