src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::{path_to_local, search_same, SpanlessEq, SpanlessHash};
   4 use core::cmp::Ordering;
   5 use core::iter;
   6 use core::slice;
   7 use rustc_arena::DroplessArena;
   8 use rustc_ast::ast::LitKind;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::{Arm, Expr, ExprKind, HirId, HirIdMap, HirIdMapEntry, HirIdSet, Pat, PatKind, RangeEnd};
  12 use rustc_lint::LateContext;
  13 use rustc_middle::ty;
  14 use rustc_span::Symbol;
  15
  16 use super::MATCH_SAME_ARMS;
  17
  18 #[expect(clippy::too_many_lines)]
  19 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>]) {
  20     let hash = |&(_, arm): &(usize, &Arm<'_>)| -> u64 {
  21         let mut h = SpanlessHash::new(cx);
  22         h.hash_expr(arm.body);
  23         h.finish()
  24     };
  25
  26     let arena = DroplessArena::default();
  27     let normalized_pats: Vec<_> = arms
  28         .iter()
  29         .map(|a| NormalizedPat::from_pat(cx, &arena, a.pat))
  30         .collect();
  31
  32     // The furthest forwards a pattern can move without semantic changes
  33     let forwards_blocking_idxs: Vec<_> = normalized_pats
  34         .iter()
  35         .enumerate()
  36         .map(|(i, pat)| {
  37             normalized_pats[i + 1..]
  38                 .iter()
  39                 .enumerate()
  40                 .find_map(|(j, other)| pat.has_overlapping_values(other).then_some(i + 1 + j))
  41                 .unwrap_or(normalized_pats.len())
  42         })
  43         .collect();
  44
  45     // The furthest backwards a pattern can move without semantic changes
  46     let backwards_blocking_idxs: Vec<_> = normalized_pats
  47         .iter()
  48         .enumerate()
  49         .map(|(i, pat)| {
  50             normalized_pats[..i]
  51                 .iter()
  52                 .enumerate()
  53                 .rev()
  54                 .zip(forwards_blocking_idxs[..i].iter().copied().rev())
  55                 .skip_while(|&(_, forward_block)| forward_block > i)
  56                 .find_map(|((j, other), forward_block)| {
  57                     (forward_block == i || pat.has_overlapping_values(other)).then_some(j)
  58                 })
  59                 .unwrap_or(0)
  60         })
  61         .collect();
  62
  63     let eq = |&(lindex, lhs): &(usize, &Arm<'_>), &(rindex, rhs): &(usize, &Arm<'_>)| -> bool {
  64         let min_index = usize::min(lindex, rindex);
  65         let max_index = usize::max(lindex, rindex);
  66
  67         let mut local_map: HirIdMap<HirId> = HirIdMap::default();
  68         let eq_fallback = |a: &Expr<'_>, b: &Expr<'_>| {
  69             if_chain! {
  70                 if let Some(a_id) = path_to_local(a);
  71                 if let Some(b_id) = path_to_local(b);
  72                 let entry = match local_map.entry(a_id) {
  73                     HirIdMapEntry::Vacant(entry) => entry,
  74                     // check if using the same bindings as before
  75                     HirIdMapEntry::Occupied(entry) => return *entry.get() == b_id,
  76                 };
  77                 // the names technically don't have to match; this makes the lint more conservative
  78                 if cx.tcx.hir().name(a_id) == cx.tcx.hir().name(b_id);
  79                 if cx.typeck_results().expr_ty(a) == cx.typeck_results().expr_ty(b);
  80                 if pat_contains_local(lhs.pat, a_id);
  81                 if pat_contains_local(rhs.pat, b_id);
  82                 then {
  83                     entry.insert(b_id);
  84                     true
  85                 } else {
  86                     false
  87                 }
  88             }
  89         };
  90         // Arms with a guard are ignored, those can’t always be merged together
  91         // If both arms overlap with an arm in between then these can't be merged either.
  92         !(backwards_blocking_idxs[max_index] > min_index && forwards_blocking_idxs[min_index] < max_index)
  93                 && lhs.guard.is_none()
  94                 && rhs.guard.is_none()
  95                 && SpanlessEq::new(cx)
  96                     .expr_fallback(eq_fallback)
  97                     .eq_expr(lhs.body, rhs.body)
  98                 // these checks could be removed to allow unused bindings
  99                 && bindings_eq(lhs.pat, local_map.keys().copied().collect())
 100                 && bindings_eq(rhs.pat, local_map.values().copied().collect())
 101     };
 102
 103     let indexed_arms: Vec<(usize, &Arm<'_>)> = arms.iter().enumerate().collect();
 104     for (&(i, arm1), &(j, arm2)) in search_same(&indexed_arms, hash, eq) {
 105         if matches!(arm2.pat.kind, PatKind::Wild) {
 106             span_lint_and_then(
 107                 cx,
 108                 MATCH_SAME_ARMS,
 109                 arm1.span,
 110                 "this match arm has an identical body to the `_` wildcard arm",
 111                 |diag| {
 112                     diag.span_suggestion(arm1.span, "try removing the arm", "", Applicability::MaybeIncorrect)
 113                         .help("or try changing either arm body")
 114                         .span_note(arm2.span, "`_` wildcard arm here");
 115                 },
 116             );
 117         } else {
 118             let back_block = backwards_blocking_idxs[j];
 119             let (keep_arm, move_arm) = if back_block < i || (back_block == 0 && forwards_blocking_idxs[i] <= j) {
 120                 (arm1, arm2)
 121             } else {
 122                 (arm2, arm1)
 123             };
 124
 125             span_lint_and_then(
 126                 cx,
 127                 MATCH_SAME_ARMS,
 128                 keep_arm.span,
 129                 "this match arm has an identical body to another arm",
 130                 |diag| {
 131                     let move_pat_snip = snippet(cx, move_arm.pat.span, "<pat2>");
 132                     let keep_pat_snip = snippet(cx, keep_arm.pat.span, "<pat1>");
 133
 134                     diag.span_suggestion(
 135                         keep_arm.pat.span,
 136                         "try merging the arm patterns",
 137                         format!("{keep_pat_snip} | {move_pat_snip}"),
 138                         Applicability::MaybeIncorrect,
 139                     )
 140                     .help("or try changing either arm body")
 141                     .span_note(move_arm.span, "other arm here");
 142                 },
 143             );
 144         }
 145     }
 146 }
 147
 148 #[derive(Clone, Copy)]
 149 enum NormalizedPat<'a> {
 150     Wild,
 151     Struct(Option<DefId>, &'a [(Symbol, Self)]),
 152     Tuple(Option<DefId>, &'a [Self]),
 153     Or(&'a [Self]),
 154     Path(Option<DefId>),
 155     LitStr(Symbol),
 156     LitBytes(&'a [u8]),
 157     LitInt(u128),
 158     LitBool(bool),
 159     Range(PatRange),
 160     /// A slice pattern. If the second value is `None`, then this matches an exact size. Otherwise
 161     /// the first value contains everything before the `..` wildcard pattern, and the second value
 162     /// contains everything afterwards. Note that either side, or both sides, may contain zero
 163     /// patterns.
 164     Slice(&'a [Self], Option<&'a [Self]>),
 165 }
 166
 167 #[derive(Clone, Copy)]
 168 struct PatRange {
 169     start: u128,
 170     end: u128,
 171     bounds: RangeEnd,
 172 }
 173 impl PatRange {
 174     fn contains(&self, x: u128) -> bool {
 175         x >= self.start
 176             && match self.bounds {
 177                 RangeEnd::Included => x <= self.end,
 178                 RangeEnd::Excluded => x < self.end,
 179             }
 180     }
 181
 182     fn overlaps(&self, other: &Self) -> bool {
 183         // Note: Empty ranges are impossible, so this is correct even though it would return true if an
 184         // empty exclusive range were to reside within an inclusive range.
 185         (match self.bounds {
 186             RangeEnd::Included => self.end >= other.start,
 187             RangeEnd::Excluded => self.end > other.start,
 188         } && match other.bounds {
 189             RangeEnd::Included => self.start <= other.end,
 190             RangeEnd::Excluded => self.start < other.end,
 191         })
 192     }
 193 }
 194
 195 /// Iterates over the pairs of fields with matching names.
 196 fn iter_matching_struct_fields<'a>(
 197     left: &'a [(Symbol, NormalizedPat<'a>)],
 198     right: &'a [(Symbol, NormalizedPat<'a>)],
 199 ) -> impl Iterator<Item = (&'a NormalizedPat<'a>, &'a NormalizedPat<'a>)> + 'a {
 200     struct Iter<'a>(
 201         slice::Iter<'a, (Symbol, NormalizedPat<'a>)>,
 202         slice::Iter<'a, (Symbol, NormalizedPat<'a>)>,
 203     );
 204     impl<'a> Iterator for Iter<'a> {
 205         type Item = (&'a NormalizedPat<'a>, &'a NormalizedPat<'a>);
 206         fn next(&mut self) -> Option<Self::Item> {
 207             // Note: all the fields in each slice are sorted by symbol value.
 208             let mut left = self.0.next()?;
 209             let mut right = self.1.next()?;
 210             loop {
 211                 match left.0.cmp(&right.0) {
 212                     Ordering::Equal => return Some((&left.1, &right.1)),
 213                     Ordering::Less => left = self.0.next()?,
 214                     Ordering::Greater => right = self.1.next()?,
 215                 }
 216             }
 217         }
 218     }
 219     Iter(left.iter(), right.iter())
 220 }
 221
 222 #[expect(clippy::similar_names)]
 223 impl<'a> NormalizedPat<'a> {
 224     fn from_pat(cx: &LateContext<'_>, arena: &'a DroplessArena, pat: &'a Pat<'_>) -> Self {
 225         match pat.kind {
 226             PatKind::Wild | PatKind::Binding(.., None) => Self::Wild,
 227             PatKind::Binding(.., Some(pat)) | PatKind::Box(pat) | PatKind::Ref(pat, _) => {
 228                 Self::from_pat(cx, arena, pat)
 229             },
 230             PatKind::Struct(ref path, fields, _) => {
 231                 let fields =
 232                     arena.alloc_from_iter(fields.iter().map(|f| (f.ident.name, Self::from_pat(cx, arena, f.pat))));
 233                 fields.sort_by_key(|&(name, _)| name);
 234                 Self::Struct(cx.qpath_res(path, pat.hir_id).opt_def_id(), fields)
 235             },
 236             PatKind::TupleStruct(ref path, pats, wild_idx) => {
 237                 let Some(adt) = cx.typeck_results().pat_ty(pat).ty_adt_def() else {
 238                     return Self::Wild
 239                 };
 240                 let (var_id, variant) = if adt.is_enum() {
 241                     match cx.qpath_res(path, pat.hir_id).opt_def_id() {
 242                         Some(x) => (Some(x), adt.variant_with_ctor_id(x)),
 243                         None => return Self::Wild,
 244                     }
 245                 } else {
 246                     (None, adt.non_enum_variant())
 247                 };
 248                 let (front, back) = match wild_idx.as_opt_usize() {
 249                     Some(i) => pats.split_at(i),
 250                     None => (pats, [].as_slice()),
 251                 };
 252                 let pats = arena.alloc_from_iter(
 253                     front
 254                         .iter()
 255                         .map(|pat| Self::from_pat(cx, arena, pat))
 256                         .chain(iter::repeat_with(|| Self::Wild).take(variant.fields.len() - pats.len()))
 257                         .chain(back.iter().map(|pat| Self::from_pat(cx, arena, pat))),
 258                 );
 259                 Self::Tuple(var_id, pats)
 260             },
 261             PatKind::Or(pats) => Self::Or(arena.alloc_from_iter(pats.iter().map(|pat| Self::from_pat(cx, arena, pat)))),
 262             PatKind::Path(ref path) => Self::Path(cx.qpath_res(path, pat.hir_id).opt_def_id()),
 263             PatKind::Tuple(pats, wild_idx) => {
 264                 let field_count = match cx.typeck_results().pat_ty(pat).kind() {
 265                     ty::Tuple(subs) => subs.len(),
 266                     _ => return Self::Wild,
 267                 };
 268                 let (front, back) = match wild_idx.as_opt_usize() {
 269                     Some(i) => pats.split_at(i),
 270                     None => (pats, [].as_slice()),
 271                 };
 272                 let pats = arena.alloc_from_iter(
 273                     front
 274                         .iter()
 275                         .map(|pat| Self::from_pat(cx, arena, pat))
 276                         .chain(iter::repeat_with(|| Self::Wild).take(field_count - pats.len()))
 277                         .chain(back.iter().map(|pat| Self::from_pat(cx, arena, pat))),
 278                 );
 279                 Self::Tuple(None, pats)
 280             },
 281             PatKind::Lit(e) => match &e.kind {
 282                 // TODO: Handle negative integers. They're currently treated as a wild match.
 283                 ExprKind::Lit(lit) => match lit.node {
 284                     LitKind::Str(sym, _) => Self::LitStr(sym),
 285                     LitKind::ByteStr(ref bytes, _) => Self::LitBytes(bytes),
 286                     LitKind::Byte(val) => Self::LitInt(val.into()),
 287                     LitKind::Char(val) => Self::LitInt(val.into()),
 288                     LitKind::Int(val, _) => Self::LitInt(val),
 289                     LitKind::Bool(val) => Self::LitBool(val),
 290                     LitKind::Float(..) | LitKind::Err => Self::Wild,
 291                 },
 292                 _ => Self::Wild,
 293             },
 294             PatKind::Range(start, end, bounds) => {
 295                 // TODO: Handle negative integers. They're currently treated as a wild match.
 296                 let start = match start {
 297                     None => 0,
 298                     Some(e) => match &e.kind {
 299                         ExprKind::Lit(lit) => match lit.node {
 300                             LitKind::Int(val, _) => val,
 301                             LitKind::Char(val) => val.into(),
 302                             LitKind::Byte(val) => val.into(),
 303                             _ => return Self::Wild,
 304                         },
 305                         _ => return Self::Wild,
 306                     },
 307                 };
 308                 let (end, bounds) = match end {
 309                     None => (u128::MAX, RangeEnd::Included),
 310                     Some(e) => match &e.kind {
 311                         ExprKind::Lit(lit) => match lit.node {
 312                             LitKind::Int(val, _) => (val, bounds),
 313                             LitKind::Char(val) => (val.into(), bounds),
 314                             LitKind::Byte(val) => (val.into(), bounds),
 315                             _ => return Self::Wild,
 316                         },
 317                         _ => return Self::Wild,
 318                     },
 319                 };
 320                 Self::Range(PatRange { start, end, bounds })
 321             },
 322             PatKind::Slice(front, wild_pat, back) => Self::Slice(
 323                 arena.alloc_from_iter(front.iter().map(|pat| Self::from_pat(cx, arena, pat))),
 324                 wild_pat.map(|_| &*arena.alloc_from_iter(back.iter().map(|pat| Self::from_pat(cx, arena, pat)))),
 325             ),
 326         }
 327     }
 328
 329     /// Checks if two patterns overlap in the values they can match assuming they are for the same
 330     /// type.
 331     fn has_overlapping_values(&self, other: &Self) -> bool {
 332         match (*self, *other) {
 333             (Self::Wild, _) | (_, Self::Wild) => true,
 334             (Self::Or(pats), ref other) | (ref other, Self::Or(pats)) => {
 335                 pats.iter().any(|pat| pat.has_overlapping_values(other))
 336             },
 337             (Self::Struct(lpath, lfields), Self::Struct(rpath, rfields)) => {
 338                 if lpath != rpath {
 339                     return false;
 340                 }
 341                 iter_matching_struct_fields(lfields, rfields).all(|(lpat, rpat)| lpat.has_overlapping_values(rpat))
 342             },
 343             (Self::Tuple(lpath, lpats), Self::Tuple(rpath, rpats)) => {
 344                 if lpath != rpath {
 345                     return false;
 346                 }
 347                 lpats
 348                     .iter()
 349                     .zip(rpats.iter())
 350                     .all(|(lpat, rpat)| lpat.has_overlapping_values(rpat))
 351             },
 352             (Self::Path(x), Self::Path(y)) => x == y,
 353             (Self::LitStr(x), Self::LitStr(y)) => x == y,
 354             (Self::LitBytes(x), Self::LitBytes(y)) => x == y,
 355             (Self::LitInt(x), Self::LitInt(y)) => x == y,
 356             (Self::LitBool(x), Self::LitBool(y)) => x == y,
 357             (Self::Range(ref x), Self::Range(ref y)) => x.overlaps(y),
 358             (Self::Range(ref range), Self::LitInt(x)) | (Self::LitInt(x), Self::Range(ref range)) => range.contains(x),
 359             (Self::Slice(lpats, None), Self::Slice(rpats, None)) => {
 360                 lpats.len() == rpats.len() && lpats.iter().zip(rpats.iter()).all(|(x, y)| x.has_overlapping_values(y))
 361             },
 362             (Self::Slice(pats, None), Self::Slice(front, Some(back)))
 363             | (Self::Slice(front, Some(back)), Self::Slice(pats, None)) => {
 364                 // Here `pats` is an exact size match. If the combined lengths of `front` and `back` are greater
 365                 // then the minimum length required will be greater than the length of `pats`.
 366                 if pats.len() < front.len() + back.len() {
 367                     return false;
 368                 }
 369                 pats[..front.len()]
 370                     .iter()
 371                     .zip(front.iter())
 372                     .chain(pats[pats.len() - back.len()..].iter().zip(back.iter()))
 373                     .all(|(x, y)| x.has_overlapping_values(y))
 374             },
 375             (Self::Slice(lfront, Some(lback)), Self::Slice(rfront, Some(rback))) => lfront
 376                 .iter()
 377                 .zip(rfront.iter())
 378                 .chain(lback.iter().rev().zip(rback.iter().rev()))
 379                 .all(|(x, y)| x.has_overlapping_values(y)),
 380
 381             // Enums can mix unit variants with tuple/struct variants. These can never overlap.
 382             (Self::Path(_), Self::Tuple(..) | Self::Struct(..))
 383             | (Self::Tuple(..) | Self::Struct(..), Self::Path(_)) => false,
 384
 385             // Tuples can be matched like a struct.
 386             (Self::Tuple(x, _), Self::Struct(y, _)) | (Self::Struct(x, _), Self::Tuple(y, _)) => {
 387                 // TODO: check fields here.
 388                 x == y
 389             },
 390
 391             // TODO: Lit* with Path, Range with Path, LitBytes with Slice
 392             _ => true,
 393         }
 394     }
 395 }
 396
 397 fn pat_contains_local(pat: &Pat<'_>, id: HirId) -> bool {
 398     let mut result = false;
 399     pat.walk_short(|p| {
 400         result |= matches!(p.kind, PatKind::Binding(_, binding_id, ..) if binding_id == id);
 401         !result
 402     });
 403     result
 404 }
 405
 406 /// Returns true if all the bindings in the `Pat` are in `ids` and vice versa
 407 fn bindings_eq(pat: &Pat<'_>, mut ids: HirIdSet) -> bool {
 408     let mut result = true;
 409     pat.each_binding_or_first(&mut |_, id, _, _| result &= ids.remove(&id));
 410     result && ids.is_empty()
 411 }