clippy_lints/src/loops/needless_collect.rs

   1 use super::NEEDLESS_COLLECT;
   2 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
   3 use clippy_utils::source::snippet;
   4 use clippy_utils::sugg::Sugg;
   5 use clippy_utils::ty::{is_type_diagnostic_item, match_type};
   6 use clippy_utils::{is_trait_method, path_to_local_id, paths};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor};
  10 use rustc_hir::{Block, Expr, ExprKind, GenericArg, HirId, Local, Pat, PatKind, QPath, StmtKind};
  11 use rustc_lint::LateContext;
  12 use rustc_middle::hir::map::Map;
  13 use rustc_span::symbol::{sym, Ident};
  14 use rustc_span::{MultiSpan, Span};
  15
  16 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
  17
  18 pub(super) fn check<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  19     check_needless_collect_direct_usage(expr, cx);
  20     check_needless_collect_indirect_usage(expr, cx);
  21 }
  22 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  23     if_chain! {
  24         if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
  25         if let ExprKind::MethodCall(chain_method, method0_span, _, _) = args[0].kind;
  26         if chain_method.ident.name == sym!(collect) && is_trait_method(cx, &args[0], sym::Iterator);
  27         if let Some(generic_args) = chain_method.args;
  28         if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
  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 let Some(sugg) = match &*method.ident.name.as_str() {
  35             "len" => Some("count()".to_string()),
  36             "is_empty" => Some("next().is_none()".to_string()),
  37             "contains" => {
  38                 let contains_arg = snippet(cx, args[1].span, "??");
  39                 let (arg, pred) = contains_arg
  40                     .strip_prefix('&')
  41                     .map_or(("&x", &*contains_arg), |s| ("x", s));
  42                 Some(format!("any(|{}| x == {})", arg, pred))
  43             }
  44             _ => None,
  45         };
  46         then {
  47             span_lint_and_sugg(
  48                 cx,
  49                 NEEDLESS_COLLECT,
  50                 method0_span.with_hi(expr.span.hi()),
  51                 NEEDLESS_COLLECT_MSG,
  52                 "replace with",
  53                 sugg,
  54                 Applicability::MachineApplicable,
  55             );
  56         }
  57     }
  58 }
  59
  60 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
  61     if let ExprKind::Block(block, _) = expr.kind {
  62         for stmt in block.stmts {
  63             if_chain! {
  64                 if let StmtKind::Local(
  65                     Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
  66                     init: Some(init_expr), .. }
  67                 ) = stmt.kind;
  68                 if let ExprKind::MethodCall(method_name, collect_span, &[ref iter_source], ..) = init_expr.kind;
  69                 if method_name.ident.name == sym!(collect) && is_trait_method(cx, init_expr, sym::Iterator);
  70                 if let Some(generic_args) = method_name.args;
  71                 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
  72                 if let ty = cx.typeck_results().node_type(ty.hir_id);
  73                 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
  74                     is_type_diagnostic_item(cx, ty, sym::vecdeque_type) ||
  75                     match_type(cx, ty, &paths::LINKED_LIST);
  76                 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
  77                 if let [iter_call] = &*iter_calls;
  78                 then {
  79                     let mut used_count_visitor = UsedCountVisitor {
  80                         cx,
  81                         id: *pat_id,
  82                         count: 0,
  83                     };
  84                     walk_block(&mut used_count_visitor, block);
  85                     if used_count_visitor.count > 1 {
  86                         return;
  87                     }
  88
  89                     // Suggest replacing iter_call with iter_replacement, and removing stmt
  90                     let mut span = MultiSpan::from_span(collect_span);
  91                     span.push_span_label(iter_call.span, "the iterator could be used here instead".into());
  92                     span_lint_and_then(
  93                         cx,
  94                         super::NEEDLESS_COLLECT,
  95                         span,
  96                         NEEDLESS_COLLECT_MSG,
  97                         |diag| {
  98                             let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
  99                             diag.multipart_suggestion(
 100                                 iter_call.get_suggestion_text(),
 101                                 vec![
 102                                     (stmt.span, String::new()),
 103                                     (iter_call.span, iter_replacement)
 104                                 ],
 105                                 Applicability::MachineApplicable,// MaybeIncorrect,
 106                             );
 107                         },
 108                     );
 109                 }
 110             }
 111         }
 112     }
 113 }
 114
 115 struct IterFunction {
 116     func: IterFunctionKind,
 117     span: Span,
 118 }
 119 impl IterFunction {
 120     fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
 121         match &self.func {
 122             IterFunctionKind::IntoIter => String::new(),
 123             IterFunctionKind::Len => String::from(".count()"),
 124             IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
 125             IterFunctionKind::Contains(span) => {
 126                 let s = snippet(cx, *span, "..");
 127                 if let Some(stripped) = s.strip_prefix('&') {
 128                     format!(".any(|x| x == {})", stripped)
 129                 } else {
 130                     format!(".any(|x| x == *{})", s)
 131                 }
 132             },
 133         }
 134     }
 135     fn get_suggestion_text(&self) -> &'static str {
 136         match &self.func {
 137             IterFunctionKind::IntoIter => {
 138                 "use the original Iterator instead of collecting it and then producing a new one"
 139             },
 140             IterFunctionKind::Len => {
 141                 "take the original Iterator's count instead of collecting it and finding the length"
 142             },
 143             IterFunctionKind::IsEmpty => {
 144                 "check if the original Iterator has anything instead of collecting it and seeing if it's empty"
 145             },
 146             IterFunctionKind::Contains(_) => {
 147                 "check if the original Iterator contains an element instead of collecting then checking"
 148             },
 149         }
 150     }
 151 }
 152 enum IterFunctionKind {
 153     IntoIter,
 154     Len,
 155     IsEmpty,
 156     Contains(Span),
 157 }
 158
 159 struct IterFunctionVisitor {
 160     uses: Vec<IterFunction>,
 161     seen_other: bool,
 162     target: Ident,
 163 }
 164 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
 165     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
 166         // Check function calls on our collection
 167         if_chain! {
 168             if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
 169             if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, path)), .. }) = args.get(0);
 170             if let &[name] = &path.segments;
 171             if name.ident == self.target;
 172             then {
 173                 let len = sym!(len);
 174                 let is_empty = sym!(is_empty);
 175                 let contains = sym!(contains);
 176                 match method_name.ident.name {
 177                     sym::into_iter => self.uses.push(
 178                         IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
 179                     ),
 180                     name if name == len => self.uses.push(
 181                         IterFunction { func: IterFunctionKind::Len, span: expr.span }
 182                     ),
 183                     name if name == is_empty => self.uses.push(
 184                         IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
 185                     ),
 186                     name if name == contains => self.uses.push(
 187                         IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
 188                     ),
 189                     _ => self.seen_other = true,
 190                 }
 191                 return
 192             }
 193         }
 194         // Check if the collection is used for anything else
 195         if_chain! {
 196             if let Expr { kind: ExprKind::Path(QPath::Resolved(_, path)), .. } = expr;
 197             if let &[name] = &path.segments;
 198             if name.ident == self.target;
 199             then {
 200                 self.seen_other = true;
 201             } else {
 202                 walk_expr(self, expr);
 203             }
 204         }
 205     }
 206
 207     type Map = Map<'tcx>;
 208     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 209         NestedVisitorMap::None
 210     }
 211 }
 212
 213 struct UsedCountVisitor<'a, 'tcx> {
 214     cx: &'a LateContext<'tcx>,
 215     id: HirId,
 216     count: usize,
 217 }
 218
 219 impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
 220     type Map = Map<'tcx>;
 221
 222     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 223         if path_to_local_id(expr, self.id) {
 224             self.count += 1;
 225         } else {
 226             walk_expr(self, expr);
 227         }
 228     }
 229
 230     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 231         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
 232     }
 233 }
 234
 235 /// Detect the occurrences of calls to `iter` or `into_iter` for the
 236 /// given identifier
 237 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
 238     let mut visitor = IterFunctionVisitor {
 239         uses: Vec::new(),
 240         target: identifier,
 241         seen_other: false,
 242     };
 243     visitor.visit_block(block);
 244     if visitor.seen_other { None } else { Some(visitor.uses) }
 245 }