src/tools/clippy/clippy_lints/src/ptr.rs

   1 //! Checks for usage of  `&Vec[_]` and `&String`.
   2
   3 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
   4 use clippy_utils::source::snippet_opt;
   5 use clippy_utils::ty::expr_sig;
   6 use clippy_utils::visitors::contains_unsafe_block;
   7 use clippy_utils::{get_expr_use_or_unification_node, is_lint_allowed, path_def_id, path_to_local, paths};
   8 use if_chain::if_chain;
   9 use rustc_errors::{Applicability, MultiSpan};
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::hir_id::HirIdMap;
  12 use rustc_hir::intravisit::{walk_expr, Visitor};
  13 use rustc_hir::{
  14     self as hir, AnonConst, BinOpKind, BindingAnnotation, Body, Expr, ExprKind, FnRetTy, FnSig, GenericArg,
  15     ImplItemKind, ItemKind, Lifetime, LifetimeName, Mutability, Node, Param, ParamName, PatKind, QPath, TraitFn,
  16     TraitItem, TraitItemKind, TyKind, Unsafety,
  17 };
  18 use rustc_lint::{LateContext, LateLintPass};
  19 use rustc_middle::hir::nested_filter;
  20 use rustc_middle::ty::{self, Ty};
  21 use rustc_session::{declare_lint_pass, declare_tool_lint};
  22 use rustc_span::source_map::Span;
  23 use rustc_span::sym;
  24 use rustc_span::symbol::Symbol;
  25 use std::fmt;
  26 use std::iter;
  27
  28 declare_clippy_lint! {
  29     /// ### What it does
  30     /// This lint checks for function arguments of type `&String`, `&Vec`,
  31     /// `&PathBuf`, and `Cow<_>`. It will also suggest you replace `.clone()` calls
  32     /// with the appropriate `.to_owned()`/`to_string()` calls.
  33     ///
  34     /// ### Why is this bad?
  35     /// Requiring the argument to be of the specific size
  36     /// makes the function less useful for no benefit; slices in the form of `&[T]`
  37     /// or `&str` usually suffice and can be obtained from other types, too.
  38     ///
  39     /// ### Known problems
  40     /// There may be `fn(&Vec)`-typed references pointing to your function.
  41     /// If you have them, you will get a compiler error after applying this lint's
  42     /// suggestions. You then have the choice to undo your changes or change the
  43     /// type of the reference.
  44     ///
  45     /// Note that if the function is part of your public interface, there may be
  46     /// other crates referencing it, of which you may not be aware. Carefully
  47     /// deprecate the function before applying the lint suggestions in this case.
  48     ///
  49     /// ### Example
  50     /// ```ignore
  51     /// fn foo(&Vec<u32>) { .. }
  52     /// ```
  53     ///
  54     /// Use instead:
  55     /// ```ignore
  56     /// fn foo(&[u32]) { .. }
  57     /// ```
  58     #[clippy::version = "pre 1.29.0"]
  59     pub PTR_ARG,
  60     style,
  61     "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
  62 }
  63
  64 declare_clippy_lint! {
  65     /// ### What it does
  66     /// This lint checks for equality comparisons with `ptr::null`
  67     ///
  68     /// ### Why is this bad?
  69     /// It's easier and more readable to use the inherent
  70     /// `.is_null()`
  71     /// method instead
  72     ///
  73     /// ### Example
  74     /// ```rust,ignore
  75     /// use std::ptr;
  76     ///
  77     /// if x == ptr::null {
  78     ///     // ..
  79     /// }
  80     /// ```
  81     ///
  82     /// Use instead:
  83     /// ```rust,ignore
  84     /// if x.is_null() {
  85     ///     // ..
  86     /// }
  87     /// ```
  88     #[clippy::version = "pre 1.29.0"]
  89     pub CMP_NULL,
  90     style,
  91     "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead"
  92 }
  93
  94 declare_clippy_lint! {
  95     /// ### What it does
  96     /// This lint checks for functions that take immutable references and return
  97     /// mutable ones. This will not trigger if no unsafe code exists as there
  98     /// are multiple safe functions which will do this transformation
  99     ///
 100     /// To be on the conservative side, if there's at least one mutable
 101     /// reference with the output lifetime, this lint will not trigger.
 102     ///
 103     /// ### Why is this bad?
 104     /// Creating a mutable reference which can be repeatably derived from an
 105     /// immutable reference is unsound as it allows creating multiple live
 106     /// mutable references to the same object.
 107     ///
 108     /// This [error](https://github.com/rust-lang/rust/issues/39465) actually
 109     /// lead to an interim Rust release 1.15.1.
 110     ///
 111     /// ### Known problems
 112     /// This pattern is used by memory allocators to allow allocating multiple
 113     /// objects while returning mutable references to each one. So long as
 114     /// different mutable references are returned each time such a function may
 115     /// be safe.
 116     ///
 117     /// ### Example
 118     /// ```ignore
 119     /// fn foo(&Foo) -> &mut Bar { .. }
 120     /// ```
 121     #[clippy::version = "pre 1.29.0"]
 122     pub MUT_FROM_REF,
 123     correctness,
 124     "fns that create mutable refs from immutable ref args"
 125 }
 126
 127 declare_clippy_lint! {
 128     /// ### What it does
 129     /// This lint checks for invalid usages of `ptr::null`.
 130     ///
 131     /// ### Why is this bad?
 132     /// This causes undefined behavior.
 133     ///
 134     /// ### Example
 135     /// ```ignore
 136     /// // Undefined behavior
 137     /// unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
 138     /// ```
 139     ///
 140     /// Use instead:
 141     /// ```ignore
 142     /// unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
 143     /// ```
 144     #[clippy::version = "1.53.0"]
 145     pub INVALID_NULL_PTR_USAGE,
 146     correctness,
 147     "invalid usage of a null pointer, suggesting `NonNull::dangling()` instead"
 148 }
 149
 150 declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF, INVALID_NULL_PTR_USAGE]);
 151
 152 impl<'tcx> LateLintPass<'tcx> for Ptr {
 153     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 154         if let TraitItemKind::Fn(sig, trait_method) = &item.kind {
 155             if matches!(trait_method, TraitFn::Provided(_)) {
 156                 // Handled by check body.
 157                 return;
 158             }
 159
 160             check_mut_from_ref(cx, sig, None);
 161             for arg in check_fn_args(
 162                 cx,
 163                 cx.tcx.fn_sig(item.def_id).skip_binder().inputs(),
 164                 sig.decl.inputs,
 165                 &[],
 166             )
 167             .filter(|arg| arg.mutability() == Mutability::Not)
 168             {
 169                 span_lint_and_sugg(
 170                     cx,
 171                     PTR_ARG,
 172                     arg.span,
 173                     &arg.build_msg(),
 174                     "change this to",
 175                     format!("{}{}", arg.ref_prefix, arg.deref_ty.display(cx)),
 176                     Applicability::Unspecified,
 177                 );
 178             }
 179         }
 180     }
 181
 182     fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
 183         let hir = cx.tcx.hir();
 184         let mut parents = hir.parent_iter(body.value.hir_id);
 185         let (item_id, sig, is_trait_item) = match parents.next() {
 186             Some((_, Node::Item(i))) => {
 187                 if let ItemKind::Fn(sig, ..) = &i.kind {
 188                     (i.def_id, sig, false)
 189                 } else {
 190                     return;
 191                 }
 192             },
 193             Some((_, Node::ImplItem(i))) => {
 194                 if !matches!(parents.next(),
 195                     Some((_, Node::Item(i))) if matches!(&i.kind, ItemKind::Impl(i) if i.of_trait.is_none())
 196                 ) {
 197                     return;
 198                 }
 199                 if let ImplItemKind::Fn(sig, _) = &i.kind {
 200                     (i.def_id, sig, false)
 201                 } else {
 202                     return;
 203                 }
 204             },
 205             Some((_, Node::TraitItem(i))) => {
 206                 if let TraitItemKind::Fn(sig, _) = &i.kind {
 207                     (i.def_id, sig, true)
 208                 } else {
 209                     return;
 210                 }
 211             },
 212             _ => return,
 213         };
 214
 215         check_mut_from_ref(cx, sig, Some(body));
 216         let decl = sig.decl;
 217         let sig = cx.tcx.fn_sig(item_id).skip_binder();
 218         let lint_args: Vec<_> = check_fn_args(cx, sig.inputs(), decl.inputs, body.params)
 219             .filter(|arg| !is_trait_item || arg.mutability() == Mutability::Not)
 220             .collect();
 221         let results = check_ptr_arg_usage(cx, body, &lint_args);
 222
 223         for (result, args) in results.iter().zip(lint_args.iter()).filter(|(r, _)| !r.skip) {
 224             span_lint_and_then(cx, PTR_ARG, args.span, &args.build_msg(), |diag| {
 225                 diag.multipart_suggestion(
 226                     "change this to",
 227                     iter::once((args.span, format!("{}{}", args.ref_prefix, args.deref_ty.display(cx))))
 228                         .chain(result.replacements.iter().map(|r| {
 229                             (
 230                                 r.expr_span,
 231                                 format!("{}{}", snippet_opt(cx, r.self_span).unwrap(), r.replacement),
 232                             )
 233                         }))
 234                         .collect(),
 235                     Applicability::Unspecified,
 236                 );
 237             });
 238         }
 239     }
 240
 241     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 242         if let ExprKind::Binary(ref op, l, r) = expr.kind {
 243             if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(cx, l) || is_null_path(cx, r)) {
 244                 span_lint(
 245                     cx,
 246                     CMP_NULL,
 247                     expr.span,
 248                     "comparing with null is better expressed by the `.is_null()` method",
 249                 );
 250             }
 251         } else {
 252             check_invalid_ptr_usage(cx, expr);
 253         }
 254     }
 255 }
 256
 257 fn check_invalid_ptr_usage<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 258     // (fn_path, arg_indices) - `arg_indices` are the `arg` positions where null would cause U.B.
 259     const INVALID_NULL_PTR_USAGE_TABLE: [(&[&str], &[usize]); 16] = [
 260         (&paths::SLICE_FROM_RAW_PARTS, &[0]),
 261         (&paths::SLICE_FROM_RAW_PARTS_MUT, &[0]),
 262         (&paths::PTR_COPY, &[0, 1]),
 263         (&paths::PTR_COPY_NONOVERLAPPING, &[0, 1]),
 264         (&paths::PTR_READ, &[0]),
 265         (&paths::PTR_READ_UNALIGNED, &[0]),
 266         (&paths::PTR_READ_VOLATILE, &[0]),
 267         (&paths::PTR_REPLACE, &[0]),
 268         (&paths::PTR_SLICE_FROM_RAW_PARTS, &[0]),
 269         (&paths::PTR_SLICE_FROM_RAW_PARTS_MUT, &[0]),
 270         (&paths::PTR_SWAP, &[0, 1]),
 271         (&paths::PTR_SWAP_NONOVERLAPPING, &[0, 1]),
 272         (&paths::PTR_WRITE, &[0]),
 273         (&paths::PTR_WRITE_UNALIGNED, &[0]),
 274         (&paths::PTR_WRITE_VOLATILE, &[0]),
 275         (&paths::PTR_WRITE_BYTES, &[0]),
 276     ];
 277
 278     if_chain! {
 279         if let ExprKind::Call(fun, args) = expr.kind;
 280         if let ExprKind::Path(ref qpath) = fun.kind;
 281         if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
 282         let fun_def_path = cx.get_def_path(fun_def_id).into_iter().map(Symbol::to_ident_string).collect::<Vec<_>>();
 283         if let Some(&(_, arg_indices)) = INVALID_NULL_PTR_USAGE_TABLE
 284             .iter()
 285             .find(|&&(fn_path, _)| fn_path == fun_def_path);
 286         then {
 287             for &arg_idx in arg_indices {
 288                 if let Some(arg) = args.get(arg_idx).filter(|arg| is_null_path(cx, arg)) {
 289                     span_lint_and_sugg(
 290                         cx,
 291                         INVALID_NULL_PTR_USAGE,
 292                         arg.span,
 293                         "pointer must be non-null",
 294                         "change this to",
 295                         "core::ptr::NonNull::dangling().as_ptr()".to_string(),
 296                         Applicability::MachineApplicable,
 297                     );
 298                 }
 299             }
 300         }
 301     }
 302 }
 303
 304 #[derive(Default)]
 305 struct PtrArgResult {
 306     skip: bool,
 307     replacements: Vec<PtrArgReplacement>,
 308 }
 309
 310 struct PtrArgReplacement {
 311     expr_span: Span,
 312     self_span: Span,
 313     replacement: &'static str,
 314 }
 315
 316 struct PtrArg<'tcx> {
 317     idx: usize,
 318     span: Span,
 319     ty_did: DefId,
 320     ty_name: Symbol,
 321     method_renames: &'static [(&'static str, &'static str)],
 322     ref_prefix: RefPrefix,
 323     deref_ty: DerefTy<'tcx>,
 324 }
 325 impl PtrArg<'_> {
 326     fn build_msg(&self) -> String {
 327         format!(
 328             "writing `&{}{}` instead of `&{}{}` involves a new object where a slice will do",
 329             self.ref_prefix.mutability.prefix_str(),
 330             self.ty_name,
 331             self.ref_prefix.mutability.prefix_str(),
 332             self.deref_ty.argless_str(),
 333         )
 334     }
 335
 336     fn mutability(&self) -> Mutability {
 337         self.ref_prefix.mutability
 338     }
 339 }
 340
 341 struct RefPrefix {
 342     lt: LifetimeName,
 343     mutability: Mutability,
 344 }
 345 impl fmt::Display for RefPrefix {
 346     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 347         use fmt::Write;
 348         f.write_char('&')?;
 349         match self.lt {
 350             LifetimeName::Param(_, ParamName::Plain(name)) => {
 351                 name.fmt(f)?;
 352                 f.write_char(' ')?;
 353             },
 354             LifetimeName::Underscore => f.write_str("'_ ")?,
 355             LifetimeName::Static => f.write_str("'static ")?,
 356             _ => (),
 357         }
 358         f.write_str(self.mutability.prefix_str())
 359     }
 360 }
 361
 362 struct DerefTyDisplay<'a, 'tcx>(&'a LateContext<'tcx>, &'a DerefTy<'tcx>);
 363 impl fmt::Display for DerefTyDisplay<'_, '_> {
 364     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 365         use std::fmt::Write;
 366         match self.1 {
 367             DerefTy::Str => f.write_str("str"),
 368             DerefTy::Path => f.write_str("Path"),
 369             DerefTy::Slice(hir_ty, ty) => {
 370                 f.write_char('[')?;
 371                 match hir_ty.and_then(|s| snippet_opt(self.0, s)) {
 372                     Some(s) => f.write_str(&s)?,
 373                     None => ty.fmt(f)?,
 374                 }
 375                 f.write_char(']')
 376             },
 377         }
 378     }
 379 }
 380
 381 enum DerefTy<'tcx> {
 382     Str,
 383     Path,
 384     Slice(Option<Span>, Ty<'tcx>),
 385 }
 386 impl<'tcx> DerefTy<'tcx> {
 387     fn argless_str(&self) -> &'static str {
 388         match *self {
 389             Self::Str => "str",
 390             Self::Path => "Path",
 391             Self::Slice(..) => "[_]",
 392         }
 393     }
 394
 395     fn display<'a>(&'a self, cx: &'a LateContext<'tcx>) -> DerefTyDisplay<'a, 'tcx> {
 396         DerefTyDisplay(cx, self)
 397     }
 398 }
 399
 400 fn check_fn_args<'cx, 'tcx: 'cx>(
 401     cx: &'cx LateContext<'tcx>,
 402     tys: &'tcx [Ty<'tcx>],
 403     hir_tys: &'tcx [hir::Ty<'tcx>],
 404     params: &'tcx [Param<'tcx>],
 405 ) -> impl Iterator<Item = PtrArg<'tcx>> + 'cx {
 406     tys.iter()
 407         .zip(hir_tys.iter())
 408         .enumerate()
 409         .filter_map(|(i, (ty, hir_ty))| {
 410             if_chain! {
 411                 if let ty::Ref(_, ty, mutability) = *ty.kind();
 412                 if let ty::Adt(adt, substs) = *ty.kind();
 413
 414                 if let TyKind::Rptr(lt, ref ty) = hir_ty.kind;
 415                 if let TyKind::Path(QPath::Resolved(None, path)) = ty.ty.kind;
 416
 417                 // Check that the name as typed matches the actual name of the type.
 418                 // e.g. `fn foo(_: &Foo)` shouldn't trigger the lint when `Foo` is an alias for `Vec`
 419                 if let [.., name] = path.segments;
 420                 if cx.tcx.item_name(adt.did()) == name.ident.name;
 421
 422                 if !is_lint_allowed(cx, PTR_ARG, hir_ty.hir_id);
 423                 if params.get(i).map_or(true, |p| !is_lint_allowed(cx, PTR_ARG, p.hir_id));
 424
 425                 then {
 426                     let (method_renames, deref_ty) = match cx.tcx.get_diagnostic_name(adt.did()) {
 427                         Some(sym::Vec) => (
 428                             [("clone", ".to_owned()")].as_slice(),
 429                             DerefTy::Slice(
 430                                 name.args
 431                                     .and_then(|args| args.args.first())
 432                                     .and_then(|arg| if let GenericArg::Type(ty) = arg {
 433                                         Some(ty.span)
 434                                     } else {
 435                                         None
 436                                     }),
 437                                 substs.type_at(0),
 438                             ),
 439                         ),
 440                         Some(sym::String) => (
 441                             [("clone", ".to_owned()"), ("as_str", "")].as_slice(),
 442                             DerefTy::Str,
 443                         ),
 444                         Some(sym::PathBuf) => (
 445                             [("clone", ".to_path_buf()"), ("as_path", "")].as_slice(),
 446                             DerefTy::Path,
 447                         ),
 448                         Some(sym::Cow) if mutability == Mutability::Not => {
 449                             let ty_name = name.args
 450                                 .and_then(|args| {
 451                                     args.args.iter().find_map(|a| match a {
 452                                         GenericArg::Type(x) => Some(x),
 453                                         _ => None,
 454                                     })
 455                                 })
 456                                 .and_then(|arg| snippet_opt(cx, arg.span))
 457                                 .unwrap_or_else(|| substs.type_at(1).to_string());
 458                             span_lint_and_sugg(
 459                                 cx,
 460                                 PTR_ARG,
 461                                 hir_ty.span,
 462                                 "using a reference to `Cow` is not recommended",
 463                                 "change this to",
 464                                 format!("&{}{}", mutability.prefix_str(), ty_name),
 465                                 Applicability::Unspecified,
 466                             );
 467                             return None;
 468                         },
 469                         _ => return None,
 470                     };
 471                     return Some(PtrArg {
 472                         idx: i,
 473                         span: hir_ty.span,
 474                         ty_did: adt.did(),
 475                         ty_name: name.ident.name,
 476                         method_renames,
 477                         ref_prefix: RefPrefix {
 478                             lt: lt.name,
 479                             mutability,
 480                         },
 481                         deref_ty,
 482                     });
 483                 }
 484             }
 485             None
 486         })
 487 }
 488
 489 fn check_mut_from_ref<'tcx>(cx: &LateContext<'tcx>, sig: &FnSig<'_>, body: Option<&'tcx Body<'_>>) {
 490     if let FnRetTy::Return(ty) = sig.decl.output
 491         && let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty)
 492     {
 493         let args: Option<Vec<_>> = sig
 494             .decl
 495             .inputs
 496             .iter()
 497             .filter_map(get_rptr_lm)
 498             .filter(|&(lt, _, _)| lt.name == out.name)
 499             .map(|(_, mutability, span)| (mutability == Mutability::Not).then(|| span))
 500             .collect();
 501         if let Some(args) = args
 502             && !args.is_empty()
 503             && body.map_or(true, |body| {
 504                 sig.header.unsafety == Unsafety::Unsafe || contains_unsafe_block(cx, &body.value)
 505             })
 506         {
 507             span_lint_and_then(
 508                 cx,
 509                 MUT_FROM_REF,
 510                 ty.span,
 511                 "mutable borrow from immutable input(s)",
 512                 |diag| {
 513                     let ms = MultiSpan::from_spans(args);
 514                     diag.span_note(ms, "immutable borrow here");
 515                 },
 516             );
 517         }
 518     }
 519 }
 520
 521 #[expect(clippy::too_many_lines)]
 522 fn check_ptr_arg_usage<'tcx>(cx: &LateContext<'tcx>, body: &'tcx Body<'_>, args: &[PtrArg<'tcx>]) -> Vec<PtrArgResult> {
 523     struct V<'cx, 'tcx> {
 524         cx: &'cx LateContext<'tcx>,
 525         /// Map from a local id to which argument it came from (index into `Self::args` and
 526         /// `Self::results`)
 527         bindings: HirIdMap<usize>,
 528         /// The arguments being checked.
 529         args: &'cx [PtrArg<'tcx>],
 530         /// The results for each argument (len should match args.len)
 531         results: Vec<PtrArgResult>,
 532         /// The number of arguments which can't be linted. Used to return early.
 533         skip_count: usize,
 534     }
 535     impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
 536         type NestedFilter = nested_filter::OnlyBodies;
 537         fn nested_visit_map(&mut self) -> Self::Map {
 538             self.cx.tcx.hir()
 539         }
 540
 541         fn visit_anon_const(&mut self, _: &'tcx AnonConst) {}
 542
 543         fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
 544             if self.skip_count == self.args.len() {
 545                 return;
 546             }
 547
 548             // Check if this is local we care about
 549             let args_idx = match path_to_local(e).and_then(|id| self.bindings.get(&id)) {
 550                 Some(&i) => i,
 551                 None => return walk_expr(self, e),
 552             };
 553             let args = &self.args[args_idx];
 554             let result = &mut self.results[args_idx];
 555
 556             // Helper function to handle early returns.
 557             let mut set_skip_flag = || {
 558                 if !result.skip {
 559                     self.skip_count += 1;
 560                 }
 561                 result.skip = true;
 562             };
 563
 564             match get_expr_use_or_unification_node(self.cx.tcx, e) {
 565                 Some((Node::Stmt(_), _)) => (),
 566                 Some((Node::Local(l), _)) => {
 567                     // Only trace simple bindings. e.g `let x = y;`
 568                     if let PatKind::Binding(BindingAnnotation::Unannotated, id, _, None) = l.pat.kind {
 569                         self.bindings.insert(id, args_idx);
 570                     } else {
 571                         set_skip_flag();
 572                     }
 573                 },
 574                 Some((Node::Expr(e), child_id)) => match e.kind {
 575                     ExprKind::Call(f, expr_args) => {
 576                         let i = expr_args.iter().position(|arg| arg.hir_id == child_id).unwrap_or(0);
 577                         if expr_sig(self.cx, f)
 578                             .map(|sig| sig.input(i).skip_binder().peel_refs())
 579                             .map_or(true, |ty| match *ty.kind() {
 580                                 ty::Param(_) => true,
 581                                 ty::Adt(def, _) => def.did() == args.ty_did,
 582                                 _ => false,
 583                             })
 584                         {
 585                             // Passed to a function taking the non-dereferenced type.
 586                             set_skip_flag();
 587                         }
 588                     },
 589                     ExprKind::MethodCall(name, expr_args @ [self_arg, ..], _) => {
 590                         let i = expr_args.iter().position(|arg| arg.hir_id == child_id).unwrap_or(0);
 591                         if i == 0 {
 592                             // Check if the method can be renamed.
 593                             let name = name.ident.as_str();
 594                             if let Some((_, replacement)) = args.method_renames.iter().find(|&&(x, _)| x == name) {
 595                                 result.replacements.push(PtrArgReplacement {
 596                                     expr_span: e.span,
 597                                     self_span: self_arg.span,
 598                                     replacement,
 599                                 });
 600                                 return;
 601                             }
 602                         }
 603
 604                         let id = if let Some(x) = self.cx.typeck_results().type_dependent_def_id(e.hir_id) {
 605                             x
 606                         } else {
 607                             set_skip_flag();
 608                             return;
 609                         };
 610
 611                         match *self.cx.tcx.fn_sig(id).skip_binder().inputs()[i].peel_refs().kind() {
 612                             ty::Param(_) => {
 613                                 set_skip_flag();
 614                             },
 615                             // If the types match check for methods which exist on both types. e.g. `Vec::len` and
 616                             // `slice::len`
 617                             ty::Adt(def, _) if def.did() == args.ty_did => {
 618                                 set_skip_flag();
 619                             },
 620                             _ => (),
 621                         }
 622                     },
 623                     // Indexing is fine for currently supported types.
 624                     ExprKind::Index(e, _) if e.hir_id == child_id => (),
 625                     _ => set_skip_flag(),
 626                 },
 627                 _ => set_skip_flag(),
 628             }
 629         }
 630     }
 631
 632     let mut skip_count = 0;
 633     let mut results = args.iter().map(|_| PtrArgResult::default()).collect::<Vec<_>>();
 634     let mut v = V {
 635         cx,
 636         bindings: args
 637             .iter()
 638             .enumerate()
 639             .filter_map(|(i, arg)| {
 640                 let param = &body.params[arg.idx];
 641                 match param.pat.kind {
 642                     PatKind::Binding(BindingAnnotation::Unannotated, id, _, None)
 643                         if !is_lint_allowed(cx, PTR_ARG, param.hir_id) =>
 644                     {
 645                         Some((id, i))
 646                     },
 647                     _ => {
 648                         skip_count += 1;
 649                         results[i].skip = true;
 650                         None
 651                     },
 652                 }
 653             })
 654             .collect(),
 655         args,
 656         results,
 657         skip_count,
 658     };
 659     v.visit_expr(&body.value);
 660     v.results
 661 }
 662
 663 fn get_rptr_lm<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
 664     if let TyKind::Rptr(ref lt, ref m) = ty.kind {
 665         Some((lt, m.mutbl, ty.span))
 666     } else {
 667         None
 668     }
 669 }
 670
 671 fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 672     if let ExprKind::Call(pathexp, []) = expr.kind {
 673         path_def_id(cx, pathexp).map_or(false, |id| {
 674             matches!(cx.tcx.get_diagnostic_name(id), Some(sym::ptr_null | sym::ptr_null_mut))
 675         })
 676     } else {
 677         false
 678     }
 679 }