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 clippy_utils::diagnostics::span_lint_and_sugg;
   4 use clippy_utils::msrvs::{self, Msrv};
   5 use clippy_utils::source::snippet_opt;
   6 use clippy_utils::ty::{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 rustc_errors::Applicability;
  10 use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind, ItemKind, Node};
  11 use rustc_hir_typeck::{FnCtxt, Inherited};
  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::{self, Clause, EarlyBinder, ParamTy, PredicateKind, ProjectionPredicate, TraitPredicate, Ty};
  18 use rustc_span::{sym, Symbol};
  19 use rustc_trait_selection::traits::{query::evaluate_obligation::InferCtxtExt as _, Obligation, ObligationCause};
  20
  21 use super::UNNECESSARY_TO_OWNED;
  22
  23 pub fn check<'tcx>(
  24     cx: &LateContext<'tcx>,
  25     expr: &'tcx Expr<'tcx>,
  26     method_name: Symbol,
  27     receiver: &'tcx Expr<'_>,
  28     args: &'tcx [Expr<'_>],
  29     msrv: &Msrv,
  30 ) {
  31     if_chain! {
  32         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  33         if args.is_empty();
  34         then {
  35             if is_cloned_or_copied(cx, method_name, method_def_id) {
  36                 unnecessary_iter_cloned::check(cx, expr, method_name, receiver);
  37             } else if is_to_owned_like(cx, expr, method_name, method_def_id) {
  38                 // At this point, we know the call is of a `to_owned`-like function. The functions
  39                 // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
  40                 // based on its context, that is, whether it is a referent in an `AddrOf` expression, an
  41                 // argument in a `into_iter` call, or an argument in the call of some other function.
  42                 if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
  43                     return;
  44                 }
  45                 if check_into_iter_call_arg(cx, expr, method_name, receiver, msrv) {
  46                     return;
  47                 }
  48                 check_other_call_arg(cx, expr, method_name, receiver);
  49             }
  50         }
  51     }
  52 }
  53
  54 /// Checks whether `expr` is a referent in an `AddrOf` expression and, if so, determines whether its
  55 /// call of a `to_owned`-like function is unnecessary.
  56 #[allow(clippy::too_many_lines)]
  57 fn check_addr_of_expr(
  58     cx: &LateContext<'_>,
  59     expr: &Expr<'_>,
  60     method_name: Symbol,
  61     method_def_id: DefId,
  62     receiver: &Expr<'_>,
  63 ) -> bool {
  64     if_chain! {
  65         if let Some(parent) = get_parent_expr(cx, expr);
  66         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind;
  67         let adjustments = cx.typeck_results().expr_adjustments(parent).iter().collect::<Vec<_>>();
  68         if let
  69             // For matching uses of `Cow::from`
  70             [
  71                 Adjustment {
  72                     kind: Adjust::Deref(None),
  73                     target: referent_ty,
  74                 },
  75                 Adjustment {
  76                     kind: Adjust::Borrow(_),
  77                     target: target_ty,
  78                 },
  79             ]
  80             // For matching uses of arrays
  81             | [
  82                 Adjustment {
  83                     kind: Adjust::Deref(None),
  84                     target: referent_ty,
  85                 },
  86                 Adjustment {
  87                     kind: Adjust::Borrow(_),
  88                     ..
  89                 },
  90                 Adjustment {
  91                     kind: Adjust::Pointer(_),
  92                     target: target_ty,
  93                 },
  94             ]
  95             // For matching everything else
  96             | [
  97                 Adjustment {
  98                     kind: Adjust::Deref(None),
  99                     target: referent_ty,
 100                 },
 101                 Adjustment {
 102                     kind: Adjust::Deref(Some(OverloadedDeref { .. })),
 103                     ..
 104                 },
 105                 Adjustment {
 106                     kind: Adjust::Borrow(_),
 107                     target: target_ty,
 108                 },
 109             ] = adjustments[..];
 110         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 111         let (target_ty, n_target_refs) = peel_mid_ty_refs(*target_ty);
 112         let (receiver_ty, n_receiver_refs) = peel_mid_ty_refs(receiver_ty);
 113         // Only flag cases satisfying at least one of the following three conditions:
 114         // * the referent and receiver types are distinct
 115         // * the referent/receiver type is a copyable array
 116         // * the method is `Cow::into_owned`
 117         // This restriction is to ensure there is no overlap between `redundant_clone` and this
 118         // lint. It also avoids the following false positive:
 119         //  https://github.com/rust-lang/rust-clippy/issues/8759
 120         //   Arrays are a bit of a corner case. Non-copyable arrays are handled by
 121         // `redundant_clone`, but copyable arrays are not.
 122         if *referent_ty != receiver_ty
 123             || (matches!(referent_ty.kind(), ty::Array(..)) && is_copy(cx, *referent_ty))
 124             || is_cow_into_owned(cx, method_name, method_def_id);
 125         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 126         then {
 127             if receiver_ty == target_ty && n_target_refs >= n_receiver_refs {
 128                 span_lint_and_sugg(
 129                     cx,
 130                     UNNECESSARY_TO_OWNED,
 131                     parent.span,
 132                     &format!("unnecessary use of `{method_name}`"),
 133                     "use",
 134                     format!(
 135                         "{:&>width$}{receiver_snippet}",
 136                         "",
 137                         width = n_target_refs - n_receiver_refs
 138                     ),
 139                     Applicability::MachineApplicable,
 140                 );
 141                 return true;
 142             }
 143             if_chain! {
 144                 if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 145                 if implements_trait(cx, receiver_ty, deref_trait_id, &[]);
 146                 if cx.get_associated_type(receiver_ty, deref_trait_id, "Target") == Some(target_ty);
 147                 then {
 148                     if n_receiver_refs > 0 {
 149                         span_lint_and_sugg(
 150                             cx,
 151                             UNNECESSARY_TO_OWNED,
 152                             parent.span,
 153                             &format!("unnecessary use of `{method_name}`"),
 154                             "use",
 155                             receiver_snippet,
 156                             Applicability::MachineApplicable,
 157                         );
 158                     } else {
 159                         span_lint_and_sugg(
 160                             cx,
 161                             UNNECESSARY_TO_OWNED,
 162                             expr.span.with_lo(receiver.span.hi()),
 163                             &format!("unnecessary use of `{method_name}`"),
 164                             "remove this",
 165                             String::new(),
 166                             Applicability::MachineApplicable,
 167                         );
 168                     }
 169                     return true;
 170                 }
 171             }
 172             if_chain! {
 173                 if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 174                 if implements_trait(cx, receiver_ty, as_ref_trait_id, &[GenericArg::from(target_ty)]);
 175                 then {
 176                     span_lint_and_sugg(
 177                         cx,
 178                         UNNECESSARY_TO_OWNED,
 179                         parent.span,
 180                         &format!("unnecessary use of `{method_name}`"),
 181                         "use",
 182                         format!("{receiver_snippet}.as_ref()"),
 183                         Applicability::MachineApplicable,
 184                     );
 185                     return true;
 186                 }
 187             }
 188         }
 189     }
 190     false
 191 }
 192
 193 /// Checks whether `expr` is an argument in an `into_iter` call and, if so, determines whether its
 194 /// call of a `to_owned`-like function is unnecessary.
 195 fn check_into_iter_call_arg(
 196     cx: &LateContext<'_>,
 197     expr: &Expr<'_>,
 198     method_name: Symbol,
 199     receiver: &Expr<'_>,
 200     msrv: &Msrv,
 201 ) -> bool {
 202     if_chain! {
 203         if let Some(parent) = get_parent_expr(cx, expr);
 204         if let Some(callee_def_id) = fn_def_id(cx, parent);
 205         if is_into_iter(cx, callee_def_id);
 206         if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
 207         let parent_ty = cx.typeck_results().expr_ty(parent);
 208         if implements_trait(cx, parent_ty, iterator_trait_id, &[]);
 209         if let Some(item_ty) = get_iterator_item_ty(cx, parent_ty);
 210         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 211         then {
 212             if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver, true) {
 213                 return true;
 214             }
 215             let cloned_or_copied = if is_copy(cx, item_ty) && msrv.meets(msrvs::ITERATOR_COPIED) {
 216                 "copied"
 217             } else {
 218                 "cloned"
 219             };
 220             // The next suggestion may be incorrect because the removal of the `to_owned`-like
 221             // function could cause the iterator to hold a reference to a resource that is used
 222             // mutably. See https://github.com/rust-lang/rust-clippy/issues/8148.
 223             span_lint_and_sugg(
 224                 cx,
 225                 UNNECESSARY_TO_OWNED,
 226                 parent.span,
 227                 &format!("unnecessary use of `{method_name}`"),
 228                 "use",
 229                 format!("{receiver_snippet}.iter().{cloned_or_copied}()"),
 230                 Applicability::MaybeIncorrect,
 231             );
 232             return true;
 233         }
 234     }
 235     false
 236 }
 237
 238 /// Checks whether `expr` is an argument in a function call and, if so, determines whether its call
 239 /// of a `to_owned`-like function is unnecessary.
 240 fn check_other_call_arg<'tcx>(
 241     cx: &LateContext<'tcx>,
 242     expr: &'tcx Expr<'tcx>,
 243     method_name: Symbol,
 244     receiver: &'tcx Expr<'tcx>,
 245 ) -> bool {
 246     if_chain! {
 247         if let Some((maybe_call, maybe_arg)) = skip_addr_of_ancestors(cx, expr);
 248         if let Some((callee_def_id, _, recv, call_args)) = get_callee_substs_and_args(cx, maybe_call);
 249         let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 250         if let Some(i) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == maybe_arg.hir_id);
 251         if let Some(input) = fn_sig.inputs().get(i);
 252         let (input, n_refs) = peel_mid_ty_refs(*input);
 253         if let (trait_predicates, _) = get_input_traits_and_projections(cx, callee_def_id, input);
 254         if let Some(sized_def_id) = cx.tcx.lang_items().sized_trait();
 255         if let [trait_predicate] = trait_predicates
 256             .iter()
 257             .filter(|trait_predicate| trait_predicate.def_id() != sized_def_id)
 258             .collect::<Vec<_>>()[..];
 259         if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 260         if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 261         if trait_predicate.def_id() == deref_trait_id || trait_predicate.def_id() == as_ref_trait_id;
 262         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 263         // We can't add an `&` when the trait is `Deref` because `Target = &T` won't match
 264         // `Target = T`.
 265         if let Some((n_refs, receiver_ty)) = if n_refs > 0 || is_copy(cx, receiver_ty) {
 266             Some((n_refs, receiver_ty))
 267         } else if trait_predicate.def_id() != deref_trait_id {
 268             Some((1, cx.tcx.mk_ref(
 269                 cx.tcx.lifetimes.re_erased,
 270                 ty::TypeAndMut {
 271                     ty: receiver_ty,
 272                     mutbl: Mutability::Not,
 273                 },
 274             )))
 275         } else {
 276             None
 277         };
 278         if can_change_type(cx, maybe_arg, receiver_ty);
 279         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 280         then {
 281             span_lint_and_sugg(
 282                 cx,
 283                 UNNECESSARY_TO_OWNED,
 284                 maybe_arg.span,
 285                 &format!("unnecessary use of `{method_name}`"),
 286                 "use",
 287                 format!("{:&>n_refs$}{receiver_snippet}", ""),
 288                 Applicability::MachineApplicable,
 289             );
 290             return true;
 291         }
 292     }
 293     false
 294 }
 295
 296 /// Walks an expression's ancestors until it finds a non-`AddrOf` expression. Returns the first such
 297 /// expression found (if any) along with the immediately prior expression.
 298 fn skip_addr_of_ancestors<'tcx>(
 299     cx: &LateContext<'tcx>,
 300     mut expr: &'tcx Expr<'tcx>,
 301 ) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 302     while let Some(parent) = get_parent_expr(cx, expr) {
 303         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind {
 304             expr = parent;
 305         } else {
 306             return Some((parent, expr));
 307         }
 308     }
 309     None
 310 }
 311
 312 /// Checks whether an expression is a function or method call and, if so, returns its `DefId`,
 313 /// `Substs`, and arguments.
 314 fn get_callee_substs_and_args<'tcx>(
 315     cx: &LateContext<'tcx>,
 316     expr: &'tcx Expr<'tcx>,
 317 ) -> Option<(DefId, SubstsRef<'tcx>, Option<&'tcx Expr<'tcx>>, &'tcx [Expr<'tcx>])> {
 318     if_chain! {
 319         if let ExprKind::Call(callee, args) = expr.kind;
 320         let callee_ty = cx.typeck_results().expr_ty(callee);
 321         if let ty::FnDef(callee_def_id, _) = callee_ty.kind();
 322         then {
 323             let substs = cx.typeck_results().node_substs(callee.hir_id);
 324             return Some((*callee_def_id, substs, None, args));
 325         }
 326     }
 327     if_chain! {
 328         if let ExprKind::MethodCall(_, recv, args, _) = expr.kind;
 329         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 330         then {
 331             let substs = cx.typeck_results().node_substs(expr.hir_id);
 332             return Some((method_def_id, substs, Some(recv), args));
 333         }
 334     }
 335     None
 336 }
 337
 338 /// Returns the `TraitPredicate`s and `ProjectionPredicate`s for a function's input type.
 339 fn get_input_traits_and_projections<'tcx>(
 340     cx: &LateContext<'tcx>,
 341     callee_def_id: DefId,
 342     input: Ty<'tcx>,
 343 ) -> (Vec<TraitPredicate<'tcx>>, Vec<ProjectionPredicate<'tcx>>) {
 344     let mut trait_predicates = Vec::new();
 345     let mut projection_predicates = Vec::new();
 346     for predicate in cx.tcx.param_env(callee_def_id).caller_bounds() {
 347         match predicate.kind().skip_binder() {
 348             PredicateKind::Clause(Clause::Trait(trait_predicate)) => {
 349                 if trait_predicate.trait_ref.self_ty() == input {
 350                     trait_predicates.push(trait_predicate);
 351                 }
 352             },
 353             PredicateKind::Clause(Clause::Projection(projection_predicate)) => {
 354                 if projection_predicate.projection_ty.self_ty() == input {
 355                     projection_predicates.push(projection_predicate);
 356                 }
 357             },
 358             _ => {},
 359         }
 360     }
 361     (trait_predicates, projection_predicates)
 362 }
 363
 364 fn can_change_type<'a>(cx: &LateContext<'a>, mut expr: &'a Expr<'a>, mut ty: Ty<'a>) -> bool {
 365     for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
 366         match node {
 367             Node::Stmt(_) => return true,
 368             Node::Block(..) => continue,
 369             Node::Item(item) => {
 370                 if let ItemKind::Fn(_, _, body_id) = &item.kind
 371                 && let output_ty = return_ty(cx, item.hir_id())
 372                 && let local_def_id = cx.tcx.hir().local_def_id(item.hir_id())
 373                 && Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
 374                     let fn_ctxt = FnCtxt::new(inherited, cx.param_env, item.hir_id());
 375                     fn_ctxt.can_coerce(ty, output_ty)
 376                 }) {
 377                     if has_lifetime(output_ty) && has_lifetime(ty) {
 378                         return false;
 379                     }
 380                     let body = cx.tcx.hir().body(*body_id);
 381                     let body_expr = &body.value;
 382                     let mut count = 0;
 383                     return find_all_ret_expressions(cx, body_expr, |_| { count += 1; count <= 1 });
 384                 }
 385             }
 386             Node::Expr(parent_expr) => {
 387                 if let Some((callee_def_id, call_substs, recv, call_args)) = get_callee_substs_and_args(cx, parent_expr)
 388                 {
 389                     let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 390                     if let Some(arg_index) = recv.into_iter().chain(call_args).position(|arg| arg.hir_id == expr.hir_id)
 391                         && let Some(param_ty) = fn_sig.inputs().get(arg_index)
 392                         && let ty::Param(ParamTy { index: param_index , ..}) = param_ty.kind()
 393                         // https://github.com/rust-lang/rust-clippy/issues/9504 and https://github.com/rust-lang/rust-clippy/issues/10021
 394                         && (*param_index as usize) < call_substs.len()
 395                     {
 396                         if fn_sig
 397                             .inputs()
 398                             .iter()
 399                             .enumerate()
 400                             .filter(|(i, _)| *i != arg_index)
 401                             .any(|(_, ty)| ty.contains(*param_ty))
 402                         {
 403                             return false;
 404                         }
 405
 406                         let mut trait_predicates = cx.tcx.param_env(callee_def_id)
 407                             .caller_bounds().iter().filter(|predicate| {
 408                             if let PredicateKind::Clause(Clause::Trait(trait_predicate))
 409                                     = predicate.kind().skip_binder()
 410                                 && trait_predicate.trait_ref.self_ty() == *param_ty
 411                             {
 412                                 true
 413                             } else {
 414                                 false
 415                             }
 416                         });
 417
 418                         let new_subst = cx.tcx.mk_substs(
 419                             call_substs.iter()
 420                                 .enumerate()
 421                                 .map(|(i, t)|
 422                                      if i == (*param_index as usize) {
 423                                          GenericArg::from(ty)
 424                                      } else {
 425                                          t
 426                                      }));
 427
 428                         if trait_predicates.any(|predicate| {
 429                             let predicate = EarlyBinder(predicate).subst(cx.tcx, new_subst);
 430                             let obligation = Obligation::new(cx.tcx, ObligationCause::dummy(), cx.param_env, predicate);
 431                             !cx.tcx.infer_ctxt().build().predicate_must_hold_modulo_regions(&obligation)
 432                         }) {
 433                             return false;
 434                         }
 435
 436                         let output_ty = fn_sig.output();
 437                         if output_ty.contains(*param_ty) {
 438                             if let Ok(new_ty)  = cx.tcx.try_subst_and_normalize_erasing_regions(
 439                                 new_subst, cx.param_env, output_ty) {
 440                                 expr = parent_expr;
 441                                 ty = new_ty;
 442                                 continue;
 443                             }
 444                             return false;
 445                         }
 446
 447                         return true;
 448                     }
 449                 } else if let ExprKind::Block(..) = parent_expr.kind {
 450                     continue;
 451                 }
 452                 return false;
 453             },
 454             _ => return false,
 455         }
 456     }
 457
 458     false
 459 }
 460
 461 fn has_lifetime(ty: Ty<'_>) -> bool {
 462     ty.walk().any(|t| matches!(t.unpack(), GenericArgKind::Lifetime(_)))
 463 }
 464
 465 /// Returns true if the named method is `Iterator::cloned` or `Iterator::copied`.
 466 fn is_cloned_or_copied(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 467     (method_name.as_str() == "cloned" || method_name.as_str() == "copied")
 468         && is_diag_trait_item(cx, method_def_id, sym::Iterator)
 469 }
 470
 471 /// Returns true if the named method can be used to convert the receiver to its "owned"
 472 /// representation.
 473 fn is_to_owned_like<'a>(cx: &LateContext<'a>, call_expr: &Expr<'a>, method_name: Symbol, method_def_id: DefId) -> bool {
 474     is_clone_like(cx, method_name.as_str(), method_def_id)
 475         || is_cow_into_owned(cx, method_name, method_def_id)
 476         || is_to_string_on_string_like(cx, call_expr, method_name, method_def_id)
 477 }
 478
 479 /// Returns true if the named method is `Cow::into_owned`.
 480 fn is_cow_into_owned(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 481     method_name.as_str() == "into_owned" && is_diag_item_method(cx, method_def_id, sym::Cow)
 482 }
 483
 484 /// Returns true if the named method is `ToString::to_string` and it's called on a type that
 485 /// is string-like i.e. implements `AsRef<str>` or `Deref<Target = str>`.
 486 fn is_to_string_on_string_like<'a>(
 487     cx: &LateContext<'_>,
 488     call_expr: &'a Expr<'a>,
 489     method_name: Symbol,
 490     method_def_id: DefId,
 491 ) -> bool {
 492     if method_name != sym::to_string || !is_diag_trait_item(cx, method_def_id, sym::ToString) {
 493         return false;
 494     }
 495
 496     if let Some(substs) = cx.typeck_results().node_substs_opt(call_expr.hir_id)
 497         && let [generic_arg] = substs.as_slice()
 498         && let GenericArgKind::Type(ty) = generic_arg.unpack()
 499         && let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref)
 500         && let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef)
 501         && (cx.get_associated_type(ty, deref_trait_id, "Target") == Some(cx.tcx.types.str_) ||
 502             implements_trait(cx, ty, as_ref_trait_id, &[cx.tcx.types.str_.into()])) {
 503             true
 504         } else {
 505             false
 506         }
 507 }