use crate::utils::span_lint; use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability}; use rustc_lint::{LateContext, LateLintPass}; use rustc_middle::ty::subst::Subst; use rustc_middle::ty::{self, Ty}; use rustc_session::{declare_lint_pass, declare_tool_lint}; declare_clippy_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:** /// ```ignore /// my_vec.push(&mut value) /// ``` pub UNNECESSARY_MUT_PASSED, style, "an argument passed as a mutable reference although the callee only demands an immutable reference" } declare_lint_pass!(UnnecessaryMutPassed => [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.kind { ExprKind::Call(ref fn_expr, ref arguments) => { if let ExprKind::Path(ref path) = fn_expr.kind { check_arguments( cx, arguments, cx.tables.expr_ty(fn_expr), &rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false)), ); } }, ExprKind::MethodCall(ref path, _, ref arguments) => { let def_id = cx.tables.type_dependent_def_id(e.hir_id).unwrap(); 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.ident.as_str()) }, _ => (), } } } fn check_arguments<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, arguments: &[Expr<'_>], type_definition: Ty<'tcx>, name: &str, ) { match type_definition.kind { ty::FnDef(..) | ty::FnPtr(_) => { let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs(); for (argument, parameter) in arguments.iter().zip(parameters.iter()) { match parameter.kind { ty::Ref(_, _, Mutability::Not) | ty::RawPtr(ty::TypeAndMut { mutbl: Mutability::Not, .. }) => { if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _) = argument.kind { span_lint( cx, UNNECESSARY_MUT_PASSED, argument.span, &format!("The function/method `{}` doesn't need a mutable reference", name), ); } }, _ => (), } } }, _ => (), } }