clippy_lints/src/loops/needless_collect.rs

   1 use crate::utils::sugg::Sugg;
   2 use crate::utils::{
   3     is_type_diagnostic_item, match_trait_method, match_type, path_to_local_id, paths, snippet, span_lint_and_sugg,
   4     span_lint_and_then,
   5 };
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor};
   9 use rustc_hir::{Block, Expr, ExprKind, GenericArg, HirId, Local, Pat, PatKind, QPath, StmtKind};
  10 use rustc_lint::LateContext;
  11 use rustc_middle::hir::map::Map;
  12 use rustc_span::source_map::Span;
  13 use rustc_span::symbol::{sym, Ident};
  14
  15 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
  16
  17 pub(super) fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  18     check_needless_collect_direct_usage(expr, cx);
  19     check_needless_collect_indirect_usage(expr, cx);
  20 }
  21 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  22     if_chain! {
  23         if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
  24         if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
  25         if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
  26         if let Some(ref generic_args) = chain_method.args;
  27         if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
  28         then {
  29             let ty = cx.typeck_results().node_type(ty.hir_id);
  30             if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
  31                 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
  32                 match_type(cx, ty, &paths::BTREEMAP) ||
  33                 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
  34                 if method.ident.name == sym!(len) {
  35                     let span = shorten_needless_collect_span(expr);
  36                     span_lint_and_sugg(
  37                         cx,
  38                         super::NEEDLESS_COLLECT,
  39                         span,
  40                         NEEDLESS_COLLECT_MSG,
  41                         "replace with",
  42                         "count()".to_string(),
  43                         Applicability::MachineApplicable,
  44                     );
  45                 }
  46                 if method.ident.name == sym!(is_empty) {
  47                     let span = shorten_needless_collect_span(expr);
  48                     span_lint_and_sugg(
  49                         cx,
  50                         super::NEEDLESS_COLLECT,
  51                         span,
  52                         NEEDLESS_COLLECT_MSG,
  53                         "replace with",
  54                         "next().is_none()".to_string(),
  55                         Applicability::MachineApplicable,
  56                     );
  57                 }
  58                 if method.ident.name == sym!(contains) {
  59                     let contains_arg = snippet(cx, args[1].span, "??");
  60                     let span = shorten_needless_collect_span(expr);
  61                     span_lint_and_then(
  62                         cx,
  63                         super::NEEDLESS_COLLECT,
  64                         span,
  65                         NEEDLESS_COLLECT_MSG,
  66                         |diag| {
  67                             let (arg, pred) = contains_arg
  68                                     .strip_prefix('&')
  69                                     .map_or(("&x", &*contains_arg), |s| ("x", s));
  70                             diag.span_suggestion(
  71                                 span,
  72                                 "replace with",
  73                                 format!(
  74                                     "any(|{}| x == {})",
  75                                     arg, pred
  76                                 ),
  77                                 Applicability::MachineApplicable,
  78                             );
  79                         }
  80                     );
  81                 }
  82             }
  83         }
  84     }
  85 }
  86
  87 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  88     if let ExprKind::Block(ref block, _) = expr.kind {
  89         for ref stmt in block.stmts {
  90             if_chain! {
  91                 if let StmtKind::Local(
  92                     Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
  93                     init: Some(ref init_expr), .. }
  94                 ) = stmt.kind;
  95                 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
  96                 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
  97                 if let Some(ref generic_args) = method_name.args;
  98                 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
  99                 if let ty = cx.typeck_results().node_type(ty.hir_id);
 100                 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
 101                     is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
 102                     match_type(cx, ty, &paths::LINKED_LIST);
 103                 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
 104                 if iter_calls.len() == 1;
 105                 then {
 106                     let mut used_count_visitor = UsedCountVisitor {
 107                         cx,
 108                         id: *pat_id,
 109                         count: 0,
 110                     };
 111                     walk_block(&mut used_count_visitor, block);
 112                     if used_count_visitor.count > 1 {
 113                         return;
 114                     }
 115
 116                     // Suggest replacing iter_call with iter_replacement, and removing stmt
 117                     let iter_call = &iter_calls[0];
 118                     span_lint_and_then(
 119                         cx,
 120                         super::NEEDLESS_COLLECT,
 121                         stmt.span.until(iter_call.span),
 122                         NEEDLESS_COLLECT_MSG,
 123                         |diag| {
 124                             let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
 125                             diag.multipart_suggestion(
 126                                 iter_call.get_suggestion_text(),
 127                                 vec![
 128                                     (stmt.span, String::new()),
 129                                     (iter_call.span, iter_replacement)
 130                                 ],
 131                                 Applicability::MachineApplicable,// MaybeIncorrect,
 132                             ).emit();
 133                         },
 134                     );
 135                 }
 136             }
 137         }
 138     }
 139 }
 140
 141 struct IterFunction {
 142     func: IterFunctionKind,
 143     span: Span,
 144 }
 145 impl IterFunction {
 146     fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
 147         match &self.func {
 148             IterFunctionKind::IntoIter => String::new(),
 149             IterFunctionKind::Len => String::from(".count()"),
 150             IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
 151             IterFunctionKind::Contains(span) => {
 152                 let s = snippet(cx, *span, "..");
 153                 if let Some(stripped) = s.strip_prefix('&') {
 154                     format!(".any(|x| x == {})", stripped)
 155                 } else {
 156                     format!(".any(|x| x == *{})", s)
 157                 }
 158             },
 159         }
 160     }
 161     fn get_suggestion_text(&self) -> &'static str {
 162         match &self.func {
 163             IterFunctionKind::IntoIter => {
 164                 "use the original Iterator instead of collecting it and then producing a new one"
 165             },
 166             IterFunctionKind::Len => {
 167                 "take the original Iterator's count instead of collecting it and finding the length"
 168             },
 169             IterFunctionKind::IsEmpty => {
 170                 "check if the original Iterator has anything instead of collecting it and seeing if it's empty"
 171             },
 172             IterFunctionKind::Contains(_) => {
 173                 "check if the original Iterator contains an element instead of collecting then checking"
 174             },
 175         }
 176     }
 177 }
 178 enum IterFunctionKind {
 179     IntoIter,
 180     Len,
 181     IsEmpty,
 182     Contains(Span),
 183 }
 184
 185 struct IterFunctionVisitor {
 186     uses: Vec<IterFunction>,
 187     seen_other: bool,
 188     target: Ident,
 189 }
 190 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
 191     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
 192         // Check function calls on our collection
 193         if_chain! {
 194             if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
 195             if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
 196             if let &[name] = &path.segments;
 197             if name.ident == self.target;
 198             then {
 199                 let len = sym!(len);
 200                 let is_empty = sym!(is_empty);
 201                 let contains = sym!(contains);
 202                 match method_name.ident.name {
 203                     sym::into_iter => self.uses.push(
 204                         IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
 205                     ),
 206                     name if name == len => self.uses.push(
 207                         IterFunction { func: IterFunctionKind::Len, span: expr.span }
 208                     ),
 209                     name if name == is_empty => self.uses.push(
 210                         IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
 211                     ),
 212                     name if name == contains => self.uses.push(
 213                         IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
 214                     ),
 215                     _ => self.seen_other = true,
 216                 }
 217                 return
 218             }
 219         }
 220         // Check if the collection is used for anything else
 221         if_chain! {
 222             if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
 223             if let &[name] = &path.segments;
 224             if name.ident == self.target;
 225             then {
 226                 self.seen_other = true;
 227             } else {
 228                 walk_expr(self, expr);
 229             }
 230         }
 231     }
 232
 233     type Map = Map<'tcx>;
 234     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 235         NestedVisitorMap::None
 236     }
 237 }
 238
 239 struct UsedCountVisitor<'a, 'tcx> {
 240     cx: &'a LateContext<'tcx>,
 241     id: HirId,
 242     count: usize,
 243 }
 244
 245 impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
 246     type Map = Map<'tcx>;
 247
 248     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 249         if path_to_local_id(expr, self.id) {
 250             self.count += 1;
 251         } else {
 252             walk_expr(self, expr);
 253         }
 254     }
 255
 256     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 257         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
 258     }
 259 }
 260
 261 /// Detect the occurrences of calls to `iter` or `into_iter` for the
 262 /// given identifier
 263 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
 264     let mut visitor = IterFunctionVisitor {
 265         uses: Vec::new(),
 266         target: identifier,
 267         seen_other: false,
 268     };
 269     visitor.visit_block(block);
 270     if visitor.seen_other { None } else { Some(visitor.uses) }
 271 }
 272
 273 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
 274     if_chain! {
 275         if let ExprKind::MethodCall(.., args, _) = &expr.kind;
 276         if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
 277         then {
 278             return expr.span.with_lo(span.lo());
 279         }
 280     }
 281     unreachable!();
 282 }