From 66bc5417cd95a5597f3242979dfb702e2f5f90b8 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 26 Feb 2026 10:19:17 +0300
Subject: [PATCH] parser: fix function body `{` error message is not correct
 (fixes #16133)

---
 vlib/v/parser/fn.v                                         | 7 ++++++-
 .../parser/tests/fn_decl_invalid_body_opener_lsbr_err.out  | 3 +++
 .../v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv | 3 +++
 3 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.out
 create mode 100644 vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv

diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 55bc44a0d..5553b3f45 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -760,7 +760,12 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	mut return_type := ast.void_type
 	// don't confuse token on the next line: fn decl, [attribute]
 	same_line := p.tok.line_nr == p.prev_tok.line_nr
-	if (p.tok.kind.is_start_of_type() && (same_line || p.tok.kind != .lsbr))
+	// `fn foo()[` is usually a mistaken body opener; report it as such
+	// instead of trying to parse `[` as a fixed array return type.
+	invalid_body_opener := same_line && p.tok.kind == .lsbr && p.peek_tok.line_nr > p.tok.line_nr
+	if invalid_body_opener {
+		p.unexpected(got: '${p.tok} after function signature', expecting: '`{`')
+	} else if (p.tok.kind.is_start_of_type() && (same_line || p.tok.kind != .lsbr))
 		|| (same_line && p.tok.kind == .key_fn) {
 		// Disallow [T] as return type
 		if p.tok.kind == .lsbr && p.peek_tok.kind == .name && p.peek_tok.lit.len == 1
diff --git a/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.out b/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.out
new file mode 100644
index 000000000..c037213e9
--- /dev/null
+++ b/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.out
@@ -0,0 +1,3 @@
+vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv:1:9: error: unexpected token `[` after function signature, expecting `{`
+    1 | fn foo()[
+      |         ^
diff --git a/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv b/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv
new file mode 100644
index 000000000..2c86f3d3f
--- /dev/null
+++ b/vlib/v/parser/tests/fn_decl_invalid_body_opener_lsbr_err.vv
@@ -0,0 +1,3 @@
+fn foo()[
+	println('')
+]
-- 
2.39.5