use rustc::lint::*; use rustc::ty::{self, Ty}; use rustc::ty::subst::Subst; use rustc::hir::*; use utils::span_lint; /// **What it does:** Detects giving a mutable reference to a function that only /// requires an immutable reference. /// /// **Why is this bad?** The immutable reference rules out all other references /// to the value. Also the code misleads about the intent of the call site. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// my_vec.push(&mut value) /// ``` declare_clippy_lint! { pub UNNECESSARY_MUT_PASSED, style, "an argument passed as a mutable reference although the callee only demands an \ immutable reference" } #[derive(Copy, Clone)] pub struct UnnecessaryMutPassed; impl LintPass for UnnecessaryMutPassed { fn get_lints(&self) -> LintArray { lint_array!(UNNECESSARY_MUT_PASSED) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) { match e.node { ExprCall(ref fn_expr, ref arguments) => if let ExprPath(ref path) = fn_expr.node { check_arguments( cx, arguments, cx.tables.expr_ty(fn_expr), &print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)), ); }, ExprMethodCall(ref path, _, ref arguments) => { let def_id = cx.tables.type_dependent_defs()[e.hir_id].def_id(); let substs = cx.tables.node_substs(e.hir_id); let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs); check_arguments(cx, arguments, method_type, &path.name.as_str()) }, _ => (), } } } fn check_arguments<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arguments: &[Expr], type_definition: Ty<'tcx>, name: &str) { match type_definition.sty { ty::TyFnDef(..) | ty::TyFnPtr(_) => { let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs(); for (argument, parameter) in arguments.iter().zip(parameters.iter()) { match parameter.sty { ty::TyRef( _, _, MutImmutable, ) | ty::TyRawPtr(ty::TypeAndMut { mutbl: MutImmutable, .. }) => if let ExprAddrOf(MutMutable, _) = argument.node { span_lint( cx, UNNECESSARY_MUT_PASSED, argument.span, &format!("The function/method `{}` doesn't need a mutable reference", name), ); }, _ => (), } } }, _ => (), } }