src/tools/clippy/clippy_lints/src/loops/manual_memcpy.rs

   1 use super::{get_span_of_entire_for_loop, IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
   2 use crate::utils::sugg::Sugg;
   3 use crate::utils::{
   4     get_enclosing_block, higher, is_type_diagnostic_item, path_to_local, snippet, span_lint_and_sugg, sugg,
   5 };
   6 use if_chain::if_chain;
   7 use rustc_ast::ast;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::intravisit::walk_block;
  10 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, Pat, PatKind, StmtKind};
  11 use rustc_lint::LateContext;
  12 use rustc_middle::ty::{self, Ty};
  13 use rustc_span::symbol::sym;
  14 use std::iter::Iterator;
  15
  16 /// Checks for for loops that sequentially copy items from one slice-like
  17 /// object to another.
  18 pub(super) fn check<'tcx>(
  19     cx: &LateContext<'tcx>,
  20     pat: &'tcx Pat<'_>,
  21     arg: &'tcx Expr<'_>,
  22     body: &'tcx Expr<'_>,
  23     expr: &'tcx Expr<'_>,
  24 ) -> bool {
  25     if let Some(higher::Range {
  26         start: Some(start),
  27         end: Some(end),
  28         limits,
  29     }) = higher::range(arg)
  30     {
  31         // the var must be a single name
  32         if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
  33             let mut starts = vec![Start {
  34                 id: canonical_id,
  35                 kind: StartKind::Range,
  36             }];
  37
  38             // This is one of few ways to return different iterators
  39             // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
  40             let mut iter_a = None;
  41             let mut iter_b = None;
  42
  43             if let ExprKind::Block(block, _) = body.kind {
  44                 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
  45                     starts.extend(loop_counters);
  46                 }
  47                 iter_a = Some(get_assignments(block, &starts));
  48             } else {
  49                 iter_b = Some(get_assignment(body));
  50             }
  51
  52             let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
  53
  54             let big_sugg = assignments
  55                 // The only statements in the for loops can be indexed assignments from
  56                 // indexed retrievals (except increments of loop counters).
  57                 .map(|o| {
  58                     o.and_then(|(lhs, rhs)| {
  59                         let rhs = fetch_cloned_expr(rhs);
  60                         if_chain! {
  61                             if let ExprKind::Index(base_left, idx_left) = lhs.kind;
  62                             if let ExprKind::Index(base_right, idx_right) = rhs.kind;
  63                             if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
  64                                 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
  65                             if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
  66                             if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
  67
  68                             // Source and destination must be different
  69                             if path_to_local(base_left) != path_to_local(base_right);
  70                             then {
  71                                 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
  72                                     IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
  73                             } else {
  74                                 None
  75                             }
  76                         }
  77                     })
  78                 })
  79                 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
  80                 .collect::<Option<Vec<_>>>()
  81                 .filter(|v| !v.is_empty())
  82                 .map(|v| v.join("\n    "));
  83
  84             if let Some(big_sugg) = big_sugg {
  85                 span_lint_and_sugg(
  86                     cx,
  87                     MANUAL_MEMCPY,
  88                     get_span_of_entire_for_loop(expr),
  89                     "it looks like you're manually copying between slices",
  90                     "try replacing the loop by",
  91                     big_sugg,
  92                     Applicability::Unspecified,
  93                 );
  94                 return true;
  95             }
  96         }
  97     }
  98     false
  99 }
 100
 101 fn build_manual_memcpy_suggestion<'tcx>(
 102     cx: &LateContext<'tcx>,
 103     start: &Expr<'_>,
 104     end: &Expr<'_>,
 105     limits: ast::RangeLimits,
 106     dst: &IndexExpr<'_>,
 107     src: &IndexExpr<'_>,
 108 ) -> String {
 109     fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
 110         if offset.as_str() == "0" {
 111             sugg::EMPTY.into()
 112         } else {
 113             offset
 114         }
 115     }
 116
 117     let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
 118         if_chain! {
 119             if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
 120             if method.ident.name == sym!(len);
 121             if len_args.len() == 1;
 122             if let Some(arg) = len_args.get(0);
 123             if path_to_local(arg) == path_to_local(base);
 124             then {
 125                 if sugg.as_str() == end_str {
 126                     sugg::EMPTY.into()
 127                 } else {
 128                     sugg
 129                 }
 130             } else {
 131                 match limits {
 132                     ast::RangeLimits::Closed => {
 133                         sugg + &sugg::ONE.into()
 134                     },
 135                     ast::RangeLimits::HalfOpen => sugg,
 136                 }
 137             }
 138         }
 139     };
 140
 141     let start_str = Sugg::hir(cx, start, "").into();
 142     let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
 143
 144     let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
 145         StartKind::Range => (
 146             print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
 147             print_limit(
 148                 end,
 149                 end_str.as_str(),
 150                 idx_expr.base,
 151                 apply_offset(&end_str, &idx_expr.idx_offset),
 152             )
 153             .into_sugg(),
 154         ),
 155         StartKind::Counter { initializer } => {
 156             let counter_start = Sugg::hir(cx, initializer, "").into();
 157             (
 158                 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
 159                 print_limit(
 160                     end,
 161                     end_str.as_str(),
 162                     idx_expr.base,
 163                     apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
 164                 )
 165                 .into_sugg(),
 166             )
 167         },
 168     };
 169
 170     let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
 171     let (src_offset, src_limit) = print_offset_and_limit(&src);
 172
 173     let dst_base_str = snippet(cx, dst.base.span, "???");
 174     let src_base_str = snippet(cx, src.base.span, "???");
 175
 176     let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
 177         dst_base_str
 178     } else {
 179         format!(
 180             "{}[{}..{}]",
 181             dst_base_str,
 182             dst_offset.maybe_par(),
 183             dst_limit.maybe_par()
 184         )
 185         .into()
 186     };
 187
 188     format!(
 189         "{}.clone_from_slice(&{}[{}..{}]);",
 190         dst,
 191         src_base_str,
 192         src_offset.maybe_par(),
 193         src_limit.maybe_par()
 194     )
 195 }
 196
 197 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
 198 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
 199 /// it exists for the convenience of the overloaded operators while normal functions can do the
 200 /// same.
 201 #[derive(Clone)]
 202 struct MinifyingSugg<'a>(Sugg<'a>);
 203
 204 impl<'a> MinifyingSugg<'a> {
 205     fn as_str(&self) -> &str {
 206         // HACK: Don't sync to Clippy! Required because something with the `or_patterns` feature
 207         // changed and this would now require parentheses.
 208         match &self.0 {
 209             Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) => s.as_ref(),
 210         }
 211     }
 212
 213     fn into_sugg(self) -> Sugg<'a> {
 214         self.0
 215     }
 216 }
 217
 218 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
 219     fn from(sugg: Sugg<'a>) -> Self {
 220         Self(sugg)
 221     }
 222 }
 223
 224 impl std::ops::Add for &MinifyingSugg<'static> {
 225     type Output = MinifyingSugg<'static>;
 226     fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
 227         match (self.as_str(), rhs.as_str()) {
 228             ("0", _) => rhs.clone(),
 229             (_, "0") => self.clone(),
 230             (_, _) => (&self.0 + &rhs.0).into(),
 231         }
 232     }
 233 }
 234
 235 impl std::ops::Sub for &MinifyingSugg<'static> {
 236     type Output = MinifyingSugg<'static>;
 237     fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
 238         match (self.as_str(), rhs.as_str()) {
 239             (_, "0") => self.clone(),
 240             ("0", _) => (-rhs.0.clone()).into(),
 241             (x, y) if x == y => sugg::ZERO.into(),
 242             (_, _) => (&self.0 - &rhs.0).into(),
 243         }
 244     }
 245 }
 246
 247 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
 248     type Output = MinifyingSugg<'static>;
 249     fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
 250         match (self.as_str(), rhs.as_str()) {
 251             ("0", _) => rhs.clone(),
 252             (_, "0") => self,
 253             (_, _) => (self.0 + &rhs.0).into(),
 254         }
 255     }
 256 }
 257
 258 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
 259     type Output = MinifyingSugg<'static>;
 260     fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
 261         match (self.as_str(), rhs.as_str()) {
 262             (_, "0") => self,
 263             ("0", _) => (-rhs.0.clone()).into(),
 264             (x, y) if x == y => sugg::ZERO.into(),
 265             (_, _) => (self.0 - &rhs.0).into(),
 266         }
 267     }
 268 }
 269
 270 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
 271 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
 272 struct Offset {
 273     value: MinifyingSugg<'static>,
 274     sign: OffsetSign,
 275 }
 276
 277 #[derive(Clone, Copy)]
 278 enum OffsetSign {
 279     Positive,
 280     Negative,
 281 }
 282
 283 impl Offset {
 284     fn negative(value: Sugg<'static>) -> Self {
 285         Self {
 286             value: value.into(),
 287             sign: OffsetSign::Negative,
 288         }
 289     }
 290
 291     fn positive(value: Sugg<'static>) -> Self {
 292         Self {
 293             value: value.into(),
 294             sign: OffsetSign::Positive,
 295         }
 296     }
 297
 298     fn empty() -> Self {
 299         Self::positive(sugg::ZERO)
 300     }
 301 }
 302
 303 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
 304     match rhs.sign {
 305         OffsetSign::Positive => lhs + &rhs.value,
 306         OffsetSign::Negative => lhs - &rhs.value,
 307     }
 308 }
 309
 310 #[derive(Debug, Clone, Copy)]
 311 enum StartKind<'hir> {
 312     Range,
 313     Counter { initializer: &'hir Expr<'hir> },
 314 }
 315
 316 struct IndexExpr<'hir> {
 317     base: &'hir Expr<'hir>,
 318     idx: StartKind<'hir>,
 319     idx_offset: Offset,
 320 }
 321
 322 struct Start<'hir> {
 323     id: HirId,
 324     kind: StartKind<'hir>,
 325 }
 326
 327 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
 328     let is_slice = match ty.kind() {
 329         ty::Ref(_, subty, _) => is_slice_like(cx, subty),
 330         ty::Slice(..) | ty::Array(..) => true,
 331         _ => false,
 332     };
 333
 334     is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym::vecdeque_type)
 335 }
 336
 337 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
 338     if_chain! {
 339         if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
 340         if method.ident.name == sym::clone;
 341         if args.len() == 1;
 342         if let Some(arg) = args.get(0);
 343         then { arg } else { expr }
 344     }
 345 }
 346
 347 fn get_details_from_idx<'tcx>(
 348     cx: &LateContext<'tcx>,
 349     idx: &Expr<'_>,
 350     starts: &[Start<'tcx>],
 351 ) -> Option<(StartKind<'tcx>, Offset)> {
 352     fn get_start<'tcx>(e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
 353         let id = path_to_local(e)?;
 354         starts.iter().find(|start| start.id == id).map(|start| start.kind)
 355     }
 356
 357     fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
 358         match &e.kind {
 359             ExprKind::Lit(l) => match l.node {
 360                 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
 361                 _ => None,
 362             },
 363             ExprKind::Path(..) if get_start(e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
 364             _ => None,
 365         }
 366     }
 367
 368     match idx.kind {
 369         ExprKind::Binary(op, lhs, rhs) => match op.node {
 370             BinOpKind::Add => {
 371                 let offset_opt = get_start(lhs, starts)
 372                     .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
 373                     .or_else(|| get_start(rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
 374
 375                 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
 376             },
 377             BinOpKind::Sub => {
 378                 get_start(lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
 379             },
 380             _ => None,
 381         },
 382         ExprKind::Path(..) => get_start(idx, starts).map(|s| (s, Offset::empty())),
 383         _ => None,
 384     }
 385 }
 386
 387 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
 388     if let ExprKind::Assign(lhs, rhs, _) = e.kind {
 389         Some((lhs, rhs))
 390     } else {
 391         None
 392     }
 393 }
 394
 395 /// Get assignments from the given block.
 396 /// The returned iterator yields `None` if no assignment expressions are there,
 397 /// filtering out the increments of the given whitelisted loop counters;
 398 /// because its job is to make sure there's nothing other than assignments and the increments.
 399 fn get_assignments<'a, 'tcx>(
 400     Block { stmts, expr, .. }: &'tcx Block<'tcx>,
 401     loop_counters: &'a [Start<'tcx>],
 402 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'a {
 403     // As the `filter` and `map` below do different things, I think putting together
 404     // just increases complexity. (cc #3188 and #4193)
 405     stmts
 406         .iter()
 407         .filter_map(move |stmt| match stmt.kind {
 408             StmtKind::Local(..) | StmtKind::Item(..) => None,
 409             StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
 410         })
 411         .chain((*expr).into_iter())
 412         .filter(move |e| {
 413             if let ExprKind::AssignOp(_, place, _) = e.kind {
 414                 path_to_local(place).map_or(false, |id| {
 415                     !loop_counters
 416                         .iter()
 417                         // skip the first item which should be `StartKind::Range`
 418                         // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
 419                         .skip(1)
 420                         .any(|counter| counter.id == id)
 421                 })
 422             } else {
 423                 true
 424             }
 425         })
 426         .map(get_assignment)
 427 }
 428
 429 fn get_loop_counters<'a, 'tcx>(
 430     cx: &'a LateContext<'tcx>,
 431     body: &'tcx Block<'tcx>,
 432     expr: &'tcx Expr<'_>,
 433 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
 434     // Look for variables that are incremented once per loop iteration.
 435     let mut increment_visitor = IncrementVisitor::new(cx);
 436     walk_block(&mut increment_visitor, body);
 437
 438     // For each candidate, check the parent block to see if
 439     // it's initialized to zero at the start of the loop.
 440     get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
 441         increment_visitor
 442             .into_results()
 443             .filter_map(move |var_id| {
 444                 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
 445                 walk_block(&mut initialize_visitor, block);
 446
 447                 initialize_visitor.get_result().map(|(_, initializer)| Start {
 448                     id: var_id,
 449                     kind: StartKind::Counter { initializer },
 450                 })
 451             })
 452             .into()
 453     })
 454 }