mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-22 11:03:16 +00:00
132 lines
4.8 KiB
Rust
132 lines
4.8 KiB
Rust
//! Checks for needless address of operations (`&`)
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//!
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//! This lint is **warn** by default
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use crate::utils::{snippet_opt, span_lint_and_then};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{BindingAnnotation, BorrowKind, Expr, ExprKind, HirId, Item, Mutability, Pat, PatKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_middle::ty::adjustment::{Adjust, Adjustment};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// **What it does:** Checks for address of operations (`&`) that are going to
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/// be dereferenced immediately by the compiler.
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///
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/// **Why is this bad?** Suggests that the receiver of the expression borrows
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/// the expression.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// // Bad
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/// let x: &i32 = &&&&&&5;
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///
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/// // Good
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/// let x: &i32 = &5;
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/// ```
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pub NEEDLESS_BORROW,
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nursery,
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"taking a reference that is going to be automatically dereferenced"
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}
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#[derive(Default)]
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pub struct NeedlessBorrow {
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derived_item: Option<HirId>,
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}
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impl_lint_pass!(NeedlessBorrow => [NEEDLESS_BORROW]);
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impl<'tcx> LateLintPass<'tcx> for NeedlessBorrow {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if e.span.from_expansion() || self.derived_item.is_some() {
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return;
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}
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if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, ref inner) = e.kind {
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if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty(inner).kind() {
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for adj3 in cx.typeck_results().expr_adjustments(e).windows(3) {
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if let [Adjustment {
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kind: Adjust::Deref(_), ..
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}, Adjustment {
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kind: Adjust::Deref(_), ..
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}, Adjustment {
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kind: Adjust::Borrow(_),
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..
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}] = *adj3
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{
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span_lint_and_then(
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cx,
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NEEDLESS_BORROW,
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e.span,
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&format!(
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"this expression borrows a reference (`&{}`) that is immediately dereferenced \
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by the compiler",
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ty
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),
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|diag| {
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if let Some(snippet) = snippet_opt(cx, inner.span) {
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diag.span_suggestion(
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e.span,
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"change this to",
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snippet,
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Applicability::MachineApplicable,
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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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}
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}
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fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
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if pat.span.from_expansion() || self.derived_item.is_some() {
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return;
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}
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if_chain! {
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if let PatKind::Binding(BindingAnnotation::Ref, .., name, _) = pat.kind;
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if let ty::Ref(_, tam, mutbl) = *cx.typeck_results().pat_ty(pat).kind();
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if mutbl == Mutability::Not;
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if let ty::Ref(_, _, mutbl) = *tam.kind();
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// only lint immutable refs, because borrowed `&mut T` cannot be moved out
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if mutbl == Mutability::Not;
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then {
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span_lint_and_then(
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cx,
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NEEDLESS_BORROW,
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pat.span,
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"this pattern creates a reference to a reference",
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|diag| {
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if let Some(snippet) = snippet_opt(cx, name.span) {
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diag.span_suggestion(
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pat.span,
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"change this to",
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snippet,
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Applicability::MachineApplicable,
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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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fn check_item(&mut self, _: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if item.attrs.iter().any(|a| a.has_name(sym::automatically_derived)) {
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debug_assert!(self.derived_item.is_none());
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self.derived_item = Some(item.hir_id);
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}
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}
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fn check_item_post(&mut self, _: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if let Some(id) = self.derived_item {
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if item.hir_id == id {
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self.derived_item = None;
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}
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}
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}
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}
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