| use clippy_utils::diagnostics::span_lint_and_sugg; |
| use clippy_utils::get_parent_expr; |
| use clippy_utils::source::snippet_with_context; |
| use clippy_utils::ty::{is_type_lang_item, peel_mid_ty_refs}; |
| use if_chain::if_chain; |
| use rustc_ast::util::parser::PREC_PREFIX; |
| use rustc_errors::Applicability; |
| use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability}; |
| use rustc_lint::{LateContext, LateLintPass, Lint}; |
| use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability}; |
| use rustc_middle::ty::subst::GenericArg; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for redundant slicing expressions which use the full range, and |
| /// do not change the type. |
| /// |
| /// ### Why is this bad? |
| /// It unnecessarily adds complexity to the expression. |
| /// |
| /// ### Known problems |
| /// If the type being sliced has an implementation of `Index<RangeFull>` |
| /// that actually changes anything then it can't be removed. However, this would be surprising |
| /// to people reading the code and should have a note with it. |
| /// |
| /// ### Example |
| /// ```ignore |
| /// fn get_slice(x: &[u32]) -> &[u32] { |
| /// &x[..] |
| /// } |
| /// ``` |
| /// Use instead: |
| /// ```ignore |
| /// fn get_slice(x: &[u32]) -> &[u32] { |
| /// x |
| /// } |
| /// ``` |
| #[clippy::version = "1.51.0"] |
| pub REDUNDANT_SLICING, |
| complexity, |
| "redundant slicing of the whole range of a type" |
| } |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks for slicing expressions which are equivalent to dereferencing the |
| /// value. |
| /// |
| /// ### Why is this bad? |
| /// Some people may prefer to dereference rather than slice. |
| /// |
| /// ### Example |
| /// ```rust |
| /// let vec = vec![1, 2, 3]; |
| /// let slice = &vec[..]; |
| /// ``` |
| /// Use instead: |
| /// ```rust |
| /// let vec = vec![1, 2, 3]; |
| /// let slice = &*vec; |
| /// ``` |
| #[clippy::version = "1.61.0"] |
| pub DEREF_BY_SLICING, |
| restriction, |
| "slicing instead of dereferencing" |
| } |
| |
| declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING, DEREF_BY_SLICING]); |
| |
| static REDUNDANT_SLICING_LINT: (&Lint, &str) = (REDUNDANT_SLICING, "redundant slicing of the whole range"); |
| static DEREF_BY_SLICING_LINT: (&Lint, &str) = (DEREF_BY_SLICING, "slicing when dereferencing would work"); |
| |
| impl<'tcx> LateLintPass<'tcx> for RedundantSlicing { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if expr.span.from_expansion() { |
| return; |
| } |
| |
| let ctxt = expr.span.ctxt(); |
| if_chain! { |
| if let ExprKind::AddrOf(BorrowKind::Ref, mutability, addressee) = expr.kind; |
| if addressee.span.ctxt() == ctxt; |
| if let ExprKind::Index(indexed, range) = addressee.kind; |
| if is_type_lang_item(cx, cx.typeck_results().expr_ty_adjusted(range), LangItem::RangeFull); |
| then { |
| let (expr_ty, expr_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(expr)); |
| let (indexed_ty, indexed_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(indexed)); |
| let parent_expr = get_parent_expr(cx, expr); |
| let needs_parens_for_prefix = parent_expr.map_or(false, |parent| { |
| parent.precedence().order() > PREC_PREFIX |
| }); |
| let mut app = Applicability::MachineApplicable; |
| |
| let ((lint, msg), help, sugg) = if expr_ty == indexed_ty { |
| if expr_ref_count > indexed_ref_count { |
| // Indexing takes self by reference and can't return a reference to that |
| // reference as it's a local variable. The only way this could happen is if |
| // `self` contains a reference to the `Self` type. If this occurs then the |
| // lint no longer applies as it's essentially a field access, which is not |
| // redundant. |
| return; |
| } |
| let deref_count = indexed_ref_count - expr_ref_count; |
| |
| let (lint, reborrow_str, help_str) = if mutability == Mutability::Mut { |
| // The slice was used to reborrow the mutable reference. |
| (DEREF_BY_SLICING_LINT, "&mut *", "reborrow the original value instead") |
| } else if matches!( |
| parent_expr, |
| Some(Expr { |
| kind: ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _), |
| .. |
| }) |
| ) || cx.typeck_results().expr_adjustments(expr).first().map_or(false, |a| { |
| matches!(a.kind, Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. }))) |
| }) { |
| // The slice was used to make a temporary reference. |
| (DEREF_BY_SLICING_LINT, "&*", "reborrow the original value instead") |
| } else if deref_count != 0 { |
| (DEREF_BY_SLICING_LINT, "", "dereference the original value instead") |
| } else { |
| (REDUNDANT_SLICING_LINT, "", "use the original value instead") |
| }; |
| |
| let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0; |
| let sugg = if (deref_count != 0 || !reborrow_str.is_empty()) && needs_parens_for_prefix { |
| format!("({reborrow_str}{}{snip})", "*".repeat(deref_count)) |
| } else { |
| format!("{reborrow_str}{}{snip}", "*".repeat(deref_count)) |
| }; |
| |
| (lint, help_str, sugg) |
| } else if let Some(target_id) = cx.tcx.lang_items().deref_target() { |
| if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions( |
| cx.param_env, |
| cx.tcx.mk_projection(target_id, cx.tcx.mk_substs(&[GenericArg::from(indexed_ty)])), |
| ) { |
| if deref_ty == expr_ty { |
| let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0; |
| let sugg = if needs_parens_for_prefix { |
| format!("(&{}{}*{snip})", mutability.prefix_str(), "*".repeat(indexed_ref_count)) |
| } else { |
| format!("&{}{}*{snip}", mutability.prefix_str(), "*".repeat(indexed_ref_count)) |
| }; |
| (DEREF_BY_SLICING_LINT, "dereference the original value instead", sugg) |
| } else { |
| return; |
| } |
| } else { |
| return; |
| } |
| } else { |
| return; |
| }; |
| |
| span_lint_and_sugg( |
| cx, |
| lint, |
| expr.span, |
| msg, |
| help, |
| sugg, |
| app, |
| ); |
| } |
| } |
| } |
| } |