1 use crate::utils::span_lint;
2 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability};
3 use rustc_lint::{LateContext, LateLintPass};
4 use rustc_middle::ty::subst::Subst;
5 use rustc_middle::ty::{self, Ty};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// **What it does:** Detects giving a mutable reference to a function that only
10 /// requires an immutable reference.
12 /// **Why is this bad?** The immutable reference rules out all other references
13 /// to the value. Also the code misleads about the intent of the call site.
15 /// **Known problems:** None.
19 /// my_vec.push(&mut value)
21 pub UNNECESSARY_MUT_PASSED,
23 "an argument passed as a mutable reference although the callee only demands an immutable reference"
26 declare_lint_pass!(UnnecessaryMutPassed => [UNNECESSARY_MUT_PASSED]);
28 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
29 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
31 ExprKind::Call(ref fn_expr, ref arguments) => {
32 if let ExprKind::Path(ref path) = fn_expr.kind {
36 cx.tables.expr_ty(fn_expr),
37 &rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false)),
41 ExprKind::MethodCall(ref path, _, ref arguments) => {
42 let def_id = cx.tables.type_dependent_def_id(e.hir_id).unwrap();
43 let substs = cx.tables.node_substs(e.hir_id);
44 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
45 check_arguments(cx, arguments, method_type, &path.ident.as_str())
52 fn check_arguments<'a, 'tcx>(
53 cx: &LateContext<'a, 'tcx>,
54 arguments: &[Expr<'_>],
55 type_definition: Ty<'tcx>,
58 match type_definition.kind {
59 ty::FnDef(..) | ty::FnPtr(_) => {
60 let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
61 for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
62 match parameter.kind {
63 ty::Ref(_, _, Mutability::Not)
64 | ty::RawPtr(ty::TypeAndMut {
65 mutbl: Mutability::Not, ..
67 if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _) = argument.kind {
70 UNNECESSARY_MUT_PASSED,
72 &format!("The function/method `{}` doesn't need a mutable reference", name),