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Improve redundant_slicing lint

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* Lint when slicing triggers auto-deref
* Lint when slicing returns the same type as dereferencing
This commit is contained in:
Jason Newcomb
2022-01-03 15:25:00 -05:00
parent e2dc8ca080
commit faeeef3b9c
4 changed files with 134 additions and 31 deletions
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67
clippy_lints/src/redundant_slicing.rs
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@@ -1,11 +1,12 @@
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_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::subst::GenericArg;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
@@ -53,25 +54,55 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
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 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 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 (help, sugg) = if expr_ty == indexed_ty {
if expr_ref_count > indexed_ref_count {
return;
}
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")
} else if expr_ref_count != indexed_ref_count {
("", "dereference the original value instead")
} else {
("", "use the original value instead")
};
let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
(help_str, format!("{}{}{}", reborrow_str, "*".repeat(indexed_ref_count - expr_ref_count), snip))
} 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;
(
"dereference the original value instead",
format!("&{}{}*{}", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip),
)
} else {
return;
}
} else {
return;
}
} else {
("", "use the original value instead")
return;
};
span_lint_and_sugg(
@@ -79,8 +110,8 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
REDUNDANT_SLICING,
expr.span,
"redundant slicing of the whole range",
help_str,
format!("{}{}", reborrow_str, snip),
help,
sugg,
app,
);
}