1 use clippy_utils::consts::{constant, Constant};
2 use clippy_utils::diagnostics::span_lint_and_then;
3 use clippy_utils::higher::IfLet;
4 use clippy_utils::ty::is_copy;
5 use clippy_utils::{is_expn_of, is_lint_allowed, meets_msrv, msrvs, path_to_local};
6 use if_chain::if_chain;
7 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
8 use rustc_errors::Applicability;
10 use rustc_hir::intravisit::{self, Visitor};
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_middle::hir::nested_filter;
14 use rustc_semver::RustcVersion;
15 use rustc_session::{declare_tool_lint, impl_lint_pass};
16 use rustc_span::{symbol::Ident, Span};
18 declare_clippy_lint! {
20 /// The lint checks for slice bindings in patterns that are only used to
21 /// access individual slice values.
23 /// ### Why is this bad?
24 /// Accessing slice values using indices can lead to panics. Using refutable
25 /// patterns can avoid these. Binding to individual values also improves the
26 /// readability as they can be named.
29 /// This lint currently only checks for immutable access inside `if let`
34 /// let slice: Option<&[u32]> = Some(&[1, 2, 3]);
36 /// if let Some(slice) = slice {
37 /// println!("{}", slice[0]);
42 /// let slice: Option<&[u32]> = Some(&[1, 2, 3]);
44 /// if let Some(&[first, ..]) = slice {
45 /// println!("{}", first);
48 #[clippy::version = "1.59.0"]
49 pub INDEX_REFUTABLE_SLICE,
51 "avoid indexing on slices which could be destructed"
54 #[derive(Copy, Clone)]
55 pub struct IndexRefutableSlice {
56 max_suggested_slice: u64,
57 msrv: Option<RustcVersion>,
60 impl IndexRefutableSlice {
61 pub fn new(max_suggested_slice_pattern_length: u64, msrv: Option<RustcVersion>) -> Self {
63 max_suggested_slice: max_suggested_slice_pattern_length,
69 impl_lint_pass!(IndexRefutableSlice => [INDEX_REFUTABLE_SLICE]);
71 impl<'tcx> LateLintPass<'tcx> for IndexRefutableSlice {
72 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
74 if !expr.span.from_expansion() || is_expn_of(expr.span, "if_chain").is_some();
75 if let Some(IfLet {let_pat, if_then, ..}) = IfLet::hir(cx, expr);
76 if !is_lint_allowed(cx, INDEX_REFUTABLE_SLICE, expr.hir_id);
77 if meets_msrv(self.msrv, msrvs::SLICE_PATTERNS);
79 let found_slices = find_slice_values(cx, let_pat);
80 if !found_slices.is_empty();
81 let filtered_slices = filter_lintable_slices(cx, found_slices, self.max_suggested_slice, if_then);
82 if !filtered_slices.is_empty();
84 for slice in filtered_slices.values() {
85 lint_slice(cx, slice);
91 extract_msrv_attr!(LateContext);
94 fn find_slice_values(cx: &LateContext<'_>, pat: &hir::Pat<'_>) -> FxIndexMap<hir::HirId, SliceLintInformation> {
95 let mut removed_pat: FxHashSet<hir::HirId> = FxHashSet::default();
96 let mut slices: FxIndexMap<hir::HirId, SliceLintInformation> = FxIndexMap::default();
97 pat.walk_always(|pat| {
98 // We'll just ignore mut and ref mut for simplicity sake right now
99 if let hir::PatKind::Binding(
100 hir::BindingAnnotation(by_ref, hir::Mutability::Not),
106 // This block catches bindings with sub patterns. It would be hard to build a correct suggestion
107 // for them and it's likely that the user knows what they are doing in such a case.
108 if removed_pat.contains(&value_hir_id) {
111 if sub_pat.is_some() {
112 removed_pat.insert(value_hir_id);
113 slices.remove(&value_hir_id);
117 let bound_ty = cx.typeck_results().node_type(pat.hir_id);
118 if let ty::Slice(inner_ty) | ty::Array(inner_ty, _) = bound_ty.peel_refs().kind() {
119 // The values need to use the `ref` keyword if they can't be copied.
120 // This will need to be adjusted if the lint want to support mutable access in the future
121 let src_is_ref = bound_ty.is_ref() && by_ref != hir::ByRef::Yes;
122 let needs_ref = !(src_is_ref || is_copy(cx, *inner_ty));
124 let slice_info = slices
126 .or_insert_with(|| SliceLintInformation::new(ident, needs_ref));
127 slice_info.pattern_spans.push(pat.span);
135 fn lint_slice(cx: &LateContext<'_>, slice: &SliceLintInformation) {
136 let used_indices = slice
139 .map(|(index, _)| *index)
140 .collect::<FxHashSet<_>>();
142 let value_name = |index| format!("{}_{}", slice.ident.name, index);
144 if let Some(max_index) = used_indices.iter().max() {
145 let opt_ref = if slice.needs_ref { "ref " } else { "" };
146 let pat_sugg_idents = (0..=*max_index)
148 if used_indices.contains(&index) {
149 format!("{}{}", opt_ref, value_name(index))
154 .collect::<Vec<_>>();
155 let pat_sugg = format!("[{}, ..]", pat_sugg_idents.join(", "));
159 INDEX_REFUTABLE_SLICE,
161 "this binding can be a slice pattern to avoid indexing",
163 diag.multipart_suggestion(
164 "try using a slice pattern here",
168 .map(|span| (*span, pat_sugg.clone()))
170 Applicability::MaybeIncorrect,
173 diag.multipart_suggestion(
174 "and replace the index expressions here",
178 .map(|(index, span)| (*span, value_name(*index)))
180 Applicability::MaybeIncorrect,
183 // The lint message doesn't contain a warning about the removed index expression,
184 // since `filter_lintable_slices` will only return slices where all access indices
185 // are known at compile time. Therefore, they can be removed without side effects.
192 struct SliceLintInformation {
195 pattern_spans: Vec<Span>,
196 index_use: Vec<(u64, Span)>,
199 impl SliceLintInformation {
200 fn new(ident: Ident, needs_ref: bool) -> Self {
204 pattern_spans: Vec::new(),
205 index_use: Vec::new(),
210 fn filter_lintable_slices<'a, 'tcx>(
211 cx: &'a LateContext<'tcx>,
212 slice_lint_info: FxIndexMap<hir::HirId, SliceLintInformation>,
213 max_suggested_slice: u64,
214 scope: &'tcx hir::Expr<'tcx>,
215 ) -> FxIndexMap<hir::HirId, SliceLintInformation> {
216 let mut visitor = SliceIndexLintingVisitor {
222 intravisit::walk_expr(&mut visitor, scope);
224 visitor.slice_lint_info
227 struct SliceIndexLintingVisitor<'a, 'tcx> {
228 cx: &'a LateContext<'tcx>,
229 slice_lint_info: FxIndexMap<hir::HirId, SliceLintInformation>,
230 max_suggested_slice: u64,
233 impl<'a, 'tcx> Visitor<'tcx> for SliceIndexLintingVisitor<'a, 'tcx> {
234 type NestedFilter = nested_filter::OnlyBodies;
236 fn nested_visit_map(&mut self) -> Self::Map {
240 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
241 if let Some(local_id) = path_to_local(expr) {
244 ref mut slice_lint_info,
249 // Check if this is even a local we're interested in
250 if let Some(use_info) = slice_lint_info.get_mut(&local_id);
252 let map = cx.tcx.hir();
254 // Checking for slice indexing
255 let parent_id = map.get_parent_node(expr.hir_id);
256 if let Some(hir::Node::Expr(parent_expr)) = map.find(parent_id);
257 if let hir::ExprKind::Index(_, index_expr) = parent_expr.kind;
258 if let Some((Constant::Int(index_value), _)) = constant(cx, cx.typeck_results(), index_expr);
259 if let Ok(index_value) = index_value.try_into();
260 if index_value < max_suggested_slice;
262 // Make sure that this slice index is read only
263 let maybe_addrof_id = map.get_parent_node(parent_id);
264 if let Some(hir::Node::Expr(maybe_addrof_expr)) = map.find(maybe_addrof_id);
265 if let hir::ExprKind::AddrOf(_kind, hir::Mutability::Not, _inner_expr) = maybe_addrof_expr.kind;
267 use_info.index_use.push((index_value, map.span(parent_expr.hir_id)));
272 // The slice was used for something other than indexing
273 self.slice_lint_info.remove(&local_id);
275 intravisit::walk_expr(self, expr);