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::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     ///
  30     /// ```rust
  31     /// # struct A;
  32     /// # impl A { fn foo(&self) {} }
  33     /// # let mut vec: Vec<A> = Vec::new();
  34     /// vec.sort_by(|a, b| a.foo().cmp(&b.foo()));
  35     /// ```
  36     /// Use instead:
  37     /// ```rust
  38     /// # struct A;
  39     /// # impl A { fn foo(&self) {} }
  40     /// # let mut vec: Vec<A> = Vec::new();
  41     /// vec.sort_by_key(|a| a.foo());
  42     /// ```
  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(
  71     cx: &LateContext<'_>,
  72     a_expr: &Expr<'_>,
  73     a_ident: &Ident,
  74     b_expr: &Expr<'_>,
  75     b_ident: &Ident,
  76 ) -> bool {
  77     match (&a_expr.kind, &b_expr.kind) {
  78         // Two boxes with mirrored contents
  79         (ExprKind::Box(left_expr), ExprKind::Box(right_expr)) => {
  80             mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
  81         },
  82         // Two arrays with mirrored contents
  83         (ExprKind::Array(left_exprs), ExprKind::Array(right_exprs)) => {
  84             iter::zip(*left_exprs, *right_exprs)
  85                 .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
  86         }
  87         // The two exprs are function calls.
  88         // Check to see that the function itself and its arguments are mirrored
  89         (ExprKind::Call(left_expr, left_args), ExprKind::Call(right_expr, right_args)) => {
  90             mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
  91                 && iter::zip(*left_args, *right_args)
  92                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
  93         },
  94         // The two exprs are method calls.
  95         // Check to see that the function is the same and the arguments are mirrored
  96         // This is enough because the receiver of the method is listed in the arguments
  97         (
  98             ExprKind::MethodCall(left_segment, _, left_args, _),
  99             ExprKind::MethodCall(right_segment, _, right_args, _),
 100         ) => {
 101             left_segment.ident == right_segment.ident
 102                 && iter::zip(*left_args, *right_args)
 103                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
 104         }
 105         // Two tuples with mirrored contents
 106         (ExprKind::Tup(left_exprs), ExprKind::Tup(right_exprs)) => {
 107             iter::zip(*left_exprs, *right_exprs)
 108                 .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
 109         }
 110         // Two binary ops, which are the same operation and which have mirrored arguments
 111         (ExprKind::Binary(left_op, left_left, left_right), ExprKind::Binary(right_op, right_left, right_right)) => {
 112             left_op.node == right_op.node
 113                 && mirrored_exprs(cx, left_left, a_ident, right_left, b_ident)
 114                 && mirrored_exprs(cx, left_right, a_ident, right_right, b_ident)
 115         },
 116         // Two unary ops, which are the same operation and which have the same argument
 117         (ExprKind::Unary(left_op, left_expr), ExprKind::Unary(right_op, right_expr)) => {
 118             left_op == right_op && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
 119         },
 120         // The two exprs are literals of some kind
 121         (ExprKind::Lit(left_lit), ExprKind::Lit(right_lit)) => left_lit.node == right_lit.node,
 122         (ExprKind::Cast(left, _), ExprKind::Cast(right, _)) => mirrored_exprs(cx, left, a_ident, right, b_ident),
 123         (ExprKind::DropTemps(left_block), ExprKind::DropTemps(right_block)) => {
 124             mirrored_exprs(cx, left_block, a_ident, right_block, b_ident)
 125         },
 126         (ExprKind::Field(left_expr, left_ident), ExprKind::Field(right_expr, right_ident)) => {
 127             left_ident.name == right_ident.name && mirrored_exprs(cx, left_expr, a_ident, right_expr, right_ident)
 128         },
 129         // Two paths: either one is a and the other is b, or they're identical to each other
 130         (
 131             ExprKind::Path(QPath::Resolved(
 132                 _,
 133                 Path {
 134                     segments: left_segments,
 135                     ..
 136                 },
 137             )),
 138             ExprKind::Path(QPath::Resolved(
 139                 _,
 140                 Path {
 141                     segments: right_segments,
 142                     ..
 143                 },
 144             )),
 145         ) => {
 146             (iter::zip(*left_segments, *right_segments)
 147                 .all(|(left, right)| left.ident == right.ident)
 148                 && left_segments
 149                     .iter()
 150                     .all(|seg| &seg.ident != a_ident && &seg.ident != b_ident))
 151                 || (left_segments.len() == 1
 152                     && &left_segments[0].ident == a_ident
 153                     && right_segments.len() == 1
 154                     && &right_segments[0].ident == b_ident)
 155         },
 156         // Matching expressions, but one or both is borrowed
 157         (
 158             ExprKind::AddrOf(left_kind, Mutability::Not, left_expr),
 159             ExprKind::AddrOf(right_kind, Mutability::Not, right_expr),
 160         ) => left_kind == right_kind && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident),
 161         (_, ExprKind::AddrOf(_, Mutability::Not, right_expr)) => {
 162             mirrored_exprs(cx, a_expr, a_ident, right_expr, b_ident)
 163         },
 164         (ExprKind::AddrOf(_, Mutability::Not, left_expr), _) => mirrored_exprs(cx, left_expr, a_ident, b_expr, b_ident),
 165         _ => false,
 166     }
 167 }
 168
 169 fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
 170     if_chain! {
 171         if let ExprKind::MethodCall(name_ident, _, args, _) = &expr.kind;
 172         if let name = name_ident.ident.name.to_ident_string();
 173         if name == "sort_by" || name == "sort_unstable_by";
 174         if let [vec, Expr { kind: ExprKind::Closure(_, _, closure_body_id, _, _), .. }] = args;
 175         if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(vec), sym::vec_type);
 176         if let closure_body = cx.tcx.hir().body(*closure_body_id);
 177         if let &[
 178             Param { pat: Pat { kind: PatKind::Binding(_, _, left_ident, _), .. }, ..},
 179             Param { pat: Pat { kind: PatKind::Binding(_, _, right_ident, _), .. }, .. }
 180         ] = &closure_body.params;
 181         if let ExprKind::MethodCall(method_path, _, [ref left_expr, ref right_expr], _) = &closure_body.value.kind;
 182         if method_path.ident.name == sym::cmp;
 183         then {
 184             let (closure_body, closure_arg, reverse) = if mirrored_exprs(
 185                 &cx,
 186                 &left_expr,
 187                 &left_ident,
 188                 &right_expr,
 189                 &right_ident
 190             ) {
 191                 (Sugg::hir(cx, &left_expr, "..").to_string(), left_ident.name.to_string(), false)
 192             } else if mirrored_exprs(&cx, &left_expr, &right_ident, &right_expr, &left_ident) {
 193                 (Sugg::hir(cx, &left_expr, "..").to_string(), right_ident.name.to_string(), true)
 194             } else {
 195                 return None;
 196             };
 197             let vec_name = Sugg::hir(cx, &args[0], "..").to_string();
 198             let unstable = name == "sort_unstable_by";
 199
 200             if let ExprKind::Path(QPath::Resolved(_, Path {
 201                 segments: [PathSegment { ident: left_name, .. }], ..
 202             })) = &left_expr.kind {
 203                 if left_name == left_ident {
 204                     return Some(LintTrigger::Sort(SortDetection { vec_name, unstable }));
 205                 }
 206             }
 207
 208             if !expr_borrows(cx, left_expr) {
 209                 return Some(LintTrigger::SortByKey(SortByKeyDetection {
 210                     vec_name,
 211                     closure_arg,
 212                     closure_body,
 213                     reverse,
 214                     unstable,
 215                 }));
 216             }
 217         }
 218     }
 219
 220     None
 221 }
 222
 223 fn expr_borrows(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 224     let ty = cx.typeck_results().expr_ty(expr);
 225     matches!(ty.kind(), ty::Ref(..)) || ty.walk().any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(_)))
 226 }
 227
 228 impl LateLintPass<'_> for UnnecessarySortBy {
 229     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
 230         match detect_lint(cx, expr) {
 231             Some(LintTrigger::SortByKey(trigger)) => span_lint_and_sugg(
 232                 cx,
 233                 UNNECESSARY_SORT_BY,
 234                 expr.span,
 235                 "use Vec::sort_by_key here instead",
 236                 "try",
 237                 format!(
 238                     "{}.sort{}_by_key(|{}| {})",
 239                     trigger.vec_name,
 240                     if trigger.unstable { "_unstable" } else { "" },
 241                     trigger.closure_arg,
 242                     if trigger.reverse {
 243                         format!("Reverse({})", trigger.closure_body)
 244                     } else {
 245                         trigger.closure_body.to_string()
 246                     },
 247                 ),
 248                 if trigger.reverse {
 249                     Applicability::MaybeIncorrect
 250                 } else {
 251                     Applicability::MachineApplicable
 252                 },
 253             ),
 254             Some(LintTrigger::Sort(trigger)) => span_lint_and_sugg(
 255                 cx,
 256                 UNNECESSARY_SORT_BY,
 257                 expr.span,
 258                 "use Vec::sort here instead",
 259                 "try",
 260                 format!(
 261                     "{}.sort{}()",
 262                     trigger.vec_name,
 263                     if trigger.unstable { "_unstable" } else { "" },
 264                 ),
 265                 Applicability::MachineApplicable,
 266             ),
 267             None => {},
 268         }
 269     }
 270 }