rust-clippy/clippy_lints/src/needless_borrow.rs
Konrad Borowski 3f62fc3a7e Remove crate:: prefixes from crate paths
This is somewhat misleading, as those are actually external crates,
and don't need a crate:: prefix.
2018-12-29 16:05:49 +01:00

138 lines
5 KiB
Rust

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Checks for needless address of operations (`&`)
//!
//! This lint is **warn** by default
use crate::utils::{in_macro, snippet_opt, span_lint_and_then};
use if_chain::if_chain;
use rustc::hir::{BindingAnnotation, Expr, ExprKind, Item, MutImmutable, Pat, PatKind};
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty;
use rustc::ty::adjustment::{Adjust, Adjustment};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
use syntax::ast::NodeId;
/// **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.
///
/// **Example:**
/// ```rust
/// let x: &i32 = &&&&&&5;
/// ```
///
/// **Known problems:** None.
declare_clippy_lint! {
pub NEEDLESS_BORROW,
nursery,
"taking a reference that is going to be automatically dereferenced"
}
#[derive(Default)]
pub struct NeedlessBorrow {
derived_item: Option<NodeId>,
}
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) || self.derived_item.is_some() {
return;
}
if let ExprKind::AddrOf(MutImmutable, ref inner) = e.node {
if let ty::Ref(..) = 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_with_applicability(
e.span,
"change this to",
snippet,
Applicability::MachineApplicable,
);
}
},
);
}
}
}
}
}
fn check_pat(&mut self, cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat) {
if in_macro(pat.span) || self.derived_item.is_some() {
return;
}
if_chain! {
if let PatKind::Binding(BindingAnnotation::Ref, _, name, _) = pat.node;
if let ty::Ref(_, tam, mutbl) = cx.tables.pat_ty(pat).sty;
if mutbl == MutImmutable;
if let ty::Ref(_, _, mutbl) = tam.sty;
// only lint immutable refs, because borrowed `&mut T` cannot be moved out
if 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_with_applicability(
pat.span,
"change this to",
snippet,
Applicability::MachineApplicable,
);
}
}
)
}
}
}
fn check_item(&mut self, _: &LateContext<'a, 'tcx>, item: &'tcx Item) {
if item.attrs.iter().any(|a| a.check_name("automatically_derived")) {
debug_assert!(self.derived_item.is_none());
self.derived_item = Some(item.id);
}
}
fn check_item_post(&mut self, _: &LateContext<'a, 'tcx>, item: &'tcx Item) {
if let Some(id) = self.derived_item {
if item.id == id {
self.derived_item = None;
}
}
}
}