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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet_with_applicability;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BindingAnnotation, Mutability, Node, Pat, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for bindings that destructure a reference and borrow the inner
/// value with `&ref`.
///
/// ### Why is this bad?
/// This pattern has no effect in almost all cases.
///
/// ### Known problems
/// In some cases, `&ref` is needed to avoid a lifetime mismatch error.
/// Example:
/// ```rust
/// fn foo(a: &Option<String>, b: &Option<String>) {
/// match (a, b) {
/// (None, &ref c) | (&ref c, None) => (),
/// (&Some(ref c), _) => (),
/// };
/// }
/// ```
///
/// ### Example
/// ```rust
/// let mut v = Vec::<String>::new();
/// # #[allow(unused)]
/// v.iter_mut().filter(|&ref a| a.is_empty());
/// ```
///
/// Use instead:
/// ```rust
/// let mut v = Vec::<String>::new();
/// # #[allow(unused)]
/// v.iter_mut().filter(|a| a.is_empty());
/// ```
#[clippy::version = "pre 1.29.0"]
pub NEEDLESS_BORROWED_REFERENCE,
complexity,
"destructuring a reference and borrowing the inner value"
}
declare_lint_pass!(NeedlessBorrowedRef => [NEEDLESS_BORROWED_REFERENCE]);
impl<'tcx> LateLintPass<'tcx> for NeedlessBorrowedRef {
fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
if pat.span.from_expansion() {
// OK, simple enough, lints doesn't check in macro.
return;
}
if_chain! {
// Only lint immutable refs, because `&mut ref T` may be useful.
if let PatKind::Ref(sub_pat, Mutability::Not) = pat.kind;
// Check sub_pat got a `ref` keyword (excluding `ref mut`).
if let PatKind::Binding(BindingAnnotation::REF, .., spanned_name, _) = sub_pat.kind;
let parent_id = cx.tcx.hir().get_parent_node(pat.hir_id);
if let Some(parent_node) = cx.tcx.hir().find(parent_id);
then {
// do not recurse within patterns, as they may have other references
// XXXManishearth we can relax this constraint if we only check patterns
// with a single ref pattern inside them
if let Node::Pat(_) = parent_node {
return;
}
let mut applicability = Applicability::MachineApplicable;
span_lint_and_then(cx, NEEDLESS_BORROWED_REFERENCE, pat.span,
"this pattern takes a reference on something that is being de-referenced",
|diag| {
let hint = snippet_with_applicability(cx, spanned_name.span, "..", &mut applicability).into_owned();
diag.span_suggestion(
pat.span,
"try removing the `&ref` part and just keep",
hint,
applicability,
);
});
}
}
}
}
|
