1 use super::WHILE_LET_ON_ITERATOR;
2 use clippy_utils::diagnostics::span_lint_and_sugg;
3 use clippy_utils::source::snippet_with_applicability;
5 get_enclosing_loop_or_closure, is_refutable, is_trait_method, match_def_path, paths, visitors::is_res_used,
7 use if_chain::if_chain;
8 use rustc_errors::Applicability;
9 use rustc_hir::intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor};
10 use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, MatchSource, Mutability, Node, PatKind, QPath, UnOp};
11 use rustc_lint::LateContext;
12 use rustc_span::{symbol::sym, Span, Symbol};
14 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
15 let (scrutinee_expr, iter_expr, some_pat, loop_expr) = if_chain! {
16 if let ExprKind::Match(scrutinee_expr, [arm, _], MatchSource::WhileLetDesugar) = expr.kind;
17 // check for `Some(..)` pattern
18 if let PatKind::TupleStruct(QPath::Resolved(None, pat_path), some_pat, _) = arm.pat.kind;
19 if let Res::Def(_, pat_did) = pat_path.res;
20 if match_def_path(cx, pat_did, &paths::OPTION_SOME);
21 // check for call to `Iterator::next`
22 if let ExprKind::MethodCall(method_name, _, [iter_expr], _) = scrutinee_expr.kind;
23 if method_name.ident.name == sym::next;
24 if is_trait_method(cx, scrutinee_expr, sym::Iterator);
25 if let Some(iter_expr) = try_parse_iter_expr(cx, iter_expr);
26 // get the loop containing the match expression
27 if let Some((_, Node::Expr(loop_expr))) = cx.tcx.hir().parent_iter(expr.hir_id).nth(1);
28 if !uses_iter(cx, &iter_expr, arm.body);
30 (scrutinee_expr, iter_expr, some_pat, loop_expr)
36 let mut applicability = Applicability::MachineApplicable;
37 let loop_var = if let Some(some_pat) = some_pat.first() {
38 if is_refutable(cx, some_pat) {
39 // Refutable patterns don't work with for loops.
42 snippet_with_applicability(cx, some_pat.span, "..", &mut applicability)
47 // If the iterator is a field or the iterator is accessed after the loop is complete it needs to be
48 // borrowed mutably. TODO: If the struct can be partially moved from and the struct isn't used
49 // afterwards a mutable borrow of a field isn't necessary.
50 let ref_mut = if !iter_expr.fields.is_empty() || needs_mutable_borrow(cx, &iter_expr, loop_expr) {
51 if cx.typeck_results().node_type(iter_expr.hir_id).ref_mutability() == Some(Mutability::Mut) {
52 // Reborrow for mutable references. It may not be possible to get a mutable reference here.
61 let iterator = snippet_with_applicability(cx, iter_expr.span, "_", &mut applicability);
64 WHILE_LET_ON_ITERATOR,
65 expr.span.with_hi(scrutinee_expr.span.hi()),
66 "this loop could be written as a `for` loop",
68 format!("for {} in {}{}", loop_var, ref_mut, iterator),
75 /// The span of the whole expression, not just the path and fields stored here.
77 /// The HIR id of the whole expression, not just the path and fields stored here.
79 /// The fields used, in order of child to parent.
81 /// The path being used.
84 /// Parses any expression to find out which field of which variable is used. Will return `None` if
85 /// the expression might have side effects.
86 fn try_parse_iter_expr(cx: &LateContext<'_>, mut e: &Expr<'_>) -> Option<IterExpr> {
88 let hir_id = e.hir_id;
89 let mut fields = Vec::new();
92 ExprKind::Path(ref path) => {
97 path: cx.qpath_res(path, e.hir_id),
100 ExprKind::Field(base, name) => {
101 fields.push(name.name);
104 // Dereferencing a pointer has no side effects and doesn't affect which field is being used.
105 ExprKind::Unary(UnOp::Deref, base) if cx.typeck_results().expr_ty(base).is_ref() => e = base,
107 // Shouldn't have side effects, but there's no way to trace which field is used. So forget which fields have
108 // already been seen.
109 ExprKind::Index(base, idx) if !idx.can_have_side_effects() => {
113 ExprKind::Unary(UnOp::Deref, base) => {
118 // No effect and doesn't affect which field is being used.
119 ExprKind::DropTemps(base) | ExprKind::AddrOf(_, _, base) | ExprKind::Type(base, _) => e = base,
125 fn is_expr_same_field(cx: &LateContext<'_>, mut e: &Expr<'_>, mut fields: &[Symbol], path_res: Res) -> bool {
127 match (&e.kind, fields) {
128 (&ExprKind::Field(base, name), [head_field, tail_fields @ ..]) if name.name == *head_field => {
130 fields = tail_fields;
132 (ExprKind::Path(path), []) => {
133 break cx.qpath_res(path, e.hir_id) == path_res;
135 (&(ExprKind::DropTemps(base) | ExprKind::AddrOf(_, _, base) | ExprKind::Type(base, _)), _) => e = base,
141 /// Checks if the given expression is the same field as, is a child of, or is the parent of the
142 /// given field. Used to check if the expression can be used while the given field is borrowed
143 /// mutably. e.g. if checking for `x.y`, then `x.y`, `x.y.z`, and `x` will all return true, but
144 /// `x.z`, and `y` will return false.
145 fn is_expr_same_child_or_parent_field(cx: &LateContext<'_>, expr: &Expr<'_>, fields: &[Symbol], path_res: Res) -> bool {
147 ExprKind::Field(base, name) => {
148 if let Some((head_field, tail_fields)) = fields.split_first() {
149 if name.name == *head_field && is_expr_same_field(cx, base, tail_fields, path_res) {
152 // Check if the expression is a parent field
153 let mut fields_iter = tail_fields.iter();
154 while let Some(field) = fields_iter.next() {
155 if *field == name.name && is_expr_same_field(cx, base, fields_iter.as_slice(), path_res) {
161 // Check if the expression is a child field.
165 ExprKind::Field(..) if is_expr_same_field(cx, e, fields, path_res) => break true,
166 ExprKind::Field(base, _) | ExprKind::DropTemps(base) | ExprKind::Type(base, _) => e = base,
167 ExprKind::Path(ref path) if fields.is_empty() => {
168 break cx.qpath_res(path, e.hir_id) == path_res;
174 // If the path matches, this is either an exact match, or the expression is a parent of the field.
175 ExprKind::Path(ref path) => cx.qpath_res(path, expr.hir_id) == path_res,
176 ExprKind::DropTemps(base) | ExprKind::Type(base, _) | ExprKind::AddrOf(_, _, base) => {
177 is_expr_same_child_or_parent_field(cx, base, fields, path_res)
183 /// Strips off all field and path expressions. This will return true if a field or path has been
184 /// skipped. Used to skip them after failing to check for equality.
185 fn skip_fields_and_path(expr: &'tcx Expr<'_>) -> (Option<&'tcx Expr<'tcx>>, bool) {
189 ExprKind::Field(base, _) | ExprKind::DropTemps(base) | ExprKind::Type(base, _) => e = base,
190 ExprKind::Path(_) => return (None, true),
194 (Some(e), e.hir_id != expr.hir_id)
197 /// Checks if the given expression uses the iterator.
198 fn uses_iter(cx: &LateContext<'tcx>, iter_expr: &IterExpr, container: &'tcx Expr<'_>) -> bool {
199 struct V<'a, 'b, 'tcx> {
200 cx: &'a LateContext<'tcx>,
201 iter_expr: &'b IterExpr,
204 impl Visitor<'tcx> for V<'_, '_, 'tcx> {
205 type Map = ErasedMap<'tcx>;
206 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
207 NestedVisitorMap::None
210 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
213 } else if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
214 self.uses_iter = true;
215 } else if let (e, true) = skip_fields_and_path(e) {
219 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
220 if is_res_used(self.cx, self.iter_expr.path, id) {
221 self.uses_iter = true;
234 v.visit_expr(container);
238 #[allow(clippy::too_many_lines)]
239 fn needs_mutable_borrow(cx: &LateContext<'tcx>, iter_expr: &IterExpr, loop_expr: &'tcx Expr<'_>) -> bool {
240 struct AfterLoopVisitor<'a, 'b, 'tcx> {
241 cx: &'a LateContext<'tcx>,
242 iter_expr: &'b IterExpr,
247 impl Visitor<'tcx> for AfterLoopVisitor<'_, '_, 'tcx> {
248 type Map = ErasedMap<'tcx>;
249 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
250 NestedVisitorMap::None
253 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
258 if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
259 self.used_iter = true;
260 } else if let (e, true) = skip_fields_and_path(e) {
264 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
265 self.used_iter = is_res_used(self.cx, self.iter_expr.path, id);
269 } else if self.loop_id == e.hir_id {
270 self.after_loop = true;
277 struct NestedLoopVisitor<'a, 'b, 'tcx> {
278 cx: &'a LateContext<'tcx>,
279 iter_expr: &'b IterExpr,
286 impl Visitor<'tcx> for NestedLoopVisitor<'a, 'b, 'tcx> {
287 type Map = ErasedMap<'tcx>;
288 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
289 NestedVisitorMap::None
292 fn visit_local(&mut self, l: &'tcx Local<'_>) {
293 if !self.after_loop {
294 l.pat.each_binding_or_first(&mut |_, id, _, _| {
295 if id == self.local_id {
296 self.found_local = true;
300 if let Some(e) = l.init {
305 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
310 if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
311 self.used_after = true;
312 } else if let (e, true) = skip_fields_and_path(e) {
316 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
317 self.used_after = is_res_used(self.cx, self.iter_expr.path, id);
321 } else if e.hir_id == self.loop_id {
322 self.after_loop = true;
329 if let Some(e) = get_enclosing_loop_or_closure(cx.tcx, loop_expr) {
330 // The iterator expression will be used on the next iteration (for loops), or on the next call (for
331 // closures) unless it is declared within the enclosing expression. TODO: Check for closures
332 // used where an `FnOnce` type is expected.
333 let local_id = match iter_expr.path {
334 Res::Local(id) => id,
337 let mut v = NestedLoopVisitor {
341 loop_id: loop_expr.hir_id,
347 v.used_after || !v.found_local
349 let mut v = AfterLoopVisitor {
352 loop_id: loop_expr.hir_id,
356 v.visit_expr(&cx.tcx.hir().body(cx.enclosing_body.unwrap()).value);