2 use rustc::ty::{self, Ty};
3 use rustc::ty::subst::Subst;
7 /// **What it does:** Detects giving a mutable reference to a function that only
8 /// requires an immutable reference.
10 /// **Why is this bad?** The immutable reference rules out all other references
11 /// to the value. Also the code misleads about the intent of the call site.
13 /// **Known problems:** None.
17 /// my_vec.push(&mut value)
20 pub UNNECESSARY_MUT_PASSED,
22 "an argument passed as a mutable reference although the callee only demands an \
28 pub struct UnnecessaryMutPassed;
30 impl LintPass for UnnecessaryMutPassed {
31 fn get_lints(&self) -> LintArray {
32 lint_array!(UNNECESSARY_MUT_PASSED)
36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
37 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
39 ExprCall(ref fn_expr, ref arguments) => {
40 if let ExprPath(ref path) = fn_expr.node {
43 cx.tables.expr_ty(fn_expr),
44 &print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)));
47 ExprMethodCall(ref path, _, ref arguments) => {
48 let def_id = cx.tables.type_dependent_defs[&e.id].def_id();
49 let substs = cx.tables.node_substs(e.id);
50 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
51 check_arguments(cx, arguments, method_type, &path.name.as_str())
58 fn check_arguments<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arguments: &[Expr], type_definition: Ty<'tcx>, name: &str) {
59 match type_definition.sty {
60 ty::TyFnDef(..) | ty::TyFnPtr(_) => {
61 let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
62 for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
64 ty::TyRef(_, ty::TypeAndMut { mutbl: MutImmutable, .. }) |
65 ty::TyRawPtr(ty::TypeAndMut { mutbl: MutImmutable, .. }) => {
66 if let ExprAddrOf(MutMutable, _) = argument.node {
68 UNNECESSARY_MUT_PASSED,
70 &format!("The function/method `{}` doesn't need a mutable reference", name));