src/tools/clippy/clippy_lints/src/methods/unnecessary_to_owned.rs

   1 use super::implicit_clone::is_clone_like;
   2 use super::unnecessary_iter_cloned::{self, is_into_iter};
   3 use crate::rustc_middle::ty::Subst;
   4 use clippy_utils::diagnostics::span_lint_and_sugg;
   5 use clippy_utils::source::snippet_opt;
   6 use clippy_utils::ty::{get_associated_type, get_iterator_item_ty, implements_trait, is_copy, peel_mid_ty_refs};
   7 use clippy_utils::visitors::find_all_ret_expressions;
   8 use clippy_utils::{fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item, return_ty};
   9 use clippy_utils::{meets_msrv, msrvs};
  10 use rustc_errors::Applicability;
  11 use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind, ItemKind, Node};
  12 use rustc_infer::infer::TyCtxtInferExt;
  13 use rustc_lint::LateContext;
  14 use rustc_middle::mir::Mutability;
  15 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref};
  16 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  17 use rustc_middle::ty::EarlyBinder;
  18 use rustc_middle::ty::{self, ParamTy, PredicateKind, ProjectionPredicate, TraitPredicate, Ty};
  19 use rustc_semver::RustcVersion;
  20 use rustc_span::{sym, Symbol};
  21 use rustc_trait_selection::traits::{query::evaluate_obligation::InferCtxtExt as _, Obligation, ObligationCause};
  22 use rustc_typeck::check::{FnCtxt, Inherited};
  23 use std::cmp::max;
  24
  25 use super::UNNECESSARY_TO_OWNED;
  26
  27 pub fn check<'tcx>(
  28     cx: &LateContext<'tcx>,
  29     expr: &'tcx Expr<'tcx>,
  30     method_name: Symbol,
  31     receiver: &'tcx Expr<'_>,
  32     args: &'tcx [Expr<'_>],
  33     msrv: Option<RustcVersion>,
  34 ) {
  35     if_chain! {
  36         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  37         if args.is_empty();
  38         then {
  39             if is_cloned_or_copied(cx, method_name, method_def_id) {
  40                 unnecessary_iter_cloned::check(cx, expr, method_name, receiver);
  41             } else if is_to_owned_like(cx, expr, method_name, method_def_id) {
  42                 // At this point, we know the call is of a `to_owned`-like function. The functions
  43                 // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
  44                 // based on its context, that is, whether it is a referent in an `AddrOf` expression, an
  45                 // argument in a `into_iter` call, or an argument in the call of some other function.
  46                 if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
  47                     return;
  48                 }
  49                 if check_into_iter_call_arg(cx, expr, method_name, receiver, msrv) {
  50                     return;
  51                 }
  52                 check_other_call_arg(cx, expr, method_name, receiver);
  53             }
  54         }
  55     }
  56 }
  57
  58 /// Checks whether `expr` is a referent in an `AddrOf` expression and, if so, determines whether its
  59 /// call of a `to_owned`-like function is unnecessary.
  60 #[allow(clippy::too_many_lines)]
  61 fn check_addr_of_expr(
  62     cx: &LateContext<'_>,
  63     expr: &Expr<'_>,
  64     method_name: Symbol,
  65     method_def_id: DefId,
  66     receiver: &Expr<'_>,
  67 ) -> bool {
  68     if_chain! {
  69         if let Some(parent) = get_parent_expr(cx, expr);
  70         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind;
  71         let adjustments = cx.typeck_results().expr_adjustments(parent).iter().collect::<Vec<_>>();
  72         if let
  73             // For matching uses of `Cow::from`
  74             [
  75                 Adjustment {
  76                     kind: Adjust::Deref(None),
  77                     target: referent_ty,
  78                 },
  79                 Adjustment {
  80                     kind: Adjust::Borrow(_),
  81                     target: target_ty,
  82                 },
  83             ]
  84             // For matching uses of arrays
  85             | [
  86                 Adjustment {
  87                     kind: Adjust::Deref(None),
  88                     target: referent_ty,
  89                 },
  90                 Adjustment {
  91                     kind: Adjust::Borrow(_),
  92                     ..
  93                 },
  94                 Adjustment {
  95                     kind: Adjust::Pointer(_),
  96                     target: target_ty,
  97                 },
  98             ]
  99             // For matching everything else
 100             | [
 101                 Adjustment {
 102                     kind: Adjust::Deref(None),
 103                     target: referent_ty,
 104                 },
 105                 Adjustment {
 106                     kind: Adjust::Deref(Some(OverloadedDeref { .. })),
 107                     ..
 108                 },
 109                 Adjustment {
 110                     kind: Adjust::Borrow(_),
 111                     target: target_ty,
 112                 },
 113             ] = adjustments[..];
 114         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 115         let (target_ty, n_target_refs) = peel_mid_ty_refs(*target_ty);
 116         let (receiver_ty, n_receiver_refs) = peel_mid_ty_refs(receiver_ty);
 117         // Only flag cases satisfying at least one of the following three conditions:
 118         // * the referent and receiver types are distinct
 119         // * the referent/receiver type is a copyable array
 120         // * the method is `Cow::into_owned`
 121         // This restriction is to ensure there is no overlap between `redundant_clone` and this
 122         // lint. It also avoids the following false positive:
 123         //  https://github.com/rust-lang/rust-clippy/issues/8759
 124         //   Arrays are a bit of a corner case. Non-copyable arrays are handled by
 125         // `redundant_clone`, but copyable arrays are not.
 126         if *referent_ty != receiver_ty
 127             || (matches!(referent_ty.kind(), ty::Array(..)) && is_copy(cx, *referent_ty))
 128             || is_cow_into_owned(cx, method_name, method_def_id);
 129         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 130         then {
 131             if receiver_ty == target_ty && n_target_refs >= n_receiver_refs {
 132                 span_lint_and_sugg(
 133                     cx,
 134                     UNNECESSARY_TO_OWNED,
 135                     parent.span,
 136                     &format!("unnecessary use of `{}`", method_name),
 137                     "use",
 138                     format!(
 139                         "{:&>width$}{}",
 140                         "",
 141                         receiver_snippet,
 142                         width = n_target_refs - n_receiver_refs
 143                     ),
 144                     Applicability::MachineApplicable,
 145                 );
 146                 return true;
 147             }
 148             if_chain! {
 149                 if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 150                 if implements_trait(cx, receiver_ty, deref_trait_id, &[]);
 151                 if get_associated_type(cx, receiver_ty, deref_trait_id, "Target") == Some(target_ty);
 152                 then {
 153                     if n_receiver_refs > 0 {
 154                         span_lint_and_sugg(
 155                             cx,
 156                             UNNECESSARY_TO_OWNED,
 157                             parent.span,
 158                             &format!("unnecessary use of `{}`", method_name),
 159                             "use",
 160                             receiver_snippet,
 161                             Applicability::MachineApplicable,
 162                         );
 163                     } else {
 164                         span_lint_and_sugg(
 165                             cx,
 166                             UNNECESSARY_TO_OWNED,
 167                             expr.span.with_lo(receiver.span.hi()),
 168                             &format!("unnecessary use of `{}`", method_name),
 169                             "remove this",
 170                             String::new(),
 171                             Applicability::MachineApplicable,
 172                         );
 173                     }
 174                     return true;
 175                 }
 176             }
 177             if_chain! {
 178                 if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 179                 if implements_trait(cx, receiver_ty, as_ref_trait_id, &[GenericArg::from(target_ty)]);
 180                 then {
 181                     span_lint_and_sugg(
 182                         cx,
 183                         UNNECESSARY_TO_OWNED,
 184                         parent.span,
 185                         &format!("unnecessary use of `{}`", method_name),
 186                         "use",
 187                         format!("{}.as_ref()", receiver_snippet),
 188                         Applicability::MachineApplicable,
 189                     );
 190                     return true;
 191                 }
 192             }
 193         }
 194     }
 195     false
 196 }
 197
 198 /// Checks whether `expr` is an argument in an `into_iter` call and, if so, determines whether its
 199 /// call of a `to_owned`-like function is unnecessary.
 200 fn check_into_iter_call_arg(
 201     cx: &LateContext<'_>,
 202     expr: &Expr<'_>,
 203     method_name: Symbol,
 204     receiver: &Expr<'_>,
 205     msrv: Option<RustcVersion>,
 206 ) -> bool {
 207     if_chain! {
 208         if let Some(parent) = get_parent_expr(cx, expr);
 209         if let Some(callee_def_id) = fn_def_id(cx, parent);
 210         if is_into_iter(cx, callee_def_id);
 211         if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
 212         let parent_ty = cx.typeck_results().expr_ty(parent);
 213         if implements_trait(cx, parent_ty, iterator_trait_id, &[]);
 214         if let Some(item_ty) = get_iterator_item_ty(cx, parent_ty);
 215         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 216         then {
 217             if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver, true) {
 218                 return true;
 219             }
 220             let cloned_or_copied = if is_copy(cx, item_ty) && meets_msrv(msrv, msrvs::ITERATOR_COPIED) {
 221                 "copied"
 222             } else {
 223                 "cloned"
 224             };
 225             // The next suggestion may be incorrect because the removal of the `to_owned`-like
 226             // function could cause the iterator to hold a reference to a resource that is used
 227             // mutably. See https://github.com/rust-lang/rust-clippy/issues/8148.
 228             span_lint_and_sugg(
 229                 cx,
 230                 UNNECESSARY_TO_OWNED,
 231                 parent.span,
 232                 &format!("unnecessary use of `{}`", method_name),
 233                 "use",
 234                 format!("{}.iter().{}()", receiver_snippet, cloned_or_copied),
 235                 Applicability::MaybeIncorrect,
 236             );
 237             return true;
 238         }
 239     }
 240     false
 241 }
 242
 243 /// Checks whether `expr` is an argument in a function call and, if so, determines whether its call
 244 /// of a `to_owned`-like function is unnecessary.
 245 fn check_other_call_arg<'tcx>(
 246     cx: &LateContext<'tcx>,
 247     expr: &'tcx Expr<'tcx>,
 248     method_name: Symbol,
 249     receiver: &'tcx Expr<'tcx>,
 250 ) -> bool {
 251     if_chain! {
 252         if let Some((maybe_call, maybe_arg)) = skip_addr_of_ancestors(cx, expr);
 253         if let Some((callee_def_id, _, recv, call_args)) = get_callee_substs_and_args(cx, maybe_call);
 254         let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 255         if let Some(i) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == maybe_arg.hir_id);
 256         if let Some(input) = fn_sig.inputs().get(i);
 257         let (input, n_refs) = peel_mid_ty_refs(*input);
 258         if let (trait_predicates, _) = get_input_traits_and_projections(cx, callee_def_id, input);
 259         if let Some(sized_def_id) = cx.tcx.lang_items().sized_trait();
 260         if let [trait_predicate] = trait_predicates
 261             .iter()
 262             .filter(|trait_predicate| trait_predicate.def_id() != sized_def_id)
 263             .collect::<Vec<_>>()[..];
 264         if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 265         if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 266         if trait_predicate.def_id() == deref_trait_id || trait_predicate.def_id() == as_ref_trait_id;
 267         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 268         if can_change_type(cx, maybe_arg, receiver_ty);
 269         // We can't add an `&` when the trait is `Deref` because `Target = &T` won't match
 270         // `Target = T`.
 271         if n_refs > 0 || is_copy(cx, receiver_ty) || trait_predicate.def_id() != deref_trait_id;
 272         let n_refs = max(n_refs, if is_copy(cx, receiver_ty) { 0 } else { 1 });
 273         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 274         then {
 275             span_lint_and_sugg(
 276                 cx,
 277                 UNNECESSARY_TO_OWNED,
 278                 maybe_arg.span,
 279                 &format!("unnecessary use of `{}`", method_name),
 280                 "use",
 281                 format!("{:&>width$}{}", "", receiver_snippet, width = n_refs),
 282                 Applicability::MachineApplicable,
 283             );
 284             return true;
 285         }
 286     }
 287     false
 288 }
 289
 290 /// Walks an expression's ancestors until it finds a non-`AddrOf` expression. Returns the first such
 291 /// expression found (if any) along with the immediately prior expression.
 292 fn skip_addr_of_ancestors<'tcx>(
 293     cx: &LateContext<'tcx>,
 294     mut expr: &'tcx Expr<'tcx>,
 295 ) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 296     while let Some(parent) = get_parent_expr(cx, expr) {
 297         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind {
 298             expr = parent;
 299         } else {
 300             return Some((parent, expr));
 301         }
 302     }
 303     None
 304 }
 305
 306 /// Checks whether an expression is a function or method call and, if so, returns its `DefId`,
 307 /// `Substs`, and arguments.
 308 fn get_callee_substs_and_args<'tcx>(
 309     cx: &LateContext<'tcx>,
 310     expr: &'tcx Expr<'tcx>,
 311 ) -> Option<(DefId, SubstsRef<'tcx>, Option<&'tcx Expr<'tcx>>, &'tcx [Expr<'tcx>])> {
 312     if_chain! {
 313         if let ExprKind::Call(callee, args) = expr.kind;
 314         let callee_ty = cx.typeck_results().expr_ty(callee);
 315         if let ty::FnDef(callee_def_id, _) = callee_ty.kind();
 316         then {
 317             let substs = cx.typeck_results().node_substs(callee.hir_id);
 318             return Some((*callee_def_id, substs, None, args));
 319         }
 320     }
 321     if_chain! {
 322         if let ExprKind::MethodCall(_, recv, args, _) = expr.kind;
 323         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 324         then {
 325             let substs = cx.typeck_results().node_substs(expr.hir_id);
 326             return Some((method_def_id, substs, Some(recv), args));
 327         }
 328     }
 329     None
 330 }
 331
 332 /// Returns the `TraitPredicate`s and `ProjectionPredicate`s for a function's input type.
 333 fn get_input_traits_and_projections<'tcx>(
 334     cx: &LateContext<'tcx>,
 335     callee_def_id: DefId,
 336     input: Ty<'tcx>,
 337 ) -> (Vec<TraitPredicate<'tcx>>, Vec<ProjectionPredicate<'tcx>>) {
 338     let mut trait_predicates = Vec::new();
 339     let mut projection_predicates = Vec::new();
 340     for predicate in cx.tcx.param_env(callee_def_id).caller_bounds() {
 341         match predicate.kind().skip_binder() {
 342             PredicateKind::Trait(trait_predicate) => {
 343                 if trait_predicate.trait_ref.self_ty() == input {
 344                     trait_predicates.push(trait_predicate);
 345                 }
 346             },
 347             PredicateKind::Projection(projection_predicate) => {
 348                 if projection_predicate.projection_ty.self_ty() == input {
 349                     projection_predicates.push(projection_predicate);
 350                 }
 351             },
 352             _ => {},
 353         }
 354     }
 355     (trait_predicates, projection_predicates)
 356 }
 357
 358 fn can_change_type<'a>(cx: &LateContext<'a>, mut expr: &'a Expr<'a>, mut ty: Ty<'a>) -> bool {
 359     for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
 360         match node {
 361             Node::Stmt(_) => return true,
 362             Node::Block(..) => continue,
 363             Node::Item(item) => {
 364                 if let ItemKind::Fn(_, _, body_id) = &item.kind
 365                 && let output_ty = return_ty(cx, item.hir_id())
 366                 && let local_def_id = cx.tcx.hir().local_def_id(item.hir_id())
 367                 && Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 368                     let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, item.hir_id());
 369                     fn_ctxt.can_coerce(ty, output_ty)
 370                 }) {
 371                     if has_lifetime(output_ty) && has_lifetime(ty) {
 372                         return false;
 373                     }
 374                     let body = cx.tcx.hir().body(*body_id);
 375                     let body_expr = &body.value;
 376                     let mut count = 0;
 377                     return find_all_ret_expressions(cx, body_expr, |_| { count += 1; count <= 1 });
 378                 }
 379             }
 380             Node::Expr(parent_expr) => {
 381                 if let Some((callee_def_id, call_substs, recv, call_args)) = get_callee_substs_and_args(cx, parent_expr)
 382                 {
 383                     let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 384                     if let Some(arg_index) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == expr.hir_id)
 385                         && let Some(param_ty) = fn_sig.inputs().get(arg_index)
 386                         && let ty::Param(ParamTy { index: param_index , ..}) = param_ty.kind()
 387                     {
 388                         if fn_sig
 389                             .inputs()
 390                             .iter()
 391                             .enumerate()
 392                             .filter(|(i, _)| *i != arg_index)
 393                             .any(|(_, ty)| ty.contains(*param_ty))
 394                         {
 395                             return false;
 396                         }
 397
 398                         let mut trait_predicates = cx.tcx.param_env(callee_def_id)
 399                             .caller_bounds().iter().filter(|predicate| {
 400                             if let PredicateKind::Trait(trait_predicate) =  predicate.kind().skip_binder()
 401                                 && trait_predicate.trait_ref.self_ty() == *param_ty {
 402                                     true
 403                                 } else {
 404                                 false
 405                             }
 406                         });
 407
 408                         let new_subst = cx.tcx.mk_substs(
 409                             call_substs.iter()
 410                                 .enumerate()
 411                                 .map(|(i, t)|
 412                                      if i == (*param_index as usize) {
 413                                          GenericArg::from(ty)
 414                                      } else {
 415                                          t
 416                                      }));
 417
 418                         if trait_predicates.any(|predicate| {
 419                             let predicate = EarlyBinder(predicate).subst(cx.tcx, new_subst);
 420                             let obligation = Obligation::new(ObligationCause::dummy(), cx.param_env, predicate);
 421                             !cx.tcx
 422                                 .infer_ctxt()
 423                                 .enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation))
 424                         }) {
 425                             return false;
 426                         }
 427
 428                         let output_ty = fn_sig.output();
 429                         if output_ty.contains(*param_ty) {
 430                             if let Ok(new_ty)  = cx.tcx.try_subst_and_normalize_erasing_regions(
 431                                 new_subst, cx.param_env, output_ty) {
 432                                 expr = parent_expr;
 433                                 ty = new_ty;
 434                                 continue;
 435                             }
 436                             return false;
 437                         }
 438
 439                         return true;
 440                     }
 441                 } else if let ExprKind::Block(..) = parent_expr.kind {
 442                     continue;
 443                 }
 444                 return false;
 445             },
 446             _ => return false,
 447         }
 448     }
 449
 450     false
 451 }
 452
 453 fn has_lifetime(ty: Ty<'_>) -> bool {
 454     ty.walk().any(|t| matches!(t.unpack(), GenericArgKind::Lifetime(_)))
 455 }
 456
 457 /// Returns true if the named method is `Iterator::cloned` or `Iterator::copied`.
 458 fn is_cloned_or_copied(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 459     (method_name.as_str() == "cloned" || method_name.as_str() == "copied")
 460         && is_diag_trait_item(cx, method_def_id, sym::Iterator)
 461 }
 462
 463 /// Returns true if the named method can be used to convert the receiver to its "owned"
 464 /// representation.
 465 fn is_to_owned_like<'a>(cx: &LateContext<'a>, call_expr: &Expr<'a>, method_name: Symbol, method_def_id: DefId) -> bool {
 466     is_clone_like(cx, method_name.as_str(), method_def_id)
 467         || is_cow_into_owned(cx, method_name, method_def_id)
 468         || is_to_string_on_string_like(cx, call_expr, method_name, method_def_id)
 469 }
 470
 471 /// Returns true if the named method is `Cow::into_owned`.
 472 fn is_cow_into_owned(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 473     method_name.as_str() == "into_owned" && is_diag_item_method(cx, method_def_id, sym::Cow)
 474 }
 475
 476 /// Returns true if the named method is `ToString::to_string` and it's called on a type that
 477 /// is string-like i.e. implements `AsRef<str>` or `Deref<str>`.
 478 fn is_to_string_on_string_like<'a>(
 479     cx: &LateContext<'_>,
 480     call_expr: &'a Expr<'a>,
 481     method_name: Symbol,
 482     method_def_id: DefId,
 483 ) -> bool {
 484     if method_name != sym::to_string || !is_diag_trait_item(cx, method_def_id, sym::ToString) {
 485         return false;
 486     }
 487
 488     if let Some(substs) = cx.typeck_results().node_substs_opt(call_expr.hir_id)
 489         && let [generic_arg] = substs.as_slice()
 490         && let GenericArgKind::Type(ty) = generic_arg.unpack()
 491         && let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref)
 492         && let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef)
 493         && (implements_trait(cx, ty, deref_trait_id, &[cx.tcx.types.str_.into()]) ||
 494             implements_trait(cx, ty, as_ref_trait_id, &[cx.tcx.types.str_.into()])) {
 495             true
 496         } else {
 497             false
 498         }
 499 }