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;
+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};
-use rustc_middle::ty::TyS;
+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! {
"redundant slicing of the whole range of a type"
}
-declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING]);
+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 = "1.60.0"]
+ 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 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);
- if TyS::same_type(cx.typeck_results().expr_ty(expr), cx.typeck_results().expr_ty(indexed));
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 snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
- let (reborrow_str, help_str) = if mutability == Mutability::Mut {
- // The slice was used to reborrow the mutable reference.
- ("&mut *", "reborrow the original value instead")
- } else if matches!(
- get_parent_expr(cx, expr),
- Some(Expr {
- kind: ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, _),
- ..
- })
- ) {
- // The slice was used to make a temporary reference.
- ("&*", "reborrow the original value instead")
+ 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, "*".repeat(deref_count), snip)
+ } else {
+ format!("{}{}{}", reborrow_str, "*".repeat(deref_count), snip)
+ };
+
+ (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)].into_iter())),
+ ) {
+ 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!("(&{}{}*{})", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
+ } else {
+ format!("&{}{}*{}", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
+ };
+ (DEREF_BY_SLICING_LINT, "dereference the original value instead", sugg)
+ } else {
+ return;
+ }
+ } else {
+ return;
+ }
} else {
- ("", "use the original value instead")
+ return;
};
span_lint_and_sugg(
cx,
- REDUNDANT_SLICING,
+ lint,
expr.span,
- "redundant slicing of the whole range",
- help_str,
- format!("{}{}", reborrow_str, snip),
+ msg,
+ help,
+ sugg,
app,
);
}
projects / rust.git / blobdiff