1 use super::WHILE_LET_ON_ITERATOR;
2 use clippy_utils::diagnostics::span_lint_and_sugg;
3 use clippy_utils::source::snippet_with_applicability;
4 use clippy_utils::{get_enclosing_loop, is_refutable, is_trait_method, match_def_path, paths, visitors::is_res_used};
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor};
8 use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, MatchSource, Node, PatKind, QPath, UnOp};
9 use rustc_lint::LateContext;
10 use rustc_span::{symbol::sym, Span, Symbol};
12 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
13 let (scrutinee_expr, iter_expr, some_pat, loop_expr) = if_chain! {
14 if let ExprKind::Match(scrutinee_expr, [arm, _], MatchSource::WhileLetDesugar) = expr.kind;
15 // check for `Some(..)` pattern
16 if let PatKind::TupleStruct(QPath::Resolved(None, pat_path), some_pat, _) = arm.pat.kind;
17 if let Res::Def(_, pat_did) = pat_path.res;
18 if match_def_path(cx, pat_did, &paths::OPTION_SOME);
19 // check for call to `Iterator::next`
20 if let ExprKind::MethodCall(method_name, _, [iter_expr], _) = scrutinee_expr.kind;
21 if method_name.ident.name == sym::next;
22 if is_trait_method(cx, scrutinee_expr, sym::Iterator);
23 if let Some(iter_expr) = try_parse_iter_expr(cx, iter_expr);
24 // get the loop containing the match expression
25 if let Some((_, Node::Expr(loop_expr))) = cx.tcx.hir().parent_iter(expr.hir_id).nth(1);
26 if !uses_iter(cx, &iter_expr, arm.body);
28 (scrutinee_expr, iter_expr, some_pat, loop_expr)
34 let mut applicability = Applicability::MachineApplicable;
35 let loop_var = if let Some(some_pat) = some_pat.first() {
36 if is_refutable(cx, some_pat) {
37 // Refutable patterns don't work with for loops.
40 snippet_with_applicability(cx, some_pat.span, "..", &mut applicability)
45 // If the iterator is a field or the iterator is accessed after the loop is complete it needs to be
46 // borrowed mutably. TODO: If the struct can be partially moved from and the struct isn't used
47 // afterwards a mutable borrow of a field isn't necessary.
48 let ref_mut = if !iter_expr.fields.is_empty() || needs_mutable_borrow(cx, &iter_expr, loop_expr) {
54 let iterator = snippet_with_applicability(cx, iter_expr.span, "_", &mut applicability);
57 WHILE_LET_ON_ITERATOR,
58 expr.span.with_hi(scrutinee_expr.span.hi()),
59 "this loop could be written as a `for` loop",
61 format!("for {} in {}{}", loop_var, ref_mut, iterator),
68 /// The span of the whole expression, not just the path and fields stored here.
70 /// The fields used, in order of child to parent.
72 /// The path being used.
75 /// Parses any expression to find out which field of which variable is used. Will return `None` if
76 /// the expression might have side effects.
77 fn try_parse_iter_expr(cx: &LateContext<'_>, mut e: &Expr<'_>) -> Option<IterExpr> {
79 let mut fields = Vec::new();
82 ExprKind::Path(ref path) => {
86 path: cx.qpath_res(path, e.hir_id),
89 ExprKind::Field(base, name) => {
90 fields.push(name.name);
93 // Dereferencing a pointer has no side effects and doesn't affect which field is being used.
94 ExprKind::Unary(UnOp::Deref, base) if cx.typeck_results().expr_ty(base).is_ref() => e = base,
96 // Shouldn't have side effects, but there's no way to trace which field is used. So forget which fields have
98 ExprKind::Index(base, idx) if !idx.can_have_side_effects() => {
102 ExprKind::Unary(UnOp::Deref, base) => {
107 // No effect and doesn't affect which field is being used.
108 ExprKind::DropTemps(base) | ExprKind::AddrOf(_, _, base) | ExprKind::Type(base, _) => e = base,
114 fn is_expr_same_field(cx: &LateContext<'_>, mut e: &Expr<'_>, mut fields: &[Symbol], path_res: Res) -> bool {
116 match (&e.kind, fields) {
117 (&ExprKind::Field(base, name), [head_field, tail_fields @ ..]) if name.name == *head_field => {
119 fields = tail_fields;
121 (ExprKind::Path(path), []) => {
122 break cx.qpath_res(path, e.hir_id) == path_res;
124 (&(ExprKind::DropTemps(base) | ExprKind::AddrOf(_, _, base) | ExprKind::Type(base, _)), _) => e = base,
130 /// Checks if the given expression is the same field as, is a child of, or is the parent of the
131 /// given field. Used to check if the expression can be used while the given field is borrowed
132 /// mutably. e.g. if checking for `x.y`, then `x.y`, `x.y.z`, and `x` will all return true, but
133 /// `x.z`, and `y` will return false.
134 fn is_expr_same_child_or_parent_field(cx: &LateContext<'_>, expr: &Expr<'_>, fields: &[Symbol], path_res: Res) -> bool {
136 ExprKind::Field(base, name) => {
137 if let Some((head_field, tail_fields)) = fields.split_first() {
138 if name.name == *head_field && is_expr_same_field(cx, base, fields, path_res) {
141 // Check if the expression is a parent field
142 let mut fields_iter = tail_fields.iter();
143 while let Some(field) = fields_iter.next() {
144 if *field == name.name && is_expr_same_field(cx, base, fields_iter.as_slice(), path_res) {
150 // Check if the expression is a child field.
154 ExprKind::Field(..) if is_expr_same_field(cx, e, fields, path_res) => break true,
155 ExprKind::Field(base, _) | ExprKind::DropTemps(base) | ExprKind::Type(base, _) => e = base,
156 ExprKind::Path(ref path) if fields.is_empty() => {
157 break cx.qpath_res(path, e.hir_id) == path_res;
163 // If the path matches, this is either an exact match, or the expression is a parent of the field.
164 ExprKind::Path(ref path) => cx.qpath_res(path, expr.hir_id) == path_res,
165 ExprKind::DropTemps(base) | ExprKind::Type(base, _) | ExprKind::AddrOf(_, _, base) => {
166 is_expr_same_child_or_parent_field(cx, base, fields, path_res)
172 /// Strips off all field and path expressions. This will return true if a field or path has been
173 /// skipped. Used to skip them after failing to check for equality.
174 fn skip_fields_and_path(expr: &'tcx Expr<'_>) -> (Option<&'tcx Expr<'tcx>>, bool) {
178 ExprKind::Field(base, _) | ExprKind::DropTemps(base) | ExprKind::Type(base, _) => e = base,
179 ExprKind::Path(_) => return (None, true),
183 (Some(e), e.hir_id != expr.hir_id)
186 /// Checks if the given expression uses the iterator.
187 fn uses_iter(cx: &LateContext<'tcx>, iter_expr: &IterExpr, container: &'tcx Expr<'_>) -> bool {
188 struct V<'a, 'b, 'tcx> {
189 cx: &'a LateContext<'tcx>,
190 iter_expr: &'b IterExpr,
193 impl Visitor<'tcx> for V<'_, '_, 'tcx> {
194 type Map = ErasedMap<'tcx>;
195 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
196 NestedVisitorMap::None
199 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
202 } else if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
203 self.uses_iter = true;
204 } else if let (e, true) = skip_fields_and_path(e) {
208 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
209 if is_res_used(self.cx, self.iter_expr.path, id) {
210 self.uses_iter = true;
223 v.visit_expr(container);
227 #[allow(clippy::too_many_lines)]
228 fn needs_mutable_borrow(cx: &LateContext<'tcx>, iter_expr: &IterExpr, loop_expr: &'tcx Expr<'_>) -> bool {
229 struct AfterLoopVisitor<'a, 'b, 'tcx> {
230 cx: &'a LateContext<'tcx>,
231 iter_expr: &'b IterExpr,
236 impl Visitor<'tcx> for AfterLoopVisitor<'_, '_, 'tcx> {
237 type Map = ErasedMap<'tcx>;
238 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
239 NestedVisitorMap::None
242 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
247 if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
248 self.used_iter = true;
249 } else if let (e, true) = skip_fields_and_path(e) {
253 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
254 self.used_iter = is_res_used(self.cx, self.iter_expr.path, id);
258 } else if self.loop_id == e.hir_id {
259 self.after_loop = true;
266 struct NestedLoopVisitor<'a, 'b, 'tcx> {
267 cx: &'a LateContext<'tcx>,
268 iter_expr: &'b IterExpr,
275 impl Visitor<'tcx> for NestedLoopVisitor<'a, 'b, 'tcx> {
276 type Map = ErasedMap<'tcx>;
277 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
278 NestedVisitorMap::None
281 fn visit_local(&mut self, l: &'tcx Local<'_>) {
282 if !self.after_loop {
283 l.pat.each_binding_or_first(&mut |_, id, _, _| {
284 if id == self.local_id {
285 self.found_local = true;
289 if let Some(e) = l.init {
294 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
299 if is_expr_same_child_or_parent_field(self.cx, e, &self.iter_expr.fields, self.iter_expr.path) {
300 self.used_after = true;
301 } else if let (e, true) = skip_fields_and_path(e) {
305 } else if let ExprKind::Closure(_, _, id, _, _) = e.kind {
306 self.used_after = is_res_used(self.cx, self.iter_expr.path, id);
310 } else if e.hir_id == self.loop_id {
311 self.after_loop = true;
318 if let Some(e) = get_enclosing_loop(cx.tcx, loop_expr) {
319 // The iterator expression will be used on the next iteration unless it is declared within the outer
321 let local_id = match iter_expr.path {
322 Res::Local(id) => id,
325 let mut v = NestedLoopVisitor {
329 loop_id: loop_expr.hir_id,
335 v.used_after || !v.found_local
337 let mut v = AfterLoopVisitor {
340 loop_id: loop_expr.hir_id,
344 v.visit_expr(&cx.tcx.hir().body(cx.enclosing_body.unwrap()).value);