1 use super::NEEDLESS_RANGE_LOOP;
2 use crate::utils::visitors::LocalUsedVisitor;
4 contains_name, has_iter_method, higher, is_integer_const, match_trait_method, multispan_sugg, path_to_local_id,
5 paths, snippet, span_lint_and_then, sugg, SpanlessEq,
7 use if_chain::if_chain;
9 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
10 use rustc_hir::def::{DefKind, Res};
11 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
12 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath};
13 use rustc_lint::LateContext;
14 use rustc_middle::hir::map::Map;
15 use rustc_middle::middle::region;
16 use rustc_middle::ty::{self, Ty};
17 use rustc_span::symbol::{sym, Symbol};
18 use std::iter::Iterator;
21 /// Checks for looping over a range and then indexing a sequence with it.
22 /// The iteratee must be a range literal.
23 #[allow(clippy::too_many_lines)]
24 pub(super) fn check<'tcx>(
25 cx: &LateContext<'tcx>,
31 if let Some(higher::Range {
35 }) = higher::range(arg)
37 // the var must be a single name
38 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
39 let mut visitor = VarVisitor {
42 indexed_mut: FxHashSet::default(),
43 indexed_indirectly: FxHashMap::default(),
44 indexed_directly: FxHashMap::default(),
45 referenced: FxHashSet::default(),
47 prefer_mutable: false,
49 walk_expr(&mut visitor, body);
51 // linting condition: we only indexed one variable, and indexed it directly
52 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
53 let (indexed, (indexed_extent, indexed_ty)) = visitor
57 .expect("already checked that we have exactly 1 element");
59 // ensure that the indexed variable was declared before the loop, see #601
60 if let Some(indexed_extent) = indexed_extent {
61 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
62 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
63 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
64 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
65 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
70 // don't lint if the container that is indexed does not have .iter() method
71 let has_iter = has_iter_method(cx, indexed_ty);
72 if has_iter.is_none() {
76 // don't lint if the container that is indexed into is also used without
78 if visitor.referenced.contains(&indexed) {
82 let starts_at_zero = is_integer_const(cx, start, 0);
84 let skip = if starts_at_zero {
86 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
89 format!(".skip({})", snippet(cx, start.span, ".."))
92 let mut end_is_start_plus_val = false;
94 let take = if let Some(end) = *end {
95 let mut take_expr = end;
97 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
98 if let BinOpKind::Add = op.node {
99 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
100 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
102 if start_equal_left {
104 } else if start_equal_right {
108 end_is_start_plus_val = start_equal_left | start_equal_right;
112 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
114 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
118 ast::RangeLimits::Closed => {
119 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
120 format!(".take({})", take_expr + sugg::ONE)
122 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
129 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
135 let take_is_empty = take.is_empty();
136 let mut method_1 = take;
137 let mut method_2 = skip;
139 if end_is_start_plus_val {
140 mem::swap(&mut method_1, &mut method_2);
143 if visitor.nonindex {
148 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
152 "consider using an iterator",
154 (pat.span, format!("({}, <item>)", ident.name)),
157 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
164 let repl = if starts_at_zero && take_is_empty {
165 format!("&{}{}", ref_mut, indexed)
167 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
174 &format!("the loop variable `{}` is only used to index `{}`", ident.name, indexed),
178 "consider using an iterator",
179 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
189 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
191 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
192 if len_args.len() == 1;
193 if method.ident.name == sym!(len);
194 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
195 if path.segments.len() == 1;
196 if path.segments[0].ident.name == var;
205 fn is_end_eq_array_len<'tcx>(
206 cx: &LateContext<'tcx>,
208 limits: ast::RangeLimits,
209 indexed_ty: Ty<'tcx>,
212 if let ExprKind::Lit(ref lit) = end.kind;
213 if let ast::LitKind::Int(end_int, _) = lit.node;
214 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
215 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
217 return match limits {
218 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
219 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
227 struct VarVisitor<'a, 'tcx> {
228 /// context reference
229 cx: &'a LateContext<'tcx>,
230 /// var name to look for as index
232 /// indexed variables that are used mutably
233 indexed_mut: FxHashSet<Symbol>,
234 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
235 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
236 /// subset of `indexed` of vars that are indexed directly: `v[i]`
237 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
238 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
239 /// Any names that are used outside an index operation.
240 /// Used to detect things like `&mut vec` used together with `vec[i]`
241 referenced: FxHashSet<Symbol>,
242 /// has the loop variable been used in expressions other than the index of
245 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
246 /// takes `&mut self`
247 prefer_mutable: bool,
250 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
251 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
253 // the indexed container is referenced by a name
254 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
255 if let QPath::Resolved(None, ref seqvar) = *seqpath;
256 if seqvar.segments.len() == 1;
258 let index_used_directly = path_to_local_id(idx, self.var);
259 let indexed_indirectly = {
260 let mut used_visitor = LocalUsedVisitor::new(self.cx, self.var);
261 walk_expr(&mut used_visitor, idx);
265 if indexed_indirectly || index_used_directly {
266 if self.prefer_mutable {
267 self.indexed_mut.insert(seqvar.segments[0].ident.name);
269 let res = self.cx.qpath_res(seqpath, seqexpr.hir_id);
271 Res::Local(hir_id) => {
272 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
273 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
274 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
275 if indexed_indirectly {
276 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
278 if index_used_directly {
279 self.indexed_directly.insert(
280 seqvar.segments[0].ident.name,
281 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
284 return false; // no need to walk further *on the variable*
286 Res::Def(DefKind::Static | DefKind::Const, ..) => {
287 if indexed_indirectly {
288 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
290 if index_used_directly {
291 self.indexed_directly.insert(
292 seqvar.segments[0].ident.name,
293 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
296 return false; // no need to walk further *on the variable*
307 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
308 type Map = Map<'tcx>;
310 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
313 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
314 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
315 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
316 if !self.check(&args[1], &args[0], expr);
322 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
323 if !self.check(idx, seqexpr, expr);
328 // directly using a variable
329 if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind;
330 if let Res::Local(local_id) = path.res;
332 if local_id == self.var {
333 self.nonindex = true;
335 // not the correct variable, but still a variable
336 self.referenced.insert(path.segments[0].ident.name);
341 let old = self.prefer_mutable;
343 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
344 self.prefer_mutable = true;
345 self.visit_expr(lhs);
346 self.prefer_mutable = false;
347 self.visit_expr(rhs);
349 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
350 if mutbl == Mutability::Mut {
351 self.prefer_mutable = true;
353 self.visit_expr(expr);
355 ExprKind::Call(ref f, args) => {
358 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
359 self.prefer_mutable = false;
360 if let ty::Ref(_, _, mutbl) = *ty.kind() {
361 if mutbl == Mutability::Mut {
362 self.prefer_mutable = true;
365 self.visit_expr(expr);
368 ExprKind::MethodCall(_, _, args, _) => {
369 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
370 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
371 self.prefer_mutable = false;
372 if let ty::Ref(_, _, mutbl) = *ty.kind() {
373 if mutbl == Mutability::Mut {
374 self.prefer_mutable = true;
377 self.visit_expr(expr);
380 ExprKind::Closure(_, _, body_id, ..) => {
381 let body = self.cx.tcx.hir().body(body_id);
382 self.visit_expr(&body.value);
384 _ => walk_expr(self, expr),
386 self.prefer_mutable = old;
388 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
389 NestedVisitorMap::None