mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-22 19:13:29 +00:00
169 lines
7.2 KiB
Rust
169 lines
7.2 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::get_parent_expr;
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use clippy_utils::source::snippet_with_context;
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use clippy_utils::ty::{is_type_lang_item, peel_mid_ty_refs};
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use if_chain::if_chain;
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use rustc_ast::util::parser::PREC_PREFIX;
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use rustc_errors::Applicability;
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use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
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use rustc_lint::{LateContext, LateLintPass, Lint};
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use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability};
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use rustc_middle::ty::subst::GenericArg;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for redundant slicing expressions which use the full range, and
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/// do not change the type.
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///
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/// ### Why is this bad?
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/// It unnecessarily adds complexity to the expression.
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///
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/// ### Known problems
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/// If the type being sliced has an implementation of `Index<RangeFull>`
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/// that actually changes anything then it can't be removed. However, this would be surprising
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/// to people reading the code and should have a note with it.
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///
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/// ### Example
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/// ```ignore
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/// fn get_slice(x: &[u32]) -> &[u32] {
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/// &x[..]
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/// }
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/// ```
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/// Use instead:
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/// ```ignore
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/// fn get_slice(x: &[u32]) -> &[u32] {
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/// x
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/// }
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/// ```
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#[clippy::version = "1.51.0"]
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pub REDUNDANT_SLICING,
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complexity,
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"redundant slicing of the whole range of a type"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for slicing expressions which are equivalent to dereferencing the
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/// value.
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///
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/// ### Why is this bad?
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/// Some people may prefer to dereference rather than slice.
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///
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/// ### Example
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/// ```rust
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/// let vec = vec![1, 2, 3];
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/// let slice = &vec[..];
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/// ```
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/// Use instead:
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/// ```rust
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/// let vec = vec![1, 2, 3];
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/// let slice = &*vec;
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/// ```
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#[clippy::version = "1.61.0"]
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pub DEREF_BY_SLICING,
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restriction,
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"slicing instead of dereferencing"
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}
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declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING, DEREF_BY_SLICING]);
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static REDUNDANT_SLICING_LINT: (&Lint, &str) = (REDUNDANT_SLICING, "redundant slicing of the whole range");
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static DEREF_BY_SLICING_LINT: (&Lint, &str) = (DEREF_BY_SLICING, "slicing when dereferencing would work");
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impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if expr.span.from_expansion() {
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return;
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}
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let ctxt = expr.span.ctxt();
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if_chain! {
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if let ExprKind::AddrOf(BorrowKind::Ref, mutability, addressee) = expr.kind;
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if addressee.span.ctxt() == ctxt;
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if let ExprKind::Index(indexed, range) = addressee.kind;
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if is_type_lang_item(cx, cx.typeck_results().expr_ty_adjusted(range), LangItem::RangeFull);
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then {
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let (expr_ty, expr_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(expr));
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let (indexed_ty, indexed_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(indexed));
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let parent_expr = get_parent_expr(cx, expr);
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let needs_parens_for_prefix = parent_expr.map_or(false, |parent| {
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parent.precedence().order() > PREC_PREFIX
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});
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let mut app = Applicability::MachineApplicable;
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let ((lint, msg), help, sugg) = if expr_ty == indexed_ty {
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if expr_ref_count > indexed_ref_count {
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// Indexing takes self by reference and can't return a reference to that
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// reference as it's a local variable. The only way this could happen is if
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// `self` contains a reference to the `Self` type. If this occurs then the
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// lint no longer applies as it's essentially a field access, which is not
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// redundant.
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return;
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}
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let deref_count = indexed_ref_count - expr_ref_count;
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let (lint, reborrow_str, help_str) = if mutability == Mutability::Mut {
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// The slice was used to reborrow the mutable reference.
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(DEREF_BY_SLICING_LINT, "&mut *", "reborrow the original value instead")
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} else if matches!(
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parent_expr,
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Some(Expr {
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kind: ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _),
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..
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})
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) || cx.typeck_results().expr_adjustments(expr).first().map_or(false, |a| {
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matches!(a.kind, Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })))
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}) {
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// The slice was used to make a temporary reference.
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(DEREF_BY_SLICING_LINT, "&*", "reborrow the original value instead")
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} else if deref_count != 0 {
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(DEREF_BY_SLICING_LINT, "", "dereference the original value instead")
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} else {
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(REDUNDANT_SLICING_LINT, "", "use the original value instead")
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};
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let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
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let sugg = if (deref_count != 0 || !reborrow_str.is_empty()) && needs_parens_for_prefix {
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format!("({}{}{})", reborrow_str, "*".repeat(deref_count), snip)
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} else {
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format!("{}{}{}", reborrow_str, "*".repeat(deref_count), snip)
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};
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(lint, help_str, sugg)
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} else if let Some(target_id) = cx.tcx.lang_items().deref_target() {
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if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions(
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cx.param_env,
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cx.tcx.mk_projection(target_id, cx.tcx.mk_substs([GenericArg::from(indexed_ty)].into_iter())),
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) {
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if deref_ty == expr_ty {
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let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
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let sugg = if needs_parens_for_prefix {
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format!("(&{}{}*{})", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
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} else {
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format!("&{}{}*{}", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
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};
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(DEREF_BY_SLICING_LINT, "dereference the original value instead", sugg)
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} else {
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return;
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}
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} else {
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return;
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}
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} else {
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return;
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};
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span_lint_and_sugg(
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cx,
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lint,
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expr.span,
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msg,
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help,
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sugg,
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app,
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);
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}
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}
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}
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}
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