119 lines
4.3 KiB
Rust
119 lines
4.3 KiB
Rust
use crate::reference::DEREF_ADDROF;
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet_opt;
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use clippy_utils::ty::implements_trait;
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use clippy_utils::{get_parent_expr, is_lint_allowed};
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use rustc_errors::Applicability;
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use rustc_hir::{ExprKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::mir::Mutability;
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for `&*(&T)`.
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///
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/// ### Why is this bad?
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/// Dereferencing and then borrowing a reference value has no effect in most cases.
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///
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/// ### Known problems
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/// false negative on such code:
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/// ```
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/// let x = &12;
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/// let addr_x = &x as *const _ as usize;
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/// let addr_y = &&*x as *const _ as usize; // assert ok now, and lint triggerd.
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/// // But if we fix it, assert will fail.
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/// assert_ne!(addr_x, addr_y);
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/// ```
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///
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/// ### Example
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/// ```rust
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/// let s = &String::new();
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///
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/// // Bad
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/// let a: &String = &* s;
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/// foo(&*s);
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///
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/// // Good
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/// let a: &String = s;
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/// foo(&**s);
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///
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/// fn foo(_: &str){ }
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/// ```
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#[clippy::version = "1.59.0"]
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pub BORROW_DEREF_REF,
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complexity,
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"deref on an immutable reference returns the same type as itself"
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}
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declare_lint_pass!(BorrowDerefRef => [BORROW_DEREF_REF]);
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impl LateLintPass<'_> for BorrowDerefRef {
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fn check_expr(&mut self, cx: &LateContext<'_>, e: &rustc_hir::Expr<'_>) {
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if_chain! {
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if !e.span.from_expansion();
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if let ExprKind::AddrOf(_, Mutability::Not, addrof_target) = e.kind;
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if !addrof_target.span.from_expansion();
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if let ExprKind::Unary(UnOp::Deref, deref_target) = addrof_target.kind;
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if !deref_target.span.from_expansion();
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if !matches!(deref_target.kind, ExprKind::Unary(UnOp::Deref, ..) );
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let ref_ty = cx.typeck_results().expr_ty(deref_target);
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if let ty::Ref(_, inner_ty, Mutability::Not) = ref_ty.kind();
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then{
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if let Some(parent_expr) = get_parent_expr(cx, e){
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if matches!(parent_expr.kind, ExprKind::Unary(UnOp::Deref, ..)) &&
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!is_lint_allowed(cx, DEREF_ADDROF, parent_expr.hir_id) {
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return;
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}
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// modification to `&mut &*x` is different from `&mut x`
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if matches!(deref_target.kind, ExprKind::Path(..)
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| ExprKind::Field(..)
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| ExprKind::Index(..)
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| ExprKind::Unary(UnOp::Deref, ..))
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&& matches!(parent_expr.kind, ExprKind::AddrOf(_, Mutability::Mut, _)) {
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return;
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}
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}
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span_lint_and_then(
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cx,
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BORROW_DEREF_REF,
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e.span,
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"deref on an immutable reference",
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|diag| {
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diag.span_suggestion(
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e.span,
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"if you would like to reborrow, try removing `&*`",
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snippet_opt(cx, deref_target.span).unwrap(),
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Applicability::MachineApplicable
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);
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// has deref trait -> give 2 help
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// doesn't have deref trait -> give 1 help
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if let Some(deref_trait_id) = cx.tcx.lang_items().deref_trait(){
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if !implements_trait(cx, *inner_ty, deref_trait_id, &[]) {
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return;
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}
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}
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diag.span_suggestion(
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e.span,
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"if you would like to deref, try using `&**`",
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format!(
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"&**{}",
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&snippet_opt(cx, deref_target.span).unwrap(),
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),
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Applicability::MaybeIncorrect
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);
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}
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);
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}
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}
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}
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}
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