1 use if_chain::if_chain;
2 use rustc::lint::in_external_macro;
4 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
7 use crate::utils::{is_must_use_func_call, is_must_use_ty, span_help_and_lint};
10 /// **What it does:** Checks for `let _ = <expr>`
11 /// where expr is #[must_use]
13 /// **Why is this bad?** It's better to explicitly
14 /// handle the value of a #[must_use] expr
16 /// **Known problems:** None.
20 /// fn f() -> Result<u32, u32> {
25 /// // is_ok() is marked #[must_use]
26 /// let _ = f().is_ok();
28 pub LET_UNDERSCORE_MUST_USE,
30 "non-binding let on a `#[must_use]` expression"
33 declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE]);
35 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore {
36 fn check_stmt(&mut self, cx: &LateContext<'_, '_>, stmt: &Stmt<'_>) {
37 if in_external_macro(cx.tcx.sess, stmt.span) {
42 if let StmtKind::Local(ref local) = stmt.kind;
43 if let PatKind::Wild = local.pat.kind;
44 if let Some(ref init) = local.init;
46 if is_must_use_ty(cx, cx.tables.expr_ty(init)) {
49 LET_UNDERSCORE_MUST_USE,
51 "non-binding let on an expression with `#[must_use]` type",
52 "consider explicitly using expression value"
54 } else if is_must_use_func_call(cx, init) {
57 LET_UNDERSCORE_MUST_USE,
59 "non-binding let on a result of a `#[must_use]` function",
60 "consider explicitly using function result"