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::source::snippet_opt;
   5 use clippy_utils::ty::{get_associated_type, get_iterator_item_ty, implements_trait, is_copy, peel_mid_ty_refs};
   6 use clippy_utils::{fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item};
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind};
   9 use rustc_lint::LateContext;
  10 use rustc_middle::mir::Mutability;
  11 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref};
  12 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  13 use rustc_middle::ty::{self, PredicateKind, ProjectionPredicate, TraitPredicate, Ty};
  14 use rustc_span::{sym, Symbol};
  15 use std::cmp::max;
  16
  17 use super::UNNECESSARY_TO_OWNED;
  18
  19 pub fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: Symbol, args: &'tcx [Expr<'tcx>]) {
  20     if_chain! {
  21         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  22         if let [receiver] = args;
  23         then {
  24             if is_cloned_or_copied(cx, method_name, method_def_id) {
  25                 unnecessary_iter_cloned::check(cx, expr, method_name, receiver);
  26             } else if is_to_owned_like(cx, method_name, method_def_id) {
  27                 // At this point, we know the call is of a `to_owned`-like function. The functions
  28                 // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
  29                 // based on its context, that is, whether it is a referent in an `AddrOf` expression, an
  30                 // argument in a `into_iter` call, or an argument in the call of some other function.
  31                 if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
  32                     return;
  33                 }
  34                 if check_into_iter_call_arg(cx, expr, method_name, receiver) {
  35                     return;
  36                 }
  37                 check_other_call_arg(cx, expr, method_name, receiver);
  38             }
  39         }
  40     }
  41 }
  42
  43 /// Checks whether `expr` is a referent in an `AddrOf` expression and, if so, determines whether its
  44 /// call of a `to_owned`-like function is unnecessary.
  45 #[allow(clippy::too_many_lines)]
  46 fn check_addr_of_expr(
  47     cx: &LateContext<'_>,
  48     expr: &Expr<'_>,
  49     method_name: Symbol,
  50     method_def_id: DefId,
  51     receiver: &Expr<'_>,
  52 ) -> bool {
  53     if_chain! {
  54         if let Some(parent) = get_parent_expr(cx, expr);
  55         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind;
  56         let adjustments = cx.typeck_results().expr_adjustments(parent).iter().collect::<Vec<_>>();
  57         if let Some(target_ty) = match adjustments[..]
  58         {
  59             // For matching uses of `Cow::from`
  60             [
  61                 Adjustment {
  62                     kind: Adjust::Deref(None),
  63                     ..
  64                 },
  65                 Adjustment {
  66                     kind: Adjust::Borrow(_),
  67                     target: target_ty,
  68                 },
  69             ]
  70             // For matching uses of arrays
  71             | [
  72                 Adjustment {
  73                     kind: Adjust::Deref(None),
  74                     ..
  75                 },
  76                 Adjustment {
  77                     kind: Adjust::Borrow(_),
  78                     ..
  79                 },
  80                 Adjustment {
  81                     kind: Adjust::Pointer(_),
  82                     target: target_ty,
  83                 },
  84             ]
  85             // For matching everything else
  86             | [
  87                 Adjustment {
  88                     kind: Adjust::Deref(None),
  89                     ..
  90                 },
  91                 Adjustment {
  92                     kind: Adjust::Deref(Some(OverloadedDeref { .. })),
  93                     ..
  94                 },
  95                 Adjustment {
  96                     kind: Adjust::Borrow(_),
  97                     target: target_ty,
  98                 },
  99             ] => Some(target_ty),
 100             _ => None,
 101         };
 102         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 103         // Only flag cases where the receiver is copyable or the method is `Cow::into_owned`. This
 104         // restriction is to ensure there is not overlap between `redundant_clone` and this lint.
 105         if is_copy(cx, receiver_ty) || is_cow_into_owned(cx, method_name, method_def_id);
 106         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 107         then {
 108             let (target_ty, n_target_refs) = peel_mid_ty_refs(target_ty);
 109             let (receiver_ty, n_receiver_refs) = peel_mid_ty_refs(receiver_ty);
 110             if receiver_ty == target_ty && n_target_refs >= n_receiver_refs {
 111                 span_lint_and_sugg(
 112                     cx,
 113                     UNNECESSARY_TO_OWNED,
 114                     parent.span,
 115                     &format!("unnecessary use of `{}`", method_name),
 116                     "use",
 117                     format!("{:&>width$}{}", "", receiver_snippet, width = n_target_refs - n_receiver_refs),
 118                     Applicability::MachineApplicable,
 119                 );
 120                 return true;
 121             }
 122             if_chain! {
 123                 if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 124                 if implements_trait(cx, receiver_ty, deref_trait_id, &[]);
 125                 if get_associated_type(cx, receiver_ty, deref_trait_id, "Target") == Some(target_ty);
 126                 then {
 127                     if n_receiver_refs > 0 {
 128                         span_lint_and_sugg(
 129                             cx,
 130                             UNNECESSARY_TO_OWNED,
 131                             parent.span,
 132                             &format!("unnecessary use of `{}`", method_name),
 133                             "use",
 134                             receiver_snippet,
 135                             Applicability::MachineApplicable,
 136                         );
 137                     } else {
 138                         span_lint_and_sugg(
 139                             cx,
 140                             UNNECESSARY_TO_OWNED,
 141                             expr.span.with_lo(receiver.span.hi()),
 142                             &format!("unnecessary use of `{}`", method_name),
 143                             "remove this",
 144                             String::new(),
 145                             Applicability::MachineApplicable,
 146                         );
 147                     }
 148                     return true;
 149                 }
 150             }
 151             if_chain! {
 152                 if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 153                 if implements_trait(cx, receiver_ty, as_ref_trait_id, &[GenericArg::from(target_ty)]);
 154                 then {
 155                     span_lint_and_sugg(
 156                         cx,
 157                         UNNECESSARY_TO_OWNED,
 158                         parent.span,
 159                         &format!("unnecessary use of `{}`", method_name),
 160                         "use",
 161                         format!("{}.as_ref()", receiver_snippet),
 162                         Applicability::MachineApplicable,
 163                     );
 164                     return true;
 165                 }
 166             }
 167         }
 168     }
 169     false
 170 }
 171
 172 /// Checks whether `expr` is an argument in an `into_iter` call and, if so, determines whether its
 173 /// call of a `to_owned`-like function is unnecessary.
 174 fn check_into_iter_call_arg(cx: &LateContext<'_>, expr: &Expr<'_>, method_name: Symbol, receiver: &Expr<'_>) -> bool {
 175     if_chain! {
 176         if let Some(parent) = get_parent_expr(cx, expr);
 177         if let Some(callee_def_id) = fn_def_id(cx, parent);
 178         if is_into_iter(cx, callee_def_id);
 179         if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
 180         let parent_ty = cx.typeck_results().expr_ty(parent);
 181         if implements_trait(cx, parent_ty, iterator_trait_id, &[]);
 182         if let Some(item_ty) = get_iterator_item_ty(cx, parent_ty);
 183         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 184         then {
 185             if unnecessary_iter_cloned::check_for_loop_iter(
 186                 cx,
 187                 parent,
 188                 method_name,
 189                 receiver,
 190                 true,
 191             ) {
 192                 return true;
 193             }
 194             let cloned_or_copied = if is_copy(cx, item_ty) {
 195                 "copied"
 196             } else {
 197                 "cloned"
 198             };
 199             // The next suggestion may be incorrect because the removal of the `to_owned`-like
 200             // function could cause the iterator to hold a reference to a resource that is used
 201             // mutably. See https://github.com/rust-lang/rust-clippy/issues/8148.
 202             span_lint_and_sugg(
 203                 cx,
 204                 UNNECESSARY_TO_OWNED,
 205                 parent.span,
 206                 &format!("unnecessary use of `{}`", method_name),
 207                 "use",
 208                 format!("{}.iter().{}()", receiver_snippet, cloned_or_copied),
 209                 Applicability::MaybeIncorrect,
 210             );
 211             return true;
 212         }
 213     }
 214     false
 215 }
 216
 217 /// Checks whether `expr` is an argument in a function call and, if so, determines whether its call
 218 /// of a `to_owned`-like function is unnecessary.
 219 fn check_other_call_arg<'tcx>(
 220     cx: &LateContext<'tcx>,
 221     expr: &'tcx Expr<'tcx>,
 222     method_name: Symbol,
 223     receiver: &'tcx Expr<'tcx>,
 224 ) -> bool {
 225     if_chain! {
 226         if let Some((maybe_call, maybe_arg)) = skip_addr_of_ancestors(cx, expr);
 227         if let Some((callee_def_id, call_substs, call_args)) = get_callee_substs_and_args(cx, maybe_call);
 228         let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
 229         if let Some(i) = call_args.iter().position(|arg| arg.hir_id == maybe_arg.hir_id);
 230         if let Some(input) = fn_sig.inputs().get(i);
 231         let (input, n_refs) = peel_mid_ty_refs(input);
 232         if let (trait_predicates, projection_predicates) = get_input_traits_and_projections(cx, callee_def_id, input);
 233         if let Some(sized_def_id) = cx.tcx.lang_items().sized_trait();
 234         if let [trait_predicate] = trait_predicates
 235             .iter()
 236             .filter(|trait_predicate| trait_predicate.def_id() != sized_def_id)
 237             .collect::<Vec<_>>()[..];
 238         if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
 239         if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
 240         let receiver_ty = cx.typeck_results().expr_ty(receiver);
 241         // If the callee has type parameters, they could appear in `projection_predicate.ty` or the
 242         // types of `trait_predicate.trait_ref.substs`.
 243         if if trait_predicate.def_id() == deref_trait_id {
 244             if let [projection_predicate] = projection_predicates[..] {
 245                 let normalized_ty =
 246                     cx.tcx.subst_and_normalize_erasing_regions(call_substs, cx.param_env, projection_predicate.term);
 247                 implements_trait(cx, receiver_ty, deref_trait_id, &[])
 248                     && get_associated_type(cx, receiver_ty, deref_trait_id,
 249                     "Target").map_or(false, |ty| ty::Term::Ty(ty) == normalized_ty)
 250             } else {
 251                 false
 252             }
 253         } else if trait_predicate.def_id() == as_ref_trait_id {
 254             let composed_substs = compose_substs(
 255                 cx,
 256                 &trait_predicate.trait_ref.substs.iter().skip(1).collect::<Vec<_>>()[..],
 257                 call_substs
 258             );
 259             implements_trait(cx, receiver_ty, as_ref_trait_id, &composed_substs)
 260         } else {
 261             false
 262         };
 263         // We can't add an `&` when the trait is `Deref` because `Target = &T` won't match
 264         // `Target = T`.
 265         if n_refs > 0 || is_copy(cx, receiver_ty) || trait_predicate.def_id() != deref_trait_id;
 266         let n_refs = max(n_refs, if is_copy(cx, receiver_ty) { 0 } else { 1 });
 267         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
 268         then {
 269             span_lint_and_sugg(
 270                 cx,
 271                 UNNECESSARY_TO_OWNED,
 272                 maybe_arg.span,
 273                 &format!("unnecessary use of `{}`", method_name),
 274                 "use",
 275                 format!("{:&>width$}{}", "", receiver_snippet, width = n_refs),
 276                 Applicability::MachineApplicable,
 277             );
 278             return true;
 279         }
 280     }
 281     false
 282 }
 283
 284 /// Walks an expression's ancestors until it finds a non-`AddrOf` expression. Returns the first such
 285 /// expression found (if any) along with the immediately prior expression.
 286 fn skip_addr_of_ancestors<'tcx>(
 287     cx: &LateContext<'tcx>,
 288     mut expr: &'tcx Expr<'tcx>,
 289 ) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 290     while let Some(parent) = get_parent_expr(cx, expr) {
 291         if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind {
 292             expr = parent;
 293         } else {
 294             return Some((parent, expr));
 295         }
 296     }
 297     None
 298 }
 299
 300 /// Checks whether an expression is a function or method call and, if so, returns its `DefId`,
 301 /// `Substs`, and arguments.
 302 fn get_callee_substs_and_args<'tcx>(
 303     cx: &LateContext<'tcx>,
 304     expr: &'tcx Expr<'tcx>,
 305 ) -> Option<(DefId, SubstsRef<'tcx>, &'tcx [Expr<'tcx>])> {
 306     if_chain! {
 307         if let ExprKind::Call(callee, args) = expr.kind;
 308         let callee_ty = cx.typeck_results().expr_ty(callee);
 309         if let ty::FnDef(callee_def_id, _) = callee_ty.kind();
 310         then {
 311             let substs = cx.typeck_results().node_substs(callee.hir_id);
 312             return Some((*callee_def_id, substs, args));
 313         }
 314     }
 315     if_chain! {
 316         if let ExprKind::MethodCall(_, _, args, _) = expr.kind;
 317         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 318         then {
 319             let substs = cx.typeck_results().node_substs(expr.hir_id);
 320             return Some((method_def_id, substs, args));
 321         }
 322     }
 323     None
 324 }
 325
 326 /// Returns the `TraitPredicate`s and `ProjectionPredicate`s for a function's input type.
 327 fn get_input_traits_and_projections<'tcx>(
 328     cx: &LateContext<'tcx>,
 329     callee_def_id: DefId,
 330     input: Ty<'tcx>,
 331 ) -> (Vec<TraitPredicate<'tcx>>, Vec<ProjectionPredicate<'tcx>>) {
 332     let mut trait_predicates = Vec::new();
 333     let mut projection_predicates = Vec::new();
 334     for (predicate, _) in cx.tcx.predicates_of(callee_def_id).predicates.iter() {
 335         // `substs` should have 1 + n elements. The first is the type on the left hand side of an
 336         // `as`. The remaining n are trait parameters.
 337         let is_input_substs = |substs: SubstsRef<'tcx>| {
 338             if_chain! {
 339                 if let Some(arg) = substs.iter().next();
 340                 if let GenericArgKind::Type(arg_ty) = arg.unpack();
 341                 if arg_ty == input;
 342                 then {
 343                     true
 344                 } else {
 345                     false
 346                 }
 347             }
 348         };
 349         match predicate.kind().skip_binder() {
 350             PredicateKind::Trait(trait_predicate) => {
 351                 if is_input_substs(trait_predicate.trait_ref.substs) {
 352                     trait_predicates.push(trait_predicate);
 353                 }
 354             },
 355             PredicateKind::Projection(projection_predicate) => {
 356                 if is_input_substs(projection_predicate.projection_ty.substs) {
 357                     projection_predicates.push(projection_predicate);
 358                 }
 359             },
 360             _ => {},
 361         }
 362     }
 363     (trait_predicates, projection_predicates)
 364 }
 365
 366 /// Composes two substitutions by applying the latter to the types of the former.
 367 fn compose_substs<'tcx>(
 368     cx: &LateContext<'tcx>,
 369     left: &[GenericArg<'tcx>],
 370     right: SubstsRef<'tcx>,
 371 ) -> Vec<GenericArg<'tcx>> {
 372     left.iter()
 373         .map(|arg| {
 374             if let GenericArgKind::Type(arg_ty) = arg.unpack() {
 375                 let normalized_ty = cx.tcx.subst_and_normalize_erasing_regions(right, cx.param_env, arg_ty);
 376                 GenericArg::from(normalized_ty)
 377             } else {
 378                 *arg
 379             }
 380         })
 381         .collect()
 382 }
 383
 384 /// Returns true if the named method is `Iterator::cloned` or `Iterator::copied`.
 385 fn is_cloned_or_copied(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 386     (method_name.as_str() == "cloned" || method_name.as_str() == "copied")
 387         && is_diag_trait_item(cx, method_def_id, sym::Iterator)
 388 }
 389
 390 /// Returns true if the named method can be used to convert the receiver to its "owned"
 391 /// representation.
 392 fn is_to_owned_like(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 393     is_clone_like(cx, &*method_name.as_str(), method_def_id)
 394         || is_cow_into_owned(cx, method_name, method_def_id)
 395         || is_to_string(cx, method_name, method_def_id)
 396 }
 397
 398 /// Returns true if the named method is `Cow::into_owned`.
 399 fn is_cow_into_owned(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 400     method_name.as_str() == "into_owned" && is_diag_item_method(cx, method_def_id, sym::Cow)
 401 }
 402
 403 /// Returns true if the named method is `ToString::to_string`.
 404 fn is_to_string(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
 405     method_name.as_str() == "to_string" && is_diag_trait_item(cx, method_def_id, sym::ToString)
 406 }