rust-clippy/clippy_lints/src/needless_borrowed_ref.rs

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//! Checks for useless borrowed references.
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//!
//! This lint is **warn** by default
use rustc::lint::*;
use rustc::hir::{MutImmutable, Pat, PatKind, BindingAnnotation};
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use rustc::ty;
use utils::{span_lint, in_macro};
/// **What it does:** Checks for useless borrowed references.
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///
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/// **Why is this bad?** It is completely useless and make the code look more
/// complex than it
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/// actually is.
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///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let mut v = Vec::<String>::new();
/// let _ = v.iter_mut().filter(|&ref a| a.is_empty());
/// ```
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/// This clojure takes a reference on something that has been matched as a
/// reference and
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/// de-referenced.
/// As such, it could just be |a| a.is_empty()
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declare_lint! {
pub NEEDLESS_BORROWED_REFERENCE,
Warn,
"taking a needless borrowed reference"
}
#[derive(Copy, Clone)]
pub struct NeedlessBorrowedRef;
impl LintPass for NeedlessBorrowedRef {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_BORROWED_REFERENCE)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrowedRef {
fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
if in_macro(pat.span) {
// OK, simple enough, lints doesn't check in macro.
return;
}
if_let_chain! {[
// Pat is a pattern whose node
// is a binding which "involves" a immutable reference...
let PatKind::Binding(BindingAnnotation::Ref, ..) = pat.node,
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// Pattern's type is a reference. Get the type and mutability of referenced value (tam: TypeAndMut).
let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty,
// This is an immutable reference.
tam.mutbl == MutImmutable,
], {
span_lint(cx, NEEDLESS_BORROWED_REFERENCE, pat.span, "this pattern takes a reference on something that is being de-referenced")
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}}
}
}