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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::macros::{find_assert_args, find_assert_eq_args, root_macro_call_first_node, PanicExpn};
use clippy_utils::{is_in_cfg_test, is_in_test_function};
use rustc_hir::Expr;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks assertions without a custom panic message.
///
/// ### Why is this bad?
/// Without a good custom message, it'd be hard to understand what went wrong when the assertion fails.
/// A good custom message should be more about why the failure of the assertion is problematic
/// and not what is failed because the assertion already conveys that.
///
/// Although the same reasoning applies to testing functions, this lint ignores them as they would be too noisy.
/// Also, in most cases understanding the test failure would be easier
/// compared to understanding a complex invariant distributed around the codebase.
///
/// ### Known problems
/// This lint cannot check the quality of the custom panic messages.
/// Hence, you can suppress this lint simply by adding placeholder messages
/// like "assertion failed". However, we recommend coming up with good messages
/// that provide useful information instead of placeholder messages that
/// don't provide any extra information.
///
/// ### Example
/// ```no_run
/// # struct Service { ready: bool }
/// fn call(service: Service) {
/// assert!(service.ready);
/// }
/// ```
/// Use instead:
/// ```no_run
/// # struct Service { ready: bool }
/// fn call(service: Service) {
/// assert!(service.ready, "`service.poll_ready()` must be called first to ensure that service is ready to receive requests");
/// }
/// ```
#[clippy::version = "1.70.0"]
pub MISSING_ASSERT_MESSAGE,
restriction,
"checks assertions without a custom panic message"
}
declare_lint_pass!(MissingAssertMessage => [MISSING_ASSERT_MESSAGE]);
impl<'tcx> LateLintPass<'tcx> for MissingAssertMessage {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
let Some(macro_call) = root_macro_call_first_node(cx, expr) else {
return;
};
let single_argument = match cx.tcx.get_diagnostic_name(macro_call.def_id) {
Some(sym::assert_macro | sym::debug_assert_macro) => true,
Some(
sym::assert_eq_macro | sym::assert_ne_macro | sym::debug_assert_eq_macro | sym::debug_assert_ne_macro,
) => false,
_ => return,
};
// This lint would be very noisy in tests, so just ignore if we're in test context
if is_in_test_function(cx.tcx, expr.hir_id) || is_in_cfg_test(cx.tcx, expr.hir_id) {
return;
}
let panic_expn = if single_argument {
let Some((_, panic_expn)) = find_assert_args(cx, expr, macro_call.expn) else {
return;
};
panic_expn
} else {
let Some((_, _, panic_expn)) = find_assert_eq_args(cx, expr, macro_call.expn) else {
return;
};
panic_expn
};
if let PanicExpn::Empty = panic_expn {
span_lint_and_help(
cx,
MISSING_ASSERT_MESSAGE,
macro_call.span,
"assert without any message",
None,
"consider describing why the failing assert is problematic",
);
}
}
}
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