133 lines
4.6 KiB
Rust
133 lines
4.6 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::{in_macro, snippet_opt, span_lint_and_then};
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use if_chain::if_chain;
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use rustc::hir::{BindingAnnotation, Expr, ExprKind, HirId, Item, MutImmutable, Pat, PatKind};
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::ty;
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use rustc::ty::adjustment::{Adjust, Adjustment};
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use rustc::{declare_tool_lint, lint_array};
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use rustc_errors::Applicability;
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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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/// **Example:**
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/// ```rust
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/// let x: &i32 = &&&&&&5;
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/// ```
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///
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/// **Known problems:** None.
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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 LintPass for NeedlessBorrow {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_BORROW)
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}
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fn name(&self) -> &'static str {
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"NeedlessBorrow"
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrow {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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if in_macro(e.span) || self.derived_item.is_some() {
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return;
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}
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if let ExprKind::AddrOf(MutImmutable, ref inner) = e.node {
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if let ty::Ref(..) = cx.tables.expr_ty(inner).sty {
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for adj3 in cx.tables.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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"this expression borrows a reference that is immediately dereferenced \
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by the compiler",
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|db| {
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if let Some(snippet) = snippet_opt(cx, inner.span) {
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db.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<'a, 'tcx>, pat: &'tcx Pat) {
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if in_macro(pat.span) || 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.node;
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if let ty::Ref(_, tam, mutbl) = cx.tables.pat_ty(pat).sty;
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if mutbl == MutImmutable;
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if let ty::Ref(_, _, mutbl) = tam.sty;
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// only lint immutable refs, because borrowed `&mut T` cannot be moved out
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if mutbl == MutImmutable;
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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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|db| {
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if let Some(snippet) = snippet_opt(cx, name.span) {
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db.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<'a, 'tcx>, item: &'tcx Item) {
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if item.attrs.iter().any(|a| a.check_name("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<'a, '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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