rust-clippy/clippy_lints/src/borrow_deref_ref.rs

116 lines
4.3 KiB
Rust

use crate::reference::DEREF_ADDROF;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::implements_trait;
use clippy_utils::{get_parent_expr, is_lint_allowed};
use rustc_errors::Applicability;
use rustc_hir::{ExprKind, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::mir::Mutability;
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for `&*(&T)`.
///
/// ### Why is this bad?
/// Dereferencing and then borrowing a reference value has no effect in most cases.
///
/// ### Known problems
/// False negative on such code:
/// ```
/// let x = &12;
/// let addr_x = &x as *const _ as usize;
/// let addr_y = &&*x as *const _ as usize; // assert ok now, and lint triggered.
/// // But if we fix it, assert will fail.
/// assert_ne!(addr_x, addr_y);
/// ```
///
/// ### Example
/// ```rust
/// let s = &String::new();
///
/// let a: &String = &* s;
/// ```
///
/// Use instead:
/// ```rust
/// # let s = &String::new();
/// let a: &String = s;
/// ```
#[clippy::version = "1.63.0"]
pub BORROW_DEREF_REF,
complexity,
"deref on an immutable reference returns the same type as itself"
}
declare_lint_pass!(BorrowDerefRef => [BORROW_DEREF_REF]);
impl LateLintPass<'_> for BorrowDerefRef {
fn check_expr(&mut self, cx: &LateContext<'_>, e: &rustc_hir::Expr<'_>) {
if_chain! {
if !e.span.from_expansion();
if let ExprKind::AddrOf(_, Mutability::Not, addrof_target) = e.kind;
if !addrof_target.span.from_expansion();
if let ExprKind::Unary(UnOp::Deref, deref_target) = addrof_target.kind;
if !deref_target.span.from_expansion();
if !matches!(deref_target.kind, ExprKind::Unary(UnOp::Deref, ..) );
let ref_ty = cx.typeck_results().expr_ty(deref_target);
if let ty::Ref(_, inner_ty, Mutability::Not) = ref_ty.kind();
then{
if let Some(parent_expr) = get_parent_expr(cx, e){
if matches!(parent_expr.kind, ExprKind::Unary(UnOp::Deref, ..)) &&
!is_lint_allowed(cx, DEREF_ADDROF, parent_expr.hir_id) {
return;
}
// modification to `&mut &*x` is different from `&mut x`
if matches!(deref_target.kind, ExprKind::Path(..)
| ExprKind::Field(..)
| ExprKind::Index(..)
| ExprKind::Unary(UnOp::Deref, ..))
&& matches!(parent_expr.kind, ExprKind::AddrOf(_, Mutability::Mut, _)) {
return;
}
}
span_lint_and_then(
cx,
BORROW_DEREF_REF,
e.span,
"deref on an immutable reference",
|diag| {
diag.span_suggestion(
e.span,
"if you would like to reborrow, try removing `&*`",
snippet_opt(cx, deref_target.span).unwrap(),
Applicability::MachineApplicable
);
// has deref trait -> give 2 help
// doesn't have deref trait -> give 1 help
if let Some(deref_trait_id) = cx.tcx.lang_items().deref_trait(){
if !implements_trait(cx, *inner_ty, deref_trait_id, &[]) {
return;
}
}
diag.span_suggestion(
e.span,
"if you would like to deref, try using `&**`",
format!(
"&**{}",
&snippet_opt(cx, deref_target.span).unwrap(),
),
Applicability::MaybeIncorrect
);
}
);
}
}
}
}