rust/clippy_lints/src/mut_mut.rs
2018-03-28 15:24:26 +02:00

123 lines
3.4 KiB
Rust

use rustc::hir;
use rustc::hir::intravisit;
use rustc::lint::*;
use rustc::ty;
use utils::{higher, in_external_macro, span_lint};
/// **What it does:** Checks for instances of `mut mut` references.
///
/// **Why is this bad?** Multiple `mut`s don't add anything meaningful to the
/// source. This is either a copy'n'paste error, or it shows a fundamental
/// misunderstanding of references.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x = &mut &mut y;
/// ```
declare_clippy_lint! {
pub MUT_MUT,
pedantic,
"usage of double-mut refs, e.g. `&mut &mut ...`"
}
#[derive(Copy, Clone)]
pub struct MutMut;
impl LintPass for MutMut {
fn get_lints(&self) -> LintArray {
lint_array!(MUT_MUT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutMut {
fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block) {
intravisit::walk_block(&mut MutVisitor { cx }, block);
}
fn check_ty(&mut self, cx: &LateContext<'a, 'tcx>, ty: &'tcx hir::Ty) {
use rustc::hir::intravisit::Visitor;
MutVisitor { cx }.visit_ty(ty);
}
}
pub struct MutVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
}
impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
if in_external_macro(self.cx, expr.span) {
return;
}
if let Some((_, arg, body)) = higher::for_loop(expr) {
// A `for` loop lowers to:
// ```rust
// match ::std::iter::Iterator::next(&mut iter) {
// // ^^^^
// ```
// Let's ignore the generated code.
intravisit::walk_expr(self, arg);
intravisit::walk_expr(self, body);
} else if let hir::ExprAddrOf(hir::MutMutable, ref e) = expr.node {
if let hir::ExprAddrOf(hir::MutMutable, _) = e.node {
span_lint(
self.cx,
MUT_MUT,
expr.span,
"generally you want to avoid `&mut &mut _` if possible",
);
} else if let ty::TyRef(
_,
ty::TypeAndMut {
mutbl: hir::MutMutable,
..
},
) = self.cx.tables.expr_ty(e).sty
{
span_lint(
self.cx,
MUT_MUT,
expr.span,
"this expression mutably borrows a mutable reference. Consider reborrowing",
);
}
}
}
fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
if let hir::TyRptr(
_,
hir::MutTy {
ty: ref pty,
mutbl: hir::MutMutable,
},
) = ty.node
{
if let hir::TyRptr(
_,
hir::MutTy {
mutbl: hir::MutMutable,
..
},
) = pty.node
{
span_lint(
self.cx,
MUT_MUT,
ty.span,
"generally you want to avoid `&mut &mut _` if possible",
);
}
}
intravisit::walk_ty(self, ty);
}
fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
intravisit::NestedVisitorMap::None
}
}