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::ptr::get_spans;
   5 use clippy_utils::source::snippet_opt;
   6 use clippy_utils::ty::walk_ptrs_hir_ty;
   7 use clippy_utils::{expr_path_res, is_lint_allowed, match_any_diagnostic_items, paths};
   8 use if_chain::if_chain;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::def::Res;
  11 use rustc_hir::{
  12     BinOpKind, BodyId, Expr, ExprKind, FnDecl, FnRetTy, GenericArg, Impl, ImplItem, ImplItemKind, Item, ItemKind,
  13     Lifetime, MutTy, Mutability, Node, PathSegment, QPath, TraitFn, TraitItem, TraitItemKind, Ty, TyKind,
  14 };
  15 use rustc_lint::{LateContext, LateLintPass};
  16 use rustc_session::{declare_lint_pass, declare_tool_lint};
  17 use rustc_span::source_map::Span;
  18 use rustc_span::symbol::Symbol;
  19 use rustc_span::{sym, MultiSpan};
  20 use std::borrow::Cow;
  21
  22 declare_clippy_lint! {
  23     /// ### What it does
  24     /// This lint checks for function arguments of type `&String`
  25     /// or `&Vec` unless the references are mutable. It will also suggest you
  26     /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
  27     /// calls.
  28     ///
  29     /// ### Why is this bad?
  30     /// Requiring the argument to be of the specific size
  31     /// makes the function less useful for no benefit; slices in the form of `&[T]`
  32     /// or `&str` usually suffice and can be obtained from other types, too.
  33     ///
  34     /// ### Known problems
  35     /// The lint does not follow data. So if you have an
  36     /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
  37     /// changing that `.clone()` to `.to_owned()`.
  38     ///
  39     /// Other functions called from this function taking a `&String` or `&Vec`
  40     /// argument may also fail to compile if you change the argument. Applying
  41     /// this lint on them will fix the problem, but they may be in other crates.
  42     ///
  43     /// One notable example of a function that may cause issues, and which cannot
  44     /// easily be changed due to being in the standard library is `Vec::contains`.
  45     /// when called on a `Vec<Vec<T>>`. If a `&Vec` is passed to that method then
  46     /// it will compile, but if a `&[T]` is passed then it will not compile.
  47     ///
  48     /// ```ignore
  49     /// fn cannot_take_a_slice(v: &Vec<u8>) -> bool {
  50     ///     let vec_of_vecs: Vec<Vec<u8>> = some_other_fn();
  51     ///
  52     ///     vec_of_vecs.contains(v)
  53     /// }
  54     /// ```
  55     ///
  56     /// Also there may be `fn(&Vec)`-typed references pointing to your function.
  57     /// If you have them, you will get a compiler error after applying this lint's
  58     /// suggestions. You then have the choice to undo your changes or change the
  59     /// type of the reference.
  60     ///
  61     /// Note that if the function is part of your public interface, there may be
  62     /// other crates referencing it, of which you may not be aware. Carefully
  63     /// deprecate the function before applying the lint suggestions in this case.
  64     ///
  65     /// ### Example
  66     /// ```ignore
  67     /// // Bad
  68     /// fn foo(&Vec<u32>) { .. }
  69     ///
  70     /// // Good
  71     /// fn foo(&[u32]) { .. }
  72     /// ```
  73     pub PTR_ARG,
  74     style,
  75     "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
  76 }
  77
  78 declare_clippy_lint! {
  79     /// ### What it does
  80     /// This lint checks for equality comparisons with `ptr::null`
  81     ///
  82     /// ### Why is this bad?
  83     /// It's easier and more readable to use the inherent
  84     /// `.is_null()`
  85     /// method instead
  86     ///
  87     /// ### Example
  88     /// ```ignore
  89     /// // Bad
  90     /// if x == ptr::null {
  91     ///     ..
  92     /// }
  93     ///
  94     /// // Good
  95     /// if x.is_null() {
  96     ///     ..
  97     /// }
  98     /// ```
  99     pub CMP_NULL,
 100     style,
 101     "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead"
 102 }
 103
 104 declare_clippy_lint! {
 105     /// ### What it does
 106     /// This lint checks for functions that take immutable
 107     /// references and return mutable ones.
 108     ///
 109     /// ### Why is this bad?
 110     /// This is trivially unsound, as one can create two
 111     /// mutable references from the same (immutable!) source.
 112     /// This [error](https://github.com/rust-lang/rust/issues/39465)
 113     /// actually lead to an interim Rust release 1.15.1.
 114     ///
 115     /// ### Known problems
 116     /// To be on the conservative side, if there's at least one
 117     /// mutable reference with the output lifetime, this lint will not trigger.
 118     /// In practice, this case is unlikely anyway.
 119     ///
 120     /// ### Example
 121     /// ```ignore
 122     /// fn foo(&Foo) -> &mut Bar { .. }
 123     /// ```
 124     pub MUT_FROM_REF,
 125     correctness,
 126     "fns that create mutable refs from immutable ref args"
 127 }
 128
 129 declare_clippy_lint! {
 130     /// ### What it does
 131     /// This lint checks for invalid usages of `ptr::null`.
 132     ///
 133     /// ### Why is this bad?
 134     /// This causes undefined behavior.
 135     ///
 136     /// ### Example
 137     /// ```ignore
 138     /// // Bad. Undefined behavior
 139     /// unsafe { std::slice::from_raw_parts(ptr::null(), 0); }
 140     /// ```
 141     ///
 142     /// ```ignore
 143     /// // Good
 144     /// unsafe { std::slice::from_raw_parts(NonNull::dangling().as_ptr(), 0); }
 145     /// ```
 146     pub INVALID_NULL_PTR_USAGE,
 147     correctness,
 148     "invalid usage of a null pointer, suggesting `NonNull::dangling()` instead"
 149 }
 150
 151 declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF, INVALID_NULL_PTR_USAGE]);
 152
 153 impl<'tcx> LateLintPass<'tcx> for Ptr {
 154     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 155         if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
 156             check_fn(cx, sig.decl, Some(body_id));
 157         }
 158     }
 159
 160     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
 161         if let ImplItemKind::Fn(ref sig, body_id) = item.kind {
 162             let parent_item = cx.tcx.hir().get_parent_item(item.hir_id());
 163             if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
 164                 if let ItemKind::Impl(Impl { of_trait: Some(_), .. }) = it.kind {
 165                     return; // ignore trait impls
 166                 }
 167             }
 168             check_fn(cx, sig.decl, Some(body_id));
 169         }
 170     }
 171
 172     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 173         if let TraitItemKind::Fn(ref sig, ref trait_method) = item.kind {
 174             let body_id = if let TraitFn::Provided(b) = *trait_method {
 175                 Some(b)
 176             } else {
 177                 None
 178             };
 179             check_fn(cx, sig.decl, body_id);
 180         }
 181     }
 182
 183     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 184         if let ExprKind::Binary(ref op, l, r) = expr.kind {
 185             if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(cx, l) || is_null_path(cx, r)) {
 186                 span_lint(
 187                     cx,
 188                     CMP_NULL,
 189                     expr.span,
 190                     "comparing with null is better expressed by the `.is_null()` method",
 191                 );
 192             }
 193         } else {
 194             check_invalid_ptr_usage(cx, expr);
 195         }
 196     }
 197 }
 198
 199 fn check_invalid_ptr_usage<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 200     // (fn_path, arg_indices) - `arg_indices` are the `arg` positions where null would cause U.B.
 201     const INVALID_NULL_PTR_USAGE_TABLE: [(&[&str], &[usize]); 16] = [
 202         (&paths::SLICE_FROM_RAW_PARTS, &[0]),
 203         (&paths::SLICE_FROM_RAW_PARTS_MUT, &[0]),
 204         (&paths::PTR_COPY, &[0, 1]),
 205         (&paths::PTR_COPY_NONOVERLAPPING, &[0, 1]),
 206         (&paths::PTR_READ, &[0]),
 207         (&paths::PTR_READ_UNALIGNED, &[0]),
 208         (&paths::PTR_READ_VOLATILE, &[0]),
 209         (&paths::PTR_REPLACE, &[0]),
 210         (&paths::PTR_SLICE_FROM_RAW_PARTS, &[0]),
 211         (&paths::PTR_SLICE_FROM_RAW_PARTS_MUT, &[0]),
 212         (&paths::PTR_SWAP, &[0, 1]),
 213         (&paths::PTR_SWAP_NONOVERLAPPING, &[0, 1]),
 214         (&paths::PTR_WRITE, &[0]),
 215         (&paths::PTR_WRITE_UNALIGNED, &[0]),
 216         (&paths::PTR_WRITE_VOLATILE, &[0]),
 217         (&paths::PTR_WRITE_BYTES, &[0]),
 218     ];
 219
 220     if_chain! {
 221         if let ExprKind::Call(fun, args) = expr.kind;
 222         if let ExprKind::Path(ref qpath) = fun.kind;
 223         if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
 224         let fun_def_path = cx.get_def_path(fun_def_id).into_iter().map(Symbol::to_ident_string).collect::<Vec<_>>();
 225         if let Some(&(_, arg_indices)) = INVALID_NULL_PTR_USAGE_TABLE
 226             .iter()
 227             .find(|&&(fn_path, _)| fn_path == fun_def_path);
 228         then {
 229             for &arg_idx in arg_indices {
 230                 if let Some(arg) = args.get(arg_idx).filter(|arg| is_null_path(cx, arg)) {
 231                     span_lint_and_sugg(
 232                         cx,
 233                         INVALID_NULL_PTR_USAGE,
 234                         arg.span,
 235                         "pointer must be non-null",
 236                         "change this to",
 237                         "core::ptr::NonNull::dangling().as_ptr()".to_string(),
 238                         Applicability::MachineApplicable,
 239                     );
 240                 }
 241             }
 242         }
 243     }
 244 }
 245
 246 #[allow(clippy::too_many_lines)]
 247 fn check_fn(cx: &LateContext<'_>, decl: &FnDecl<'_>, opt_body_id: Option<BodyId>) {
 248     let body = opt_body_id.map(|id| cx.tcx.hir().body(id));
 249
 250     for (idx, arg) in decl.inputs.iter().enumerate() {
 251         // Honor the allow attribute on parameters. See issue 5644.
 252         if let Some(body) = &body {
 253             if is_lint_allowed(cx, PTR_ARG, body.params[idx].hir_id) {
 254                 continue;
 255             }
 256         }
 257
 258         let (item_name, path) = if_chain! {
 259             if let TyKind::Rptr(_, MutTy { ty, mutbl: Mutability::Not }) = arg.kind;
 260             if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
 261             if let Res::Def(_, did) = path.res;
 262             if let Some(item_name) = cx.tcx.get_diagnostic_name(did);
 263             then {
 264                 (item_name, path)
 265             } else {
 266                 continue
 267             }
 268         };
 269
 270         match item_name {
 271             sym::Vec => {
 272                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
 273                     span_lint_and_then(
 274                         cx,
 275                         PTR_ARG,
 276                         arg.span,
 277                         "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
 278                          with non-Vec-based slices",
 279                         |diag| {
 280                             if let Some(ref snippet) = get_only_generic_arg_snippet(cx, arg) {
 281                                 diag.span_suggestion(
 282                                     arg.span,
 283                                     "change this to",
 284                                     format!("&[{}]", snippet),
 285                                     Applicability::Unspecified,
 286                                 );
 287                             }
 288                             for (clonespan, suggestion) in spans {
 289                                 diag.span_suggestion(
 290                                     clonespan,
 291                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
 292                                         Cow::Owned(format!("change `{}` to", x))
 293                                     }),
 294                                     suggestion.into(),
 295                                     Applicability::Unspecified,
 296                                 );
 297                             }
 298                         },
 299                     );
 300                 }
 301             },
 302             sym::String => {
 303                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
 304                     span_lint_and_then(
 305                         cx,
 306                         PTR_ARG,
 307                         arg.span,
 308                         "writing `&String` instead of `&str` involves a new object where a slice will do",
 309                         |diag| {
 310                             diag.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
 311                             for (clonespan, suggestion) in spans {
 312                                 diag.span_suggestion_short(
 313                                     clonespan,
 314                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
 315                                         Cow::Owned(format!("change `{}` to", x))
 316                                     }),
 317                                     suggestion.into(),
 318                                     Applicability::Unspecified,
 319                                 );
 320                             }
 321                         },
 322                     );
 323                 }
 324             },
 325             sym::PathBuf => {
 326                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_path_buf()"), ("as_path", "")]) {
 327                     span_lint_and_then(
 328                         cx,
 329                         PTR_ARG,
 330                         arg.span,
 331                         "writing `&PathBuf` instead of `&Path` involves a new object where a slice will do",
 332                         |diag| {
 333                             diag.span_suggestion(
 334                                 arg.span,
 335                                 "change this to",
 336                                 "&Path".into(),
 337                                 Applicability::Unspecified,
 338                             );
 339                             for (clonespan, suggestion) in spans {
 340                                 diag.span_suggestion_short(
 341                                     clonespan,
 342                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
 343                                         Cow::Owned(format!("change `{}` to", x))
 344                                     }),
 345                                     suggestion.into(),
 346                                     Applicability::Unspecified,
 347                                 );
 348                             }
 349                         },
 350                     );
 351                 }
 352             },
 353             sym::Cow => {
 354                 if_chain! {
 355                     if let [ref bx] = *path.segments;
 356                     if let Some(params) = bx.args;
 357                     if !params.parenthesized;
 358                     if let Some(inner) = params.args.iter().find_map(|arg| match arg {
 359                         GenericArg::Type(ty) => Some(ty),
 360                         _ => None,
 361                     });
 362                     let replacement = snippet_opt(cx, inner.span);
 363                     if let Some(r) = replacement;
 364                     then {
 365                         span_lint_and_sugg(
 366                             cx,
 367                             PTR_ARG,
 368                             arg.span,
 369                             "using a reference to `Cow` is not recommended",
 370                             "change this to",
 371                             "&".to_owned() + &r,
 372                             Applicability::Unspecified,
 373                         );
 374                     }
 375                 }
 376             },
 377             _ => {},
 378         }
 379     }
 380
 381     if let FnRetTy::Return(ty) = decl.output {
 382         if let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty) {
 383             let mut immutables = vec![];
 384             for (_, ref mutbl, ref argspan) in decl
 385                 .inputs
 386                 .iter()
 387                 .filter_map(get_rptr_lm)
 388                 .filter(|&(lt, _, _)| lt.name == out.name)
 389             {
 390                 if *mutbl == Mutability::Mut {
 391                     return;
 392                 }
 393                 immutables.push(*argspan);
 394             }
 395             if immutables.is_empty() {
 396                 return;
 397             }
 398             span_lint_and_then(
 399                 cx,
 400                 MUT_FROM_REF,
 401                 ty.span,
 402                 "mutable borrow from immutable input(s)",
 403                 |diag| {
 404                     let ms = MultiSpan::from_spans(immutables);
 405                     diag.span_note(ms, "immutable borrow here");
 406                 },
 407             );
 408         }
 409     }
 410 }
 411
 412 fn get_only_generic_arg_snippet(cx: &LateContext<'_>, arg: &Ty<'_>) -> Option<String> {
 413     if_chain! {
 414         if let TyKind::Path(QPath::Resolved(_, path)) = walk_ptrs_hir_ty(arg).kind;
 415         if let Some(&PathSegment{args: Some(parameters), ..}) = path.segments.last();
 416         let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
 417             GenericArg::Type(ty) => Some(ty),
 418             _ => None,
 419         }).collect();
 420         if types.len() == 1;
 421         then {
 422             snippet_opt(cx, types[0].span)
 423         } else {
 424             None
 425         }
 426     }
 427 }
 428
 429 fn get_rptr_lm<'tcx>(ty: &'tcx Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
 430     if let TyKind::Rptr(ref lt, ref m) = ty.kind {
 431         Some((lt, m.mutbl, ty.span))
 432     } else {
 433         None
 434     }
 435 }
 436
 437 fn is_null_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 438     if let ExprKind::Call(pathexp, []) = expr.kind {
 439         expr_path_res(cx, pathexp).opt_def_id().map_or(false, |id| {
 440             match_any_diagnostic_items(cx, id, &[sym::ptr_null, sym::ptr_null_mut]).is_some()
 441         })
 442     } else {
 443         false
 444     }
 445 }