2 use rustc::{declare_lint, lint_array};
3 use rustc::ty::{self, Ty};
4 use rustc::ty::subst::Subst;
6 use crate::utils::span_lint;
8 /// **What it does:** Detects giving a mutable reference to a function that only
9 /// requires an immutable reference.
11 /// **Why is this bad?** The immutable reference rules out all other references
12 /// to the value. Also the code misleads about the intent of the call site.
14 /// **Known problems:** None.
18 /// my_vec.push(&mut value)
20 declare_clippy_lint! {
21 pub UNNECESSARY_MUT_PASSED,
23 "an argument passed as a mutable reference although the callee only demands an \
28 #[derive(Copy, Clone)]
29 pub struct UnnecessaryMutPassed;
31 impl LintPass for UnnecessaryMutPassed {
32 fn get_lints(&self) -> LintArray {
33 lint_array!(UNNECESSARY_MUT_PASSED)
37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
38 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
40 ExprKind::Call(ref fn_expr, ref arguments) => if let ExprKind::Path(ref path) = fn_expr.node {
44 cx.tables.expr_ty(fn_expr),
45 &print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
48 ExprKind::MethodCall(ref path, _, ref arguments) => {
49 let def_id = cx.tables.type_dependent_defs()[e.hir_id].def_id();
50 let substs = cx.tables.node_substs(e.hir_id);
51 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
52 check_arguments(cx, arguments, method_type, &path.ident.as_str())
59 fn check_arguments<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arguments: &[Expr], type_definition: Ty<'tcx>, name: &str) {
60 match type_definition.sty {
61 ty::TyFnDef(..) | ty::TyFnPtr(_) => {
62 let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
63 for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
70 ty::TyRawPtr(ty::TypeAndMut {
73 }) => if let ExprKind::AddrOf(MutMutable, _) = argument.node {
76 UNNECESSARY_MUT_PASSED,
78 &format!("The function/method `{}` doesn't need a mutable reference", name),