From 6aa81fa49ace053b11154656519fd1dcd7ab87c0 Mon Sep 17 00:00:00 2001
From: CreeperFace <165158232+dy-tea@users.noreply.github.com>
Date: Sat, 29 Nov 2025 06:55:12 +0000
Subject: [PATCH] parser: disallow untyped `chan` used as a fn parameter type
 (fix #25818) (#25854)

---
 vlib/v/parser/fn.v                            |  8 +++++++
 vlib/v/parser/messages.v                      |  5 +++++
 vlib/v/parser/parse_type.v                    | 21 +++++++++++++++++++
 .../tests/chan_no_type_array_fn_arg_err.out   |  3 +++
 .../tests/chan_no_type_array_fn_arg_err.vv    |  1 +
 vlib/v/parser/tests/chan_no_type_err.out      |  3 +++
 vlib/v/parser/tests/chan_no_type_err.vv       |  1 +
 .../parser/tests/chan_no_type_fn_arg_err.out  |  3 +++
 .../v/parser/tests/chan_no_type_fn_arg_err.vv |  1 +
 .../tests/chan_no_type_map_fn_arg_err.out     |  3 +++
 .../tests/chan_no_type_map_fn_arg_err.vv      |  1 +
 .../parser/tests/chan_no_type_option_err.out  |  3 +++
 .../v/parser/tests/chan_no_type_option_err.vv |  1 +
 vlib/v/parser/tests/chan_no_type_ref_err.out  |  3 +++
 vlib/v/parser/tests/chan_no_type_ref_err.vv   |  1 +
 15 files changed, 58 insertions(+)
 create mode 100644 vlib/v/parser/tests/chan_no_type_array_fn_arg_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_array_fn_arg_err.vv
 create mode 100644 vlib/v/parser/tests/chan_no_type_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_err.vv
 create mode 100644 vlib/v/parser/tests/chan_no_type_fn_arg_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_fn_arg_err.vv
 create mode 100644 vlib/v/parser/tests/chan_no_type_map_fn_arg_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_map_fn_arg_err.vv
 create mode 100644 vlib/v/parser/tests/chan_no_type_option_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_option_err.vv
 create mode 100644 vlib/v/parser/tests/chan_no_type_ref_err.out
 create mode 100644 vlib/v/parser/tests/chan_no_type_ref_err.vv

diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 44a7b2817..7de3ee48e 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -1047,6 +1047,10 @@ fn (mut p Parser) fn_params() ([]ast.Param, bool, bool, bool) {
 				// error is added in parse_type
 				return []ast.Param{}, false, false, false
 			}
+			if param_type == ast.chan_type {
+				p.chan_type_error()
+				return []ast.Param{}, false, false, false
+			}
 			if is_mut {
 				if !param_type.has_flag(.generic) {
 					if is_variadic {
@@ -1177,6 +1181,10 @@ fn (mut p Parser) fn_params() ([]ast.Param, bool, bool, bool) {
 				// error is added in parse_type
 				return []ast.Param{}, false, false, false
 			}
+			if typ == ast.chan_type {
+				p.chan_type_error()
+				return []ast.Param{}, false, false, false
+			}
 			if is_mut {
 				if !typ.has_flag(.generic) {
 					if is_variadic {
diff --git a/vlib/v/parser/messages.v b/vlib/v/parser/messages.v
index 8997f7188..6ea9b8b36 100644
--- a/vlib/v/parser/messages.v
+++ b/vlib/v/parser/messages.v
@@ -220,3 +220,8 @@ fn (mut p Parser) unexpected_with_pos(pos token.Pos, params ParamsForUnexpected)
 	}
 	return p.error_with_pos(msg, pos)
 }
+
+fn (mut p Parser) chan_type_error() {
+	p.error_with_pos('`chan` has no type specified. Use `chan Type` instead of `chan`',
+		p.prev_tok.pos())
+}
diff --git a/vlib/v/parser/parse_type.v b/vlib/v/parser/parse_type.v
index d54f725dd..13fb50023 100644
--- a/vlib/v/parser/parse_type.v
+++ b/vlib/v/parser/parse_type.v
@@ -124,6 +124,10 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 			// error is handled by parse_type
 			return 0
 		}
+		if elem_type == ast.chan_type {
+			p.chan_type_error()
+			return 0
+		}
 		// has been explicitly resolved, but size is 0
 		if fixed_size <= 0 && !size_unresolved {
 			p.error_with_pos('fixed size cannot be zero or negative', size_expr.pos())
@@ -142,6 +146,10 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 		// error is set in parse_type
 		return 0
 	}
+	if elem_type == ast.chan_type {
+		p.chan_type_error()
+		return 0
+	}
 	if elem_type.idx() == ast.thread_type_idx {
 		p.register_auto_import('sync.threads')
 	}
@@ -201,6 +209,10 @@ fn (mut p Parser) parse_map_type() ast.Type {
 		// error is reported in parse_type
 		return 0
 	}
+	if value_type == ast.chan_type {
+		p.chan_type_error()
+		return 0
+	}
 	if value_type.idx() == ast.void_type_idx {
 		p.error_with_pos('map value type is missing: use `map[KeyType]ValueType`', p.tok.pos())
 		return 0
@@ -293,6 +305,10 @@ fn (mut p Parser) parse_multi_return_type() ast.Type {
 		if mr_type.idx() == 0 {
 			break
 		}
+		if mr_type == ast.chan_type {
+			p.chan_type_error()
+			break
+		}
 		if mr_type.has_flag(.generic) {
 			has_generic = true
 		}
@@ -568,6 +584,11 @@ fn (mut p Parser) parse_type() ast.Type {
 			// error is set in parse_type
 			return 0
 		}
+		// !p.inside_receiver_param check can be removed once (ch chan) functions are removed
+		if typ == ast.chan_type && !p.inside_receiver_param {
+			p.chan_type_error()
+			return 0
+		}
 		if typ == ast.void_type {
 			p.error_with_pos('use `?` instead of `?void`', pos)
 			return 0
diff --git a/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.out b/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.out
new file mode 100644
index 000000000..308e98669
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_array_fn_arg_err.vv:1:24: error: `chan` has no type specified. Use `chan Type` instead of `chan`
+    1 | fn takes_array(chans []chan) {}
+      |                        ~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.vv b/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.vv
new file mode 100644
index 000000000..5efa99054
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_array_fn_arg_err.vv
@@ -0,0 +1 @@
+fn takes_array(chans []chan) {}
diff --git a/vlib/v/parser/tests/chan_no_type_err.out b/vlib/v/parser/tests/chan_no_type_err.out
new file mode 100644
index 000000000..3c68e8a27
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_err.vv:1:6: error: `chan` has no type specified. Use `chan Type{}` instead of `chan{}`
+    1 | a := chan{}
+      |      ~~~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_err.vv b/vlib/v/parser/tests/chan_no_type_err.vv
new file mode 100644
index 000000000..c956d27ab
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_err.vv
@@ -0,0 +1 @@
+a := chan{}
diff --git a/vlib/v/parser/tests/chan_no_type_fn_arg_err.out b/vlib/v/parser/tests/chan_no_type_fn_arg_err.out
new file mode 100644
index 000000000..89f0a4459
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_fn_arg_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_fn_arg_err.vv:1:12: error: `chan` has no type specified. Use `chan Type` instead of `chan`
+    1 | fn takes(c chan) {}
+      |            ~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_fn_arg_err.vv b/vlib/v/parser/tests/chan_no_type_fn_arg_err.vv
new file mode 100644
index 000000000..6eb50b3de
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_fn_arg_err.vv
@@ -0,0 +1 @@
+fn takes(c chan) {}
diff --git a/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.out b/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.out
new file mode 100644
index 000000000..6da48ed67
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_map_fn_arg_err.vv:1:31: error: `chan` has no type specified. Use `chan Type` instead of `chan`
+    1 | fn takes_map(chans map[string]chan) {}
+      |                               ~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.vv b/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.vv
new file mode 100644
index 000000000..0c1c7fe62
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_map_fn_arg_err.vv
@@ -0,0 +1 @@
+fn takes_map(chans map[string]chan) {}
diff --git a/vlib/v/parser/tests/chan_no_type_option_err.out b/vlib/v/parser/tests/chan_no_type_option_err.out
new file mode 100644
index 000000000..f4f213734
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_option_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_option_err.vv:1:17: error: `chan` has no type specified. Use `chan Type` instead of `chan`
+    1 | fn takes_opt(c ?chan) {}
+      |                 ~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_option_err.vv b/vlib/v/parser/tests/chan_no_type_option_err.vv
new file mode 100644
index 000000000..082efdef0
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_option_err.vv
@@ -0,0 +1 @@
+fn takes_opt(c ?chan) {}
diff --git a/vlib/v/parser/tests/chan_no_type_ref_err.out b/vlib/v/parser/tests/chan_no_type_ref_err.out
new file mode 100644
index 000000000..41f2ed4a6
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_ref_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/chan_no_type_ref_err.vv:1:17: error: `chan` has no type specified. Use `chan Type` instead of `chan`
+    1 | fn takes_ref(c &chan) {}
+      |                 ~~~~
diff --git a/vlib/v/parser/tests/chan_no_type_ref_err.vv b/vlib/v/parser/tests/chan_no_type_ref_err.vv
new file mode 100644
index 000000000..2077d6e81
--- /dev/null
+++ b/vlib/v/parser/tests/chan_no_type_ref_err.vv
@@ -0,0 +1 @@
+fn takes_ref(c &chan) {}
-- 
2.39.5