clippy_lints/src/unnecessary_sort_by.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::sugg::Sugg;
   3 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Closure, Expr, ExprKind, Mutability, Param, Pat, PatKind, Path, PathSegment, QPath};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::ty::{self, subst::GenericArgKind};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::sym;
  11 use rustc_span::symbol::Ident;
  12 use std::iter;
  13
  14 declare_clippy_lint! {
  15     /// ### What it does
  16     /// Detects uses of `Vec::sort_by` passing in a closure
  17     /// which compares the two arguments, either directly or indirectly.
  18     ///
  19     /// ### Why is this bad?
  20     /// It is more clear to use `Vec::sort_by_key` (or `Vec::sort` if
  21     /// possible) than to use `Vec::sort_by` and a more complicated
  22     /// closure.
  23     ///
  24     /// ### Known problems
  25     /// If the suggested `Vec::sort_by_key` uses Reverse and it isn't already
  26     /// imported by a use statement, then it will need to be added manually.
  27     ///
  28     /// ### Example
  29     /// ```rust
  30     /// # struct A;
  31     /// # impl A { fn foo(&self) {} }
  32     /// # let mut vec: Vec<A> = Vec::new();
  33     /// vec.sort_by(|a, b| a.foo().cmp(&b.foo()));
  34     /// ```
  35     /// Use instead:
  36     /// ```rust
  37     /// # struct A;
  38     /// # impl A { fn foo(&self) {} }
  39     /// # let mut vec: Vec<A> = Vec::new();
  40     /// vec.sort_by_key(|a| a.foo());
  41     /// ```
  42     #[clippy::version = "1.46.0"]
  43     pub UNNECESSARY_SORT_BY,
  44     complexity,
  45     "Use of `Vec::sort_by` when `Vec::sort_by_key` or `Vec::sort` would be clearer"
  46 }
  47
  48 declare_lint_pass!(UnnecessarySortBy => [UNNECESSARY_SORT_BY]);
  49
  50 enum LintTrigger {
  51     Sort(SortDetection),
  52     SortByKey(SortByKeyDetection),
  53 }
  54
  55 struct SortDetection {
  56     vec_name: String,
  57     unstable: bool,
  58 }
  59
  60 struct SortByKeyDetection {
  61     vec_name: String,
  62     closure_arg: String,
  63     closure_body: String,
  64     reverse: bool,
  65     unstable: bool,
  66 }
  67
  68 /// Detect if the two expressions are mirrored (identical, except one
  69 /// contains a and the other replaces it with b)
  70 fn mirrored_exprs(a_expr: &Expr<'_>, a_ident: &Ident, b_expr: &Expr<'_>, b_ident: &Ident) -> bool {
  71     match (&a_expr.kind, &b_expr.kind) {
  72         // Two boxes with mirrored contents
  73         (ExprKind::Box(left_expr), ExprKind::Box(right_expr)) => {
  74             mirrored_exprs(left_expr, a_ident, right_expr, b_ident)
  75         },
  76         // Two arrays with mirrored contents
  77         (ExprKind::Array(left_exprs), ExprKind::Array(right_exprs)) => {
  78             iter::zip(*left_exprs, *right_exprs).all(|(left, right)| mirrored_exprs(left, a_ident, right, b_ident))
  79         },
  80         // The two exprs are function calls.
  81         // Check to see that the function itself and its arguments are mirrored
  82         (ExprKind::Call(left_expr, left_args), ExprKind::Call(right_expr, right_args)) => {
  83             mirrored_exprs(left_expr, a_ident, right_expr, b_ident)
  84                 && iter::zip(*left_args, *right_args).all(|(left, right)| mirrored_exprs(left, a_ident, right, b_ident))
  85         },
  86         // The two exprs are method calls.
  87         // Check to see that the function is the same and the arguments are mirrored
  88         // This is enough because the receiver of the method is listed in the arguments
  89         (ExprKind::MethodCall(left_segment, left_args, _), ExprKind::MethodCall(right_segment, right_args, _)) => {
  90             left_segment.ident == right_segment.ident
  91                 && iter::zip(*left_args, *right_args).all(|(left, right)| mirrored_exprs(left, a_ident, right, b_ident))
  92         },
  93         // Two tuples with mirrored contents
  94         (ExprKind::Tup(left_exprs), ExprKind::Tup(right_exprs)) => {
  95             iter::zip(*left_exprs, *right_exprs).all(|(left, right)| mirrored_exprs(left, a_ident, right, b_ident))
  96         },
  97         // Two binary ops, which are the same operation and which have mirrored arguments
  98         (ExprKind::Binary(left_op, left_left, left_right), ExprKind::Binary(right_op, right_left, right_right)) => {
  99             left_op.node == right_op.node
 100                 && mirrored_exprs(left_left, a_ident, right_left, b_ident)
 101                 && mirrored_exprs(left_right, a_ident, right_right, b_ident)
 102         },
 103         // Two unary ops, which are the same operation and which have the same argument
 104         (ExprKind::Unary(left_op, left_expr), ExprKind::Unary(right_op, right_expr)) => {
 105             left_op == right_op && mirrored_exprs(left_expr, a_ident, right_expr, b_ident)
 106         },
 107         // The two exprs are literals of some kind
 108         (ExprKind::Lit(left_lit), ExprKind::Lit(right_lit)) => left_lit.node == right_lit.node,
 109         (ExprKind::Cast(left, _), ExprKind::Cast(right, _)) => mirrored_exprs(left, a_ident, right, b_ident),
 110         (ExprKind::DropTemps(left_block), ExprKind::DropTemps(right_block)) => {
 111             mirrored_exprs(left_block, a_ident, right_block, b_ident)
 112         },
 113         (ExprKind::Field(left_expr, left_ident), ExprKind::Field(right_expr, right_ident)) => {
 114             left_ident.name == right_ident.name && mirrored_exprs(left_expr, a_ident, right_expr, right_ident)
 115         },
 116         // Two paths: either one is a and the other is b, or they're identical to each other
 117         (
 118             ExprKind::Path(QPath::Resolved(
 119                 _,
 120                 Path {
 121                     segments: left_segments,
 122                     ..
 123                 },
 124             )),
 125             ExprKind::Path(QPath::Resolved(
 126                 _,
 127                 Path {
 128                     segments: right_segments,
 129                     ..
 130                 },
 131             )),
 132         ) => {
 133             (iter::zip(*left_segments, *right_segments).all(|(left, right)| left.ident == right.ident)
 134                 && left_segments
 135                     .iter()
 136                     .all(|seg| &seg.ident != a_ident && &seg.ident != b_ident))
 137                 || (left_segments.len() == 1
 138                     && &left_segments[0].ident == a_ident
 139                     && right_segments.len() == 1
 140                     && &right_segments[0].ident == b_ident)
 141         },
 142         // Matching expressions, but one or both is borrowed
 143         (
 144             ExprKind::AddrOf(left_kind, Mutability::Not, left_expr),
 145             ExprKind::AddrOf(right_kind, Mutability::Not, right_expr),
 146         ) => left_kind == right_kind && mirrored_exprs(left_expr, a_ident, right_expr, b_ident),
 147         (_, ExprKind::AddrOf(_, Mutability::Not, right_expr)) => mirrored_exprs(a_expr, a_ident, right_expr, b_ident),
 148         (ExprKind::AddrOf(_, Mutability::Not, left_expr), _) => mirrored_exprs(left_expr, a_ident, b_expr, b_ident),
 149         _ => false,
 150     }
 151 }
 152
 153 fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
 154     if_chain! {
 155         if let ExprKind::MethodCall(name_ident, args, _) = &expr.kind;
 156         if let name = name_ident.ident.name.to_ident_string();
 157         if name == "sort_by" || name == "sort_unstable_by";
 158         if let [vec, Expr { kind: ExprKind::Closure(Closure { body: closure_body_id, .. }), .. }] = args;
 159         if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(vec), sym::Vec);
 160         if let closure_body = cx.tcx.hir().body(*closure_body_id);
 161         if let &[
 162             Param { pat: Pat { kind: PatKind::Binding(_, _, left_ident, _), .. }, ..},
 163             Param { pat: Pat { kind: PatKind::Binding(_, _, right_ident, _), .. }, .. }
 164         ] = &closure_body.params;
 165         if let ExprKind::MethodCall(method_path, [ref left_expr, ref right_expr], _) = &closure_body.value.kind;
 166         if method_path.ident.name == sym::cmp;
 167         then {
 168             let (closure_body, closure_arg, reverse) = if mirrored_exprs(
 169                 left_expr,
 170                 left_ident,
 171                 right_expr,
 172                 right_ident
 173             ) {
 174                 (Sugg::hir(cx, left_expr, "..").to_string(), left_ident.name.to_string(), false)
 175             } else if mirrored_exprs(left_expr, right_ident, right_expr, left_ident) {
 176                 (Sugg::hir(cx, left_expr, "..").to_string(), right_ident.name.to_string(), true)
 177             } else {
 178                 return None;
 179             };
 180             let vec_name = Sugg::hir(cx, &args[0], "..").to_string();
 181             let unstable = name == "sort_unstable_by";
 182
 183             if_chain! {
 184             if let ExprKind::Path(QPath::Resolved(_, Path {
 185                 segments: [PathSegment { ident: left_name, .. }], ..
 186             })) = &left_expr.kind;
 187             if left_name == left_ident;
 188             if cx.tcx.get_diagnostic_item(sym::Ord).map_or(false, |id| {
 189                 implements_trait(cx, cx.typeck_results().expr_ty(left_expr), id, &[])
 190             });
 191                 then {
 192                     return Some(LintTrigger::Sort(SortDetection { vec_name, unstable }));
 193                 }
 194             }
 195
 196             if !expr_borrows(cx, left_expr) {
 197                 return Some(LintTrigger::SortByKey(SortByKeyDetection {
 198                     vec_name,
 199                     closure_arg,
 200                     closure_body,
 201                     reverse,
 202                     unstable,
 203                 }));
 204             }
 205         }
 206     }
 207
 208     None
 209 }
 210
 211 fn expr_borrows(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 212     let ty = cx.typeck_results().expr_ty(expr);
 213     matches!(ty.kind(), ty::Ref(..)) || ty.walk().any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(_)))
 214 }
 215
 216 impl LateLintPass<'_> for UnnecessarySortBy {
 217     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
 218         match detect_lint(cx, expr) {
 219             Some(LintTrigger::SortByKey(trigger)) => span_lint_and_sugg(
 220                 cx,
 221                 UNNECESSARY_SORT_BY,
 222                 expr.span,
 223                 "use Vec::sort_by_key here instead",
 224                 "try",
 225                 format!(
 226                     "{}.sort{}_by_key(|{}| {})",
 227                     trigger.vec_name,
 228                     if trigger.unstable { "_unstable" } else { "" },
 229                     trigger.closure_arg,
 230                     if trigger.reverse {
 231                         format!("std::cmp::Reverse({})", trigger.closure_body)
 232                     } else {
 233                         trigger.closure_body.to_string()
 234                     },
 235                 ),
 236                 if trigger.reverse {
 237                     Applicability::MaybeIncorrect
 238                 } else {
 239                     Applicability::MachineApplicable
 240                 },
 241             ),
 242             Some(LintTrigger::Sort(trigger)) => span_lint_and_sugg(
 243                 cx,
 244                 UNNECESSARY_SORT_BY,
 245                 expr.span,
 246                 "use Vec::sort here instead",
 247                 "try",
 248                 format!(
 249                     "{}.sort{}()",
 250                     trigger.vec_name,
 251                     if trigger.unstable { "_unstable" } else { "" },
 252                 ),
 253                 Applicability::MachineApplicable,
 254             ),
 255             None => {},
 256         }
 257     }
 258 }