Include --check-cfg=cfg(kani) in the rust flags to avoid a warning about an unknown cfg.

kani-driver/src/call_single_file.rs

@@ -133,6 +133,7 @@ impl KaniSession {
                 "panic_abort_tests=yes",
                 "-Z",
                 "mir-enable-passes=-RemoveStorageMarkers",
+                "--check-cfg=cfg(kani)",
             ]
             .map(OsString::from),
         );

tests/cargo-kani/unexpected_cfgs/Cargo.toml

@@ -0,0 +1,9 @@
+# Copyright Kani Contributors
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+
+[package]
+name = "unexpected_cfgs"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

tests/cargo-kani/unexpected_cfgs/expected

@@ -0,0 +1 @@
+VERIFICATION:- SUCCESSFUL

tests/cargo-kani/unexpected_cfgs/src/main.rs

@@ -0,0 +1,19 @@
+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// This test checks that the `unexpected_cfgs` lint (enabled by default as of
+// the 2024-05-05 toolchain) does not cause `cargo kani` to emit warnings when
+// the code has `#[cfg(kani)]`. Kani avoids the warning by adding
+// `--check-cfg=cfg(kani)` to the rust flags.
+
+#![deny(unexpected_cfgs)]
+
+fn main() {}
+
+#[cfg(kani)]
+mod kani_checks {
+    #[kani::proof]
+    fn check_unexpected_cfg() {
+        assert_eq!(1, 1);
+    }
+}