src/tools/clippy/clippy_lints/src/unnecessary_sort_by.rs

   1 use crate::utils;
   2 use crate::utils::paths;
   3 use crate::utils::sugg::Sugg;
   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_session::{declare_lint_pass, declare_tool_lint};
   9 use rustc_span::symbol::Ident;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:**
  13     /// Detects when people use `Vec::sort_by` and pass in a function
  14     /// which compares the two arguments, either directly or indirectly.
  15     ///
  16     /// **Why is this bad?**
  17     /// It is more clear to use `Vec::sort_by_key` (or `Vec::sort` if
  18     /// possible) than to use `Vec::sort_by` and and a more complicated
  19     /// closure.
  20     ///
  21     /// **Known problems:**
  22     /// If the suggested `Vec::sort_by_key` uses Reverse and it isn't
  23     /// imported by a use statement in the current frame, then a `use`
  24     /// statement that imports it will need to be added (which this lint
  25     /// can't do).
  26     ///
  27     /// **Example:**
  28     ///
  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)) => left_exprs
  83             .iter()
  84             .zip(right_exprs.iter())
  85             .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident)),
  86         // The two exprs are function calls.
  87         // Check to see that the function itself and its arguments are mirrored
  88         (ExprKind::Call(left_expr, left_args), ExprKind::Call(right_expr, right_args)) => {
  89             mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
  90                 && left_args
  91                     .iter()
  92                     .zip(right_args.iter())
  93                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
  94         },
  95         // The two exprs are method calls.
  96         // Check to see that the function is the same and the arguments are mirrored
  97         // This is enough because the receiver of the method is listed in the arguments
  98         (
  99             ExprKind::MethodCall(left_segment, _, left_args, _),
 100             ExprKind::MethodCall(right_segment, _, right_args, _),
 101         ) => {
 102             left_segment.ident == right_segment.ident
 103                 && left_args
 104                     .iter()
 105                     .zip(right_args.iter())
 106                     .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident))
 107         },
 108         // Two tuples with mirrored contents
 109         (ExprKind::Tup(left_exprs), ExprKind::Tup(right_exprs)) => left_exprs
 110             .iter()
 111             .zip(right_exprs.iter())
 112             .all(|(left, right)| mirrored_exprs(cx, left, a_ident, right, b_ident)),
 113         // Two binary ops, which are the same operation and which have mirrored arguments
 114         (ExprKind::Binary(left_op, left_left, left_right), ExprKind::Binary(right_op, right_left, right_right)) => {
 115             left_op.node == right_op.node
 116                 && mirrored_exprs(cx, left_left, a_ident, right_left, b_ident)
 117                 && mirrored_exprs(cx, left_right, a_ident, right_right, b_ident)
 118         },
 119         // Two unary ops, which are the same operation and which have the same argument
 120         (ExprKind::Unary(left_op, left_expr), ExprKind::Unary(right_op, right_expr)) => {
 121             left_op == right_op && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident)
 122         },
 123         // The two exprs are literals of some kind
 124         (ExprKind::Lit(left_lit), ExprKind::Lit(right_lit)) => left_lit.node == right_lit.node,
 125         (ExprKind::Cast(left, _), ExprKind::Cast(right, _)) => mirrored_exprs(cx, left, a_ident, right, b_ident),
 126         (ExprKind::DropTemps(left_block), ExprKind::DropTemps(right_block)) => {
 127             mirrored_exprs(cx, left_block, a_ident, right_block, b_ident)
 128         },
 129         (ExprKind::Field(left_expr, left_ident), ExprKind::Field(right_expr, right_ident)) => {
 130             left_ident.name == right_ident.name && mirrored_exprs(cx, left_expr, a_ident, right_expr, right_ident)
 131         },
 132         // Two paths: either one is a and the other is b, or they're identical to each other
 133         (
 134             ExprKind::Path(QPath::Resolved(
 135                 _,
 136                 Path {
 137                     segments: left_segments,
 138                     ..
 139                 },
 140             )),
 141             ExprKind::Path(QPath::Resolved(
 142                 _,
 143                 Path {
 144                     segments: right_segments,
 145                     ..
 146                 },
 147             )),
 148         ) => {
 149             (left_segments
 150                 .iter()
 151                 .zip(right_segments.iter())
 152                 .all(|(left, right)| left.ident == right.ident)
 153                 && left_segments
 154                     .iter()
 155                     .all(|seg| &seg.ident != a_ident && &seg.ident != b_ident))
 156                 || (left_segments.len() == 1
 157                     && &left_segments[0].ident == a_ident
 158                     && right_segments.len() == 1
 159                     && &right_segments[0].ident == b_ident)
 160         },
 161         // Matching expressions, but one or both is borrowed
 162         (
 163             ExprKind::AddrOf(left_kind, Mutability::Not, left_expr),
 164             ExprKind::AddrOf(right_kind, Mutability::Not, right_expr),
 165         ) => left_kind == right_kind && mirrored_exprs(cx, left_expr, a_ident, right_expr, b_ident),
 166         (_, ExprKind::AddrOf(_, Mutability::Not, right_expr)) => {
 167             mirrored_exprs(cx, a_expr, a_ident, right_expr, b_ident)
 168         },
 169         (ExprKind::AddrOf(_, Mutability::Not, left_expr), _) => mirrored_exprs(cx, left_expr, a_ident, b_expr, b_ident),
 170         _ => false,
 171     }
 172 }
 173
 174 fn detect_lint(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintTrigger> {
 175     if_chain! {
 176         if let ExprKind::MethodCall(name_ident, _, args, _) = &expr.kind;
 177         if let name = name_ident.ident.name.to_ident_string();
 178         if name == "sort_by" || name == "sort_unstable_by";
 179         if let [vec, Expr { kind: ExprKind::Closure(_, _, closure_body_id, _, _), .. }] = args;
 180         if utils::match_type(cx, &cx.tables().expr_ty(vec), &paths::VEC);
 181         if let closure_body = cx.tcx.hir().body(*closure_body_id);
 182         if let &[
 183             Param { pat: Pat { kind: PatKind::Binding(_, _, left_ident, _), .. }, ..},
 184             Param { pat: Pat { kind: PatKind::Binding(_, _, right_ident, _), .. }, .. }
 185         ] = &closure_body.params;
 186         if let ExprKind::MethodCall(method_path, _, [ref left_expr, ref right_expr], _) = &closure_body.value.kind;
 187         if method_path.ident.name.to_ident_string() == "cmp";
 188         then {
 189             let (closure_body, closure_arg, reverse) = if mirrored_exprs(
 190                 &cx,
 191                 &left_expr,
 192                 &left_ident,
 193                 &right_expr,
 194                 &right_ident
 195             ) {
 196                 (Sugg::hir(cx, &left_expr, "..").to_string(), left_ident.name.to_string(), false)
 197             } else if mirrored_exprs(&cx, &left_expr, &right_ident, &right_expr, &left_ident) {
 198                 (Sugg::hir(cx, &left_expr, "..").to_string(), right_ident.name.to_string(), true)
 199             } else {
 200                 return None;
 201             };
 202             let vec_name = Sugg::hir(cx, &args[0], "..").to_string();
 203             let unstable = name == "sort_unstable_by";
 204             if_chain! {
 205                 if let ExprKind::Path(QPath::Resolved(_, Path {
 206                     segments: [PathSegment { ident: left_name, .. }], ..
 207                 })) = &left_expr.kind;
 208                 if left_name == left_ident;
 209                 then {
 210                     Some(LintTrigger::Sort(SortDetection { vec_name, unstable }))
 211                 }
 212                 else {
 213                     Some(LintTrigger::SortByKey(SortByKeyDetection {
 214                         vec_name,
 215                         unstable,
 216                         closure_arg,
 217                         closure_body,
 218                         reverse
 219                     }))
 220                 }
 221             }
 222         } else {
 223             None
 224         }
 225     }
 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)) => utils::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)) => utils::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 }