1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::get_parent_expr;
3 use clippy_utils::source::snippet_with_context;
4 use clippy_utils::ty::{is_type_lang_item, peel_mid_ty_refs};
5 use if_chain::if_chain;
6 use rustc_ast::util::parser::PREC_PREFIX;
7 use rustc_errors::Applicability;
8 use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
9 use rustc_lint::{LateContext, LateLintPass, Lint};
10 use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability};
11 use rustc_middle::ty::subst::GenericArg;
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 declare_clippy_lint! {
16 /// Checks for redundant slicing expressions which use the full range, and
17 /// do not change the type.
19 /// ### Why is this bad?
20 /// It unnecessarily adds complexity to the expression.
22 /// ### Known problems
23 /// If the type being sliced has an implementation of `Index<RangeFull>`
24 /// that actually changes anything then it can't be removed. However, this would be surprising
25 /// to people reading the code and should have a note with it.
29 /// fn get_slice(x: &[u32]) -> &[u32] {
35 /// fn get_slice(x: &[u32]) -> &[u32] {
39 #[clippy::version = "1.51.0"]
40 pub REDUNDANT_SLICING,
42 "redundant slicing of the whole range of a type"
45 declare_clippy_lint! {
47 /// Checks for slicing expressions which are equivalent to dereferencing the
50 /// ### Why is this bad?
51 /// Some people may prefer to dereference rather than slice.
55 /// let vec = vec![1, 2, 3];
56 /// let slice = &vec[..];
60 /// let vec = vec![1, 2, 3];
61 /// let slice = &*vec;
63 #[clippy::version = "1.60.0"]
66 "slicing instead of dereferencing"
69 declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING, DEREF_BY_SLICING]);
71 static REDUNDANT_SLICING_LINT: (&Lint, &str) = (REDUNDANT_SLICING, "redundant slicing of the whole range");
72 static DEREF_BY_SLICING_LINT: (&Lint, &str) = (DEREF_BY_SLICING, "slicing when dereferencing would work");
74 impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
75 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
76 if expr.span.from_expansion() {
80 let ctxt = expr.span.ctxt();
82 if let ExprKind::AddrOf(BorrowKind::Ref, mutability, addressee) = expr.kind;
83 if addressee.span.ctxt() == ctxt;
84 if let ExprKind::Index(indexed, range) = addressee.kind;
85 if is_type_lang_item(cx, cx.typeck_results().expr_ty_adjusted(range), LangItem::RangeFull);
87 let (expr_ty, expr_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(expr));
88 let (indexed_ty, indexed_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(indexed));
89 let parent_expr = get_parent_expr(cx, expr);
90 let needs_parens_for_prefix = parent_expr.map_or(false, |parent| {
91 parent.precedence().order() > PREC_PREFIX
93 let mut app = Applicability::MachineApplicable;
95 let ((lint, msg), help, sugg) = if expr_ty == indexed_ty {
96 if expr_ref_count > indexed_ref_count {
97 // Indexing takes self by reference and can't return a reference to that
98 // reference as it's a local variable. The only way this could happen is if
99 // `self` contains a reference to the `Self` type. If this occurs then the
100 // lint no longer applies as it's essentially a field access, which is not
104 let deref_count = indexed_ref_count - expr_ref_count;
106 let (lint, reborrow_str, help_str) = if mutability == Mutability::Mut {
107 // The slice was used to reborrow the mutable reference.
108 (DEREF_BY_SLICING_LINT, "&mut *", "reborrow the original value instead")
112 kind: ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _),
115 ) || cx.typeck_results().expr_adjustments(expr).first().map_or(false, |a| {
116 matches!(a.kind, Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })))
118 // The slice was used to make a temporary reference.
119 (DEREF_BY_SLICING_LINT, "&*", "reborrow the original value instead")
120 } else if deref_count != 0 {
121 (DEREF_BY_SLICING_LINT, "", "dereference the original value instead")
123 (REDUNDANT_SLICING_LINT, "", "use the original value instead")
126 let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
127 let sugg = if (deref_count != 0 || !reborrow_str.is_empty()) && needs_parens_for_prefix {
128 format!("({}{}{})", reborrow_str, "*".repeat(deref_count), snip)
130 format!("{}{}{}", reborrow_str, "*".repeat(deref_count), snip)
133 (lint, help_str, sugg)
134 } else if let Some(target_id) = cx.tcx.lang_items().deref_target() {
135 if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions(
137 cx.tcx.mk_projection(target_id, cx.tcx.mk_substs([GenericArg::from(indexed_ty)].into_iter())),
139 if deref_ty == expr_ty {
140 let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
141 let sugg = if needs_parens_for_prefix {
142 format!("(&{}{}*{})", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
144 format!("&{}{}*{}", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
146 (DEREF_BY_SLICING_LINT, "dereference the original value instead", sugg)