rust-clippy/clippy_lints/src/redundant_slicing.rs

67 lines
2.3 KiB
Rust

use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, LangItem};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::{lint::in_external_macro, ty::TyS};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::{is_type_lang_item, snippet_with_applicability, span_lint_and_sugg};
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
/// }
/// ```
pub REDUNDANT_SLICING,
complexity,
"redundant slicing of the whole range of a type"
}
declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING]);
impl LateLintPass<'_> for RedundantSlicing {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if in_external_macro(cx.sess(), expr.span) {
return;
}
if_chain! {
if let ExprKind::AddrOf(_, _, addressee) = expr.kind;
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 mut app = Applicability::MachineApplicable;
let hint = snippet_with_applicability(cx, indexed.span, "..", &mut app).into_owned();
span_lint_and_sugg(
cx,
REDUNDANT_SLICING,
expr.span,
"redundant slicing of the whole range",
"use the original slice instead",
hint,
app,
);
}
}
}
}