From c8623943584a34090eb22bb88886b118ba21df8b Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Fri, 18 Aug 2023 01:41:02 +0530
Subject: [PATCH] parser: disallow an empty `chan` type (#19167)

---
 vlib/v/parser/parser.v                            | 4 ++++
 vlib/v/parser/tests/no_chan_type_provided_err.out | 3 +++
 vlib/v/parser/tests/no_chan_type_provided_err.vv  | 1 +
 3 files changed, 8 insertions(+)
 create mode 100644 vlib/v/parser/tests/no_chan_type_provided_err.out
 create mode 100644 vlib/v/parser/tests/no_chan_type_provided_err.vv

diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index f14cda6666ad47..5c432f0a3dcea4 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -2537,6 +2537,10 @@ fn (mut p Parser) name_expr() ast.Expr {
 			last_pos = p.tok.pos()
 			p.check(.rcbr)
 		}
+		if chan_type == ast.chan_type {
+			p.error_with_pos('`chan` has no type specified. Use `chan Type{}` instead of `chan{}`',
+				first_pos.extend(last_pos))
+		}
 		return ast.ChanInit{
 			pos: first_pos.extend(last_pos)
 			elem_type_pos: elem_type_pos
diff --git a/vlib/v/parser/tests/no_chan_type_provided_err.out b/vlib/v/parser/tests/no_chan_type_provided_err.out
new file mode 100644
index 00000000000000..2a5049319b6386
--- /dev/null
+++ b/vlib/v/parser/tests/no_chan_type_provided_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/no_chan_type_provided_err.vv:1:5: error: `chan` has no type specified. Use `chan Type{}` instead of `chan{}`
+    1 | _ = chan{}
+      |     ~~~~~~
diff --git a/vlib/v/parser/tests/no_chan_type_provided_err.vv b/vlib/v/parser/tests/no_chan_type_provided_err.vv
new file mode 100644
index 00000000000000..83bf66e7a00e8a
--- /dev/null
+++ b/vlib/v/parser/tests/no_chan_type_provided_err.vv
@@ -0,0 +1 @@
+_ = chan{}