blob: 259b4c73d7609b1cef0fe22899f677d41575c195 [file] [log] [blame]
use crate::utils::{higher, span_lint};
use rustc_hir as hir;
use rustc_hir::intravisit;
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::hir::map::Map;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_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 mut y = 1;
/// let x = &mut &mut y;
/// ```
pub MUT_MUT,
pedantic,
"usage of double-mut refs, e.g., `&mut &mut ...`"
}
declare_lint_pass!(MutMut => [MUT_MUT]);
impl<'tcx> LateLintPass<'tcx> for MutMut {
fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
intravisit::walk_block(&mut MutVisitor { cx }, block);
}
fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>) {
use rustc_hir::intravisit::Visitor;
MutVisitor { cx }.visit_ty(ty);
}
}
pub struct MutVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
}
impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
if in_external_macro(self.cx.sess(), 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::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, ref e) = expr.kind {
if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, _) = e.kind {
span_lint(
self.cx,
MUT_MUT,
expr.span,
"generally you want to avoid `&mut &mut _` if possible",
);
} else if let ty::Ref(_, _, hir::Mutability::Mut) = self.cx.tables().expr_ty(e).kind {
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::TyKind::Rptr(
_,
hir::MutTy {
ty: ref pty,
mutbl: hir::Mutability::Mut,
},
) = ty.kind
{
if let hir::TyKind::Rptr(
_,
hir::MutTy {
mutbl: hir::Mutability::Mut,
..
},
) = pty.kind
{
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(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
intravisit::NestedVisitorMap::None
}
}