100 lines
3.3 KiB
Rust
100 lines
3.3 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 rustc::lint::*;
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use rustc::hir::{BindingAnnotation, Expr, ExprAddrOf, MutImmutable, Pat, PatKind};
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use rustc::ty;
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use rustc::ty::adjustment::{Adjust, Adjustment};
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use utils::{in_macro, snippet_opt, span_lint_and_then};
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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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/// let x: &i32 = &&&&&&5;
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/// ```
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declare_lint! {
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pub NEEDLESS_BORROW,
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Warn,
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"taking a reference that is going to be automatically dereferenced"
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}
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#[derive(Copy, Clone)]
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pub struct NeedlessBorrow;
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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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}
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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) {
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return;
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}
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if let ExprAddrOf(MutImmutable, ref inner) = e.node {
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if let ty::TyRef(..) = 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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..
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}, Adjustment {
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kind: Adjust::Deref(_),
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..
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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(e.span, "change this to", snippet);
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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) {
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return;
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}
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if_let_chain! {[
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let PatKind::Binding(BindingAnnotation::Ref, _, name, _) = pat.node,
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let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
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tam.mutbl == MutImmutable,
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let ty::TyRef(_, ref tam) = tam.ty.sty,
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// only lint immutable refs, because borrowed `&mut T` cannot be moved out
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tam.mutbl == MutImmutable,
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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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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(pat.span, "change this to", snippet);
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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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