clippy_lints/src/ptr.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 //! Checks for usage of  `&Vec[_]` and `&String`.
  11
  12 use crate::rustc::hir::QPath;
  13 use crate::rustc::hir::*;
  14 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  15 use crate::rustc::ty;
  16 use crate::rustc::{declare_tool_lint, lint_array};
  17 use crate::rustc_errors::Applicability;
  18 use crate::syntax::ast::NodeId;
  19 use crate::syntax::source_map::Span;
  20 use crate::syntax_pos::MultiSpan;
  21 use crate::utils::ptr::get_spans;
  22 use crate::utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty};
  23 use if_chain::if_chain;
  24 use std::borrow::Cow;
  25
  26 /// **What it does:** This lint checks for function arguments of type `&String`
  27 /// or `&Vec` unless the references are mutable. It will also suggest you
  28 /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
  29 /// calls.
  30 ///
  31 /// **Why is this bad?** Requiring the argument to be of the specific size
  32 /// makes the function less useful for no benefit; slices in the form of `&[T]`
  33 /// or `&str` usually suffice and can be obtained from other types, too.
  34 ///
  35 /// **Known problems:** 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 /// Also there may be `fn(&Vec)`-typed references pointing to your function.
  44 /// If you have them, you will get a compiler error after applying this lint's
  45 /// suggestions. You then have the choice to undo your changes or change the
  46 /// type of the reference.
  47 ///
  48 /// Note that if the function is part of your public interface, there may be
  49 /// other crates referencing it you may not be aware. Carefully deprecate the
  50 /// function before applying the lint suggestions in this case.
  51 ///
  52 /// **Example:**
  53 /// ```rust
  54 /// fn foo(&Vec<u32>) { .. }
  55 /// ```
  56 declare_clippy_lint! {
  57     pub PTR_ARG,
  58     style,
  59     "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
  60 }
  61
  62 /// **What it does:** This lint checks for equality comparisons with `ptr::null`
  63 ///
  64 /// **Why is this bad?** It's easier and more readable to use the inherent
  65 /// `.is_null()`
  66 /// method instead
  67 ///
  68 /// **Known problems:** None.
  69 ///
  70 /// **Example:**
  71 /// ```rust
  72 /// if x == ptr::null {
  73 ///     ..
  74 /// }
  75 /// ```
  76 declare_clippy_lint! {
  77     pub CMP_NULL,
  78     style,
  79     "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
  80 }
  81
  82 /// **What it does:** This lint checks for functions that take immutable
  83 /// references and return
  84 /// mutable ones.
  85 ///
  86 /// **Why is this bad?** This is trivially unsound, as one can create two
  87 /// mutable references
  88 /// from the same (immutable!) source. This
  89 /// [error](https://github.com/rust-lang/rust/issues/39465)
  90 /// actually lead to an interim Rust release 1.15.1.
  91 ///
  92 /// **Known problems:** To be on the conservative side, if there's at least one
  93 /// mutable reference
  94 /// with the output lifetime, this lint will not trigger. In practice, this
  95 /// case is unlikely anyway.
  96 ///
  97 /// **Example:**
  98 /// ```rust
  99 /// fn foo(&Foo) -> &mut Bar { .. }
 100 /// ```
 101 declare_clippy_lint! {
 102     pub MUT_FROM_REF,
 103     correctness,
 104     "fns that create mutable refs from immutable ref args"
 105 }
 106
 107 #[derive(Copy, Clone)]
 108 pub struct PointerPass;
 109
 110 impl LintPass for PointerPass {
 111     fn get_lints(&self) -> LintArray {
 112         lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF)
 113     }
 114 }
 115
 116 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass {
 117     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
 118         if let ItemKind::Fn(ref decl, _, _, body_id) = item.node {
 119             check_fn(cx, decl, item.id, Some(body_id));
 120         }
 121     }
 122
 123     fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
 124         if let ImplItemKind::Method(ref sig, body_id) = item.node {
 125             if let Some(Node::Item(it)) = cx.tcx.hir().find(cx.tcx.hir().get_parent(item.id)) {
 126                 if let ItemKind::Impl(_, _, _, _, Some(_), _, _) = it.node {
 127                     return; // ignore trait impls
 128                 }
 129             }
 130             check_fn(cx, &sig.decl, item.id, Some(body_id));
 131         }
 132     }
 133
 134     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
 135         if let TraitItemKind::Method(ref sig, ref trait_method) = item.node {
 136             let body_id = if let TraitMethod::Provided(b) = *trait_method {
 137                 Some(b)
 138             } else {
 139                 None
 140             };
 141             check_fn(cx, &sig.decl, item.id, body_id);
 142         }
 143     }
 144
 145     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 146         if let ExprKind::Binary(ref op, ref l, ref r) = expr.node {
 147             if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
 148                 span_lint(
 149                     cx,
 150                     CMP_NULL,
 151                     expr.span,
 152                     "Comparing with null is better expressed by the .is_null() method",
 153                 );
 154             }
 155         }
 156     }
 157 }
 158
 159 fn check_fn(cx: &LateContext<'_, '_>, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option<BodyId>) {
 160     let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
 161     let sig = cx.tcx.fn_sig(fn_def_id);
 162     let fn_ty = sig.skip_binder();
 163
 164     for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
 165         if let ty::Ref(_, ty, MutImmutable) = ty.sty {
 166             if match_type(cx, ty, &paths::VEC) {
 167                 let mut ty_snippet = None;
 168                 if_chain! {
 169                     if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node;
 170                     if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
 171                     then {
 172                         let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
 173                             GenericArg::Type(ty) => Some(ty),
 174                             _ => None,
 175                         }).collect();
 176                         if types.len() == 1 {
 177                             ty_snippet = snippet_opt(cx, types[0].span);
 178                         }
 179                     }
 180                 };
 181                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
 182                     span_lint_and_then(
 183                         cx,
 184                         PTR_ARG,
 185                         arg.span,
 186                         "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
 187                          with non-Vec-based slices.",
 188                         |db| {
 189                             if let Some(ref snippet) = ty_snippet {
 190                                 db.span_suggestion_with_applicability(
 191                                     arg.span,
 192                                     "change this to",
 193                                     format!("&[{}]", snippet),
 194                                     Applicability::Unspecified,
 195                                 );
 196                             }
 197                             for (clonespan, suggestion) in spans {
 198                                 db.span_suggestion_with_applicability(
 199                                     clonespan,
 200                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
 201                                         Cow::Owned(format!("change `{}` to", x))
 202                                     }),
 203                                     suggestion.into(),
 204                                     Applicability::Unspecified,
 205                                 );
 206                             }
 207                         },
 208                     );
 209                 }
 210             } else if match_type(cx, ty, &paths::STRING) {
 211                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
 212                     span_lint_and_then(
 213                         cx,
 214                         PTR_ARG,
 215                         arg.span,
 216                         "writing `&String` instead of `&str` involves a new object where a slice will do.",
 217                         |db| {
 218                             db.span_suggestion_with_applicability(
 219                                 arg.span,
 220                                 "change this to",
 221                                 "&str".into(),
 222                                 Applicability::Unspecified,
 223                             );
 224                             for (clonespan, suggestion) in spans {
 225                                 db.span_suggestion_short_with_applicability(
 226                                     clonespan,
 227                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
 228                                         Cow::Owned(format!("change `{}` to", x))
 229                                     }),
 230                                     suggestion.into(),
 231                                     Applicability::Unspecified,
 232                                 );
 233                             }
 234                         },
 235                     );
 236                 }
 237             } else if match_type(cx, ty, &paths::COW) {
 238                 if_chain! {
 239                     if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.node;
 240                     if let TyKind::Path(ref path) = ty.node;
 241                     if let QPath::Resolved(None, ref pp) = *path;
 242                     if let [ref bx] = *pp.segments;
 243                     if let Some(ref params) = bx.args;
 244                     if !params.parenthesized;
 245                     if let Some(inner) = params.args.iter().find_map(|arg| match arg {
 246                         GenericArg::Type(ty) => Some(ty),
 247                         GenericArg::Lifetime(_) => None,
 248                     });
 249                     then {
 250                         let replacement = snippet_opt(cx, inner.span);
 251                         if let Some(r) = replacement {
 252                             span_lint_and_then(
 253                                 cx,
 254                                 PTR_ARG,
 255                                 arg.span,
 256                                 "using a reference to `Cow` is not recommended.",
 257                                 |db| {
 258                                     db.span_suggestion_with_applicability(
 259                                         arg.span,
 260                                         "change this to",
 261                                         "&".to_owned() + &r,
 262                                         Applicability::Unspecified,
 263                                     );
 264                                 },
 265                             );
 266                         }
 267                     }
 268                 }
 269             }
 270         }
 271     }
 272
 273     if let FunctionRetTy::Return(ref ty) = decl.output {
 274         if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
 275             let mut immutables = vec![];
 276             for (_, ref mutbl, ref argspan) in decl
 277                 .inputs
 278                 .iter()
 279                 .filter_map(|ty| get_rptr_lm(ty))
 280                 .filter(|&(lt, _, _)| lt.name == out.name)
 281             {
 282                 if *mutbl == MutMutable {
 283                     return;
 284                 }
 285                 immutables.push(*argspan);
 286             }
 287             if immutables.is_empty() {
 288                 return;
 289             }
 290             span_lint_and_then(
 291                 cx,
 292                 MUT_FROM_REF,
 293                 ty.span,
 294                 "mutable borrow from immutable input(s)",
 295                 |db| {
 296                     let ms = MultiSpan::from_spans(immutables);
 297                     db.span_note(ms, "immutable borrow here");
 298                 },
 299             );
 300         }
 301     }
 302 }
 303
 304 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
 305     if let TyKind::Rptr(ref lt, ref m) = ty.node {
 306         Some((lt, m.mutbl, ty.span))
 307     } else {
 308         None
 309     }
 310 }
 311
 312 fn is_null_path(expr: &Expr) -> bool {
 313     if let ExprKind::Call(ref pathexp, ref args) = expr.node {
 314         if args.is_empty() {
 315             if let ExprKind::Path(ref path) = pathexp.node {
 316                 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);
 317             }
 318         }
 319     }
 320     false
 321 }