From 00b9f0d76cc0e621c7dc3343cd3e9b047531191a Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 11 Mar 2026 16:19:02 +0300
Subject: [PATCH] checker: builder error "This should never happen" (fixes
 #12434)

---
 vlib/v/ast/cflags.v                              | 3 +++
 vlib/v/ast/cflags_test.v                         | 1 +
 vlib/v/checker/tests/hash_flag_backticks_err.out | 5 +++++
 vlib/v/checker/tests/hash_flag_backticks_err.vv  | 3 +++
 4 files changed, 12 insertions(+)
 create mode 100644 vlib/v/checker/tests/hash_flag_backticks_err.out
 create mode 100644 vlib/v/checker/tests/hash_flag_backticks_err.vv

diff --git a/vlib/v/ast/cflags.v b/vlib/v/ast/cflags.v
index 413b7ec7c..fe7a65c85 100644
--- a/vlib/v/ast/cflags.v
+++ b/vlib/v/ast/cflags.v
@@ -24,6 +24,9 @@ pub fn (mut t Table) parse_cflag(cflg string, mod string, ctimedefines []string)
 	if flag == '' {
 		return error('flag is empty')
 	}
+	if flag.contains('`') {
+		return error('bad #flag `${flag_orig}`: shell command substitution with backticks is not supported; use #pkgconfig or explicit flags instead')
+	}
 	mut fos := ''
 	mut allowed_os_overrides := []string{}
 	allowed_os_overrides << valid_comptime_not_user_defined
diff --git a/vlib/v/ast/cflags_test.v b/vlib/v/ast/cflags_test.v
index 1fa98de9a..cc80d4330 100644
--- a/vlib/v/ast/cflags_test.v
+++ b/vlib/v/ast/cflags_test.v
@@ -52,6 +52,7 @@ fn test_parse_invalid_cflags() {
 	assert_parse_invalid_flag(mut t, 'windows -l')
 	assert_parse_invalid_flag(mut t, '-I')
 	assert_parse_invalid_flag(mut t, '-L')
+	assert_parse_invalid_flag(mut t, 'darwin `sdl2-config --cflags --libs` -lSDL2')
 	// OS/compiler name only is not allowed
 	assert_parse_invalid_flag(mut t, 'darwin')
 	assert_parse_invalid_flag(mut t, 'freebsd')
diff --git a/vlib/v/checker/tests/hash_flag_backticks_err.out b/vlib/v/checker/tests/hash_flag_backticks_err.out
new file mode 100644
index 000000000..64ba4d655
--- /dev/null
+++ b/vlib/v/checker/tests/hash_flag_backticks_err.out
@@ -0,0 +1,5 @@
+vlib/v/checker/tests/hash_flag_backticks_err.vv:1:1: error: bad #flag `darwin `sdl2-config --cflags --libs` -lSDL2`: shell command substitution with backticks is not supported; use #pkgconfig or explicit flags instead
+    1 | #flag darwin `sdl2-config --cflags --libs` -lSDL2
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 | 
+    3 | fn main() {}
diff --git a/vlib/v/checker/tests/hash_flag_backticks_err.vv b/vlib/v/checker/tests/hash_flag_backticks_err.vv
new file mode 100644
index 000000000..3842e58ca
--- /dev/null
+++ b/vlib/v/checker/tests/hash_flag_backticks_err.vv
@@ -0,0 +1,3 @@
+#flag darwin `sdl2-config --cflags --libs` -lSDL2
+
+fn main() {}
-- 
2.39.5