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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};
use std::iter;
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(iter::once(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,
);
}
}
}
}
|
