From 3be78d6777caee18a3ba061f19c5f88a557d7882 Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Fri, 12 Mar 2021 12:17:37 +0000
Subject: [PATCH] parser: require anonymous fn to use `_` for unused parameters
 (#9262)

Fixes a C error with gcc.
---
 vlib/v/parser/fn.v                        | 3 +++
 vlib/v/parser/tests/anon_unused_param.out | 4 ++++
 vlib/v/parser/tests/anon_unused_param.vv  | 2 ++
 3 files changed, 9 insertions(+)
 create mode 100644 vlib/v/parser/tests/anon_unused_param.out
 create mode 100644 vlib/v/parser/tests/anon_unused_param.vv

diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 133049e95..e8dcfea53 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -544,6 +544,9 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 	// TODO generics
 	args, _, is_variadic := p.fn_args()
 	for arg in args {
+		if arg.name.len == 0 {
+			p.error_with_pos('use `_` to name an unused parameter', arg.pos)
+		}
 		p.scope.register(ast.Var{
 			name: arg.name
 			typ: arg.typ
diff --git a/vlib/v/parser/tests/anon_unused_param.out b/vlib/v/parser/tests/anon_unused_param.out
new file mode 100644
index 000000000..a12769b30
--- /dev/null
+++ b/vlib/v/parser/tests/anon_unused_param.out
@@ -0,0 +1,4 @@
+vlib/v/parser/tests/anon_unused_param.vv:1:9: error: use `_` to name an unused parameter
+    1 | _ = fn (int){}
+      |         ~~~
+    2 |
diff --git a/vlib/v/parser/tests/anon_unused_param.vv b/vlib/v/parser/tests/anon_unused_param.vv
new file mode 100644
index 000000000..c285cea3c
--- /dev/null
+++ b/vlib/v/parser/tests/anon_unused_param.vv
@@ -0,0 +1,2 @@
+_ = fn (int){}
+
-- 
2.39.5