rust/clippy_lints/src/needless_borrow.rs
2018-04-08 11:13:46 +02:00

101 lines
3.4 KiB
Rust

//! Checks for needless address of operations (`&`)
//!
//! This lint is **warn** by default
use rustc::lint::*;
use rustc::hir::{BindingAnnotation, Expr, ExprAddrOf, MutImmutable, Pat, PatKind};
use rustc::ty;
use rustc::ty::adjustment::{Adjust, Adjustment};
use utils::{in_macro, snippet_opt, span_lint_and_then};
/// **What it does:** Checks for address of operations (`&`) that are going to
/// be dereferenced immediately by the compiler.
///
/// **Why is this bad?** Suggests that the receiver of the expression borrows
/// the expression.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x: &i32 = &&&&&&5;
/// ```
declare_clippy_lint! {
pub NEEDLESS_BORROW,
nursery,
"taking a reference that is going to be automatically dereferenced"
}
#[derive(Copy, Clone)]
pub struct NeedlessBorrow;
impl LintPass for NeedlessBorrow {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_BORROW)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBorrow {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
return;
}
if let ExprAddrOf(MutImmutable, ref inner) = e.node {
if let ty::TyRef(..) = cx.tables.expr_ty(inner).sty {
for adj3 in cx.tables.expr_adjustments(e).windows(3) {
if let [Adjustment {
kind: Adjust::Deref(_),
..
}, Adjustment {
kind: Adjust::Deref(_),
..
}, Adjustment {
kind: Adjust::Borrow(_),
..
}] = *adj3
{
span_lint_and_then(
cx,
NEEDLESS_BORROW,
e.span,
"this expression borrows a reference that is immediately dereferenced \
by the compiler",
|db| {
if let Some(snippet) = snippet_opt(cx, inner.span) {
db.span_suggestion(e.span, "change this to", snippet);
}
},
);
}
}
}
}
}
fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
if in_macro(pat.span) {
return;
}
if_chain! {
if let PatKind::Binding(BindingAnnotation::Ref, _, name, _) = pat.node;
if let ty::TyRef(_, ref tam) = cx.tables.pat_ty(pat).sty;
if tam.mutbl == MutImmutable;
if let ty::TyRef(_, ref tam) = tam.ty.sty;
// only lint immutable refs, because borrowed `&mut T` cannot be moved out
if tam.mutbl == MutImmutable;
then {
span_lint_and_then(
cx,
NEEDLESS_BORROW,
pat.span,
"this pattern creates a reference to a reference",
|db| {
if let Some(snippet) = snippet_opt(cx, name.span) {
db.span_suggestion(pat.span, "change this to", snippet);
}
}
)
}
}
}
}