src/tools/clippy/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::{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     pub UNNECESSARY_SORT_BY,
  43     complexity,
  44     "Use of `Vec::sort_by` when `Vec::sort_by_key` or `Vec::sort` would be clearer"
  45 }
  46
  47 declare_lint_pass!(UnnecessarySortBy => [UNNECESSARY_SORT_BY]);
  48
  49 enum LintTrigger {
  50     Sort(SortDetection),
  51     SortByKey(SortByKeyDetection),
  52 }
  53
  54 struct SortDetection {
  55     vec_name: String,
  56     unstable: bool,
  57 }
  58
  59 struct SortByKeyDetection {
  60     vec_name: String,
  61     closure_arg: String,
  62     closure_body: String,
  63     reverse: bool,
  64     unstable: bool,
  65 }
  66
  67 /// Detect if the two expressions are mirrored (identical, except one
  68 /// contains a and the other replaces it with b)
  69 fn mirrored_exprs(
  70     cx: &LateContext<'_>,
  71     a_expr: &Expr<'_>,
  72     a_ident: &Ident,
  73     b_expr: &Expr<'_>,
  74     b_ident: &Ident,
  75 ) -> bool {
  76     match (&a_expr.kind, &b_expr.kind) {
  77         // Two boxes with mirrored contents
  78         (ExprKind::Box(left_expr), ExprKind::Box(right_expr)) => {
  79             mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
  80         },
  81         // Two arrays with mirrored contents
  82         (ExprKind::Array(left_exprs), ExprKind::Array(right_exprs)) => {
  83             iter::zip(*left_exprs, *right_exprs).all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
  84         },
  85         // The two exprs are function calls.
  86         // Check to see that the function itself and its arguments are mirrored
  87         (ExprKind::Call(left_expr, left_args), ExprKind::Call(right_expr, right_args)) => {
  88             mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
  89                 && iter::zip(*left_args, *right_args)
  90                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
  91         },
  92         // The two exprs are method calls.
  93         // Check to see that the function is the same and the arguments are mirrored
  94         // This is enough because the receiver of the method is listed in the arguments
  95         (
  96             ExprKind::MethodCall(left_segment, _, left_args, _),
  97             ExprKind::MethodCall(right_segment, _, right_args, _),
  98         ) => {
  99             left_segment.ident == right_segment.ident
 100                 && iter::zip(*left_args, *right_args)
 101                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
 102         },
 103         // Two tuples with mirrored contents
 104         (ExprKind::Tup(left_exprs), ExprKind::Tup(right_exprs)) => {
 105             iter::zip(*left_exprs, *right_exprs).all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
 106         },
 107         // Two binary ops, which are the same operation and which have mirrored arguments
 108         (ExprKind::Binary(left_op, left_left, left_right), ExprKind::Binary(right_op, right_left, right_right)) => {
 109             left_op.node == right_op.node
 110                 && mirrored_exprs(cx, left_left, a_ident, right_left, b_ident)
 111                 && mirrored_exprs(cx, left_right, a_ident, right_right, b_ident)
 112         },
 113         // Two unary ops, which are the same operation and which have the same argument
 114         (ExprKind::Unary(left_op, left_expr), ExprKind::Unary(right_op, right_expr)) => {
 115             left_op == right_op && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
 116         },
 117         // The two exprs are literals of some kind
 118         (ExprKind::Lit(left_lit), ExprKind::Lit(right_lit)) => left_lit.node == right_lit.node,
 119         (ExprKind::Cast(left, _), ExprKind::Cast(right, _)) => mirrored_exprs(cx, left, a_ident, right, b_ident),
 120         (ExprKind::DropTemps(left_block), ExprKind::DropTemps(right_block)) => {
 121             mirrored_exprs(cx, left_block, a_ident, right_block, b_ident)
 122         },
 123         (ExprKind::Field(left_expr, left_ident), ExprKind::Field(right_expr, right_ident)) => {
 124             left_ident.name == right_ident.name && mirrored_exprs(cx, left_expr, a_ident, right_expr, right_ident)
 125         },
 126         // Two paths: either one is a and the other is b, or they're identical to each other
 127         (
 128             ExprKind::Path(QPath::Resolved(
 129                 _,
 130                 Path {
 131                     segments: left_segments,
 132                     ..
 133                 },
 134             )),
 135             ExprKind::Path(QPath::Resolved(
 136                 _,
 137                 Path {
 138                     segments: right_segments,
 139                     ..
 140                 },
 141             )),
 142         ) => {
 143             (iter::zip(*left_segments, *right_segments).all(|(left, right)| left.ident == right.ident)
 144                 && left_segments
 145                     .iter()
 146                     .all(|seg| &seg.ident != a_ident && &seg.ident != b_ident))
 147                 || (left_segments.len() == 1
 148                     && &left_segments[0].ident == a_ident
 149                     && right_segments.len() == 1
 150                     && &right_segments[0].ident == b_ident)
 151         },
 152         // Matching expressions, but one or both is borrowed
 153         (
 154             ExprKind::AddrOf(left_kind, Mutability::Not, left_expr),
 155             ExprKind::AddrOf(right_kind, Mutability::Not, right_expr),
 156         ) => left_kind == right_kind && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident),
 157         (_, ExprKind::AddrOf(_, Mutability::Not, right_expr)) => {
 158             mirrored_exprs(cx, a_expr, a_ident, right_expr, b_ident)
 159         },
 160         (ExprKind::AddrOf(_, Mutability::Not, left_expr), _) => mirrored_exprs(cx, left_expr, a_ident, b_expr, b_ident),
 161         _ => false,
 162     }
 163 }
 164
 165 fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
 166     if_chain! {
 167         if let ExprKind::MethodCall(name_ident, _, args, _) = &expr.kind;
 168         if let name = name_ident.ident.name.to_ident_string();
 169         if name == "sort_by" || name == "sort_unstable_by";
 170         if let [vec, Expr { kind: ExprKind::Closure(_, _, closure_body_id, _, _), .. }] = args;
 171         if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(vec), sym::Vec);
 172         if let closure_body = cx.tcx.hir().body(*closure_body_id);
 173         if let &[
 174             Param { pat: Pat { kind: PatKind::Binding(_, _, left_ident, _), .. }, ..},
 175             Param { pat: Pat { kind: PatKind::Binding(_, _, right_ident, _), .. }, .. }
 176         ] = &closure_body.params;
 177         if let ExprKind::MethodCall(method_path, _, [ref left_expr, ref right_expr], _) = &closure_body.value.kind;
 178         if method_path.ident.name == sym::cmp;
 179         then {
 180             let (closure_body, closure_arg, reverse) = if mirrored_exprs(
 181                 cx,
 182                 left_expr,
 183                 left_ident,
 184                 right_expr,
 185                 right_ident
 186             ) {
 187                 (Sugg::hir(cx, left_expr, "..").to_string(), left_ident.name.to_string(), false)
 188             } else if mirrored_exprs(cx, left_expr, right_ident, right_expr, left_ident) {
 189                 (Sugg::hir(cx, left_expr, "..").to_string(), right_ident.name.to_string(), true)
 190             } else {
 191                 return None;
 192             };
 193             let vec_name = Sugg::hir(cx, &args[0], "..").to_string();
 194             let unstable = name == "sort_unstable_by";
 195
 196             if_chain! {
 197             if let ExprKind::Path(QPath::Resolved(_, Path {
 198                 segments: [PathSegment { ident: left_name, .. }], ..
 199             })) = &left_expr.kind;
 200             if left_name == left_ident;
 201             if cx.tcx.get_diagnostic_item(sym::Ord).map_or(false, |id| {
 202                 implements_trait(cx, cx.typeck_results().expr_ty(left_expr), id, &[])
 203             });
 204                 then {
 205                     return Some(LintTrigger::Sort(SortDetection { vec_name, unstable }));
 206                 }
 207             }
 208
 209             if !expr_borrows(cx, left_expr) {
 210                 return Some(LintTrigger::SortByKey(SortByKeyDetection {
 211                     vec_name,
 212                     closure_arg,
 213                     closure_body,
 214                     reverse,
 215                     unstable,
 216                 }));
 217             }
 218         }
 219     }
 220
 221     None
 222 }
 223
 224 fn expr_borrows(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 225     let ty = cx.typeck_results().expr_ty(expr);
 226     matches!(ty.kind(), ty::Ref(..))
 227         || ty
 228             .walk(cx.tcx)
 229             .any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(_)))
 230 }
 231
 232 impl LateLintPass<'_> for UnnecessarySortBy {
 233     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
 234         match detect_lint(cx, expr) {
 235             Some(LintTrigger::SortByKey(trigger)) => span_lint_and_sugg(
 236                 cx,
 237                 UNNECESSARY_SORT_BY,
 238                 expr.span,
 239                 "use Vec::sort_by_key here instead",
 240                 "try",
 241                 format!(
 242                     "{}.sort{}_by_key(|{}| {})",
 243                     trigger.vec_name,
 244                     if trigger.unstable { "_unstable" } else { "" },
 245                     trigger.closure_arg,
 246                     if trigger.reverse {
 247                         format!("Reverse({})", trigger.closure_body)
 248                     } else {
 249                         trigger.closure_body.to_string()
 250                     },
 251                 ),
 252                 if trigger.reverse {
 253                     Applicability::MaybeIncorrect
 254                 } else {
 255                     Applicability::MachineApplicable
 256                 },
 257             ),
 258             Some(LintTrigger::Sort(trigger)) => span_lint_and_sugg(
 259                 cx,
 260                 UNNECESSARY_SORT_BY,
 261                 expr.span,
 262                 "use Vec::sort here instead",
 263                 "try",
 264                 format!(
 265                     "{}.sort{}()",
 266                     trigger.vec_name,
 267                     if trigger.unstable { "_unstable" } else { "" },
 268                 ),
 269                 Applicability::MachineApplicable,
 270             ),
 271             None => {},
 272         }
 273     }
 274 }